Poster Abstracts
Title: Petrographic Analysis of the Giants Range Batholith in Northeastern Minnesota
Authors: Lauren Pardi, Zsuzsanna Allerton, Christian Teyssier
Abstract: The Giants Range Batholith is a large granitoid characterized by the abundance of quartz, plagioclase, alkali feldspar that stretches 40 km in a northeast-southwest direction and covers about 2500 km 2 in northeastern Minnesota (Allison, 1925). The Giants Range Batholith (~2.7Ga) is in contact with the gabbroic Duluth Complex, the intrusive suite of the well-known Midcontinent Rift System (~1.1 Ga) to the east. The emplacement of the intrusion generated temperature and pressure changes and introduced hydrothermal fluids, resulting in contact metamorphism, hydrothermal alteration, deformation, and reaction textures with varying intensity as a function of distance from the Duluth Complex-Giants Range Batholith contact. Samples collected from the contact westward into the Giants Range Batholith unit allowed for a systematic approach to conduct petrographic analysis with transmitted light optical microscopy. Petrographic observation of hydrothermal alterations is characterized by samples displaying change in the presence of contact metamorphic signatures and reaction textures in the form of recrystallized minerals, myrmekite, sericite/chlorite alterations, etc. The different textures in samples across the Giants Range Batholith inform about the reactions that occurred providing insight into hydrothermal and chemical alterations induced by the emplacement of the Duluth Complex and regional metamorphism.
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Title: Zircon geochronology across the Giants Range Batholith in northeastern Minnesota
Author: Marek Poplawski, Zsuzsanna Allerton, and Christian Teyssier
Abstract: The focus of this study is the hydrothermal effect of the Mesoproterozoic (~1.1 Ga) Duluth Complex (DC)—the westernmost intrusive suite of the Midcontinent Rift System (MRS)— on the Archean (~2.7 Ga) granitic-granodiorite Giants Range Batholith (GRB) footwall in northeastern Minnesota. The DC emplacement resulted in contact metamorphism, sulfide mineralization, deformation, etc., but little is known about the hydrothermal effect and its magnitude recorded in accessory minerals.
The accessory mineral zircon is central to the field of geochronology because of its innate ability to resist weathering processes and high temperatures, retain isotopic signatures, and preserve complex textures that can be dated through the U-Th-Pb chronology system to reveal thermal history (Hoskin, 2014). We are interested in Pb loss as a function of hydrothermal alteration. When plotting ratios of 206Pb/238U and 207Pb/235U a discordia line can be formed; in which the lower intercept is the time of hydrothermal alteration, and the upper intercept signifies crystallization age.
Preliminary data of zircon grains from GRB samples show crystallization age of ~2.7 Ga and Pb loss associated with hydrothermal alteration at ~1.1 Ga. In order to strengthen the data and define the magnitude of the hydrothermal output of DC within host rocks, additional samples were collected systematically—from the DC contact with increased distance westward—to better understand the extent of thermal effects in accessory minerals and to interpret thermal history of ancient terrains.
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Title: Simultaneous Measurement of Phase Transitions and Magnetic Susceptibility of Clay Minerals using a High-Temperature Magnetic Susceptibility Bridge
Authors: Kacie Malone, Rashida Doctor, Joshua Feinberg
Abstract: Magnetic and thermal data have long been used to characterize thermodynamic phase transitions in natural samples. Measurements of magnetic susceptibility as a function of temperature are commonly collected using High Temperature Susceptibility Bridges (HTSBs), while thermal analyses are performed separately, utilizing techniques such as Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). These measurements are collected on different instruments, necessitating additional time and larger volumes of material for analyses. Here we demonstrate that it is possible to simultaneously collect magnetic and thermodynamic data using a standard HTSB. Because HTSBs heat samples at a relatively constant rate, deviations in the heating rate provide DTA-analogous information, indicating the occurrence of exothermic and endothermic reactions (Doctor & Feinberg, 2022).
Four clay standards with differing magnetic properties serve as a case study to demonstrate the benefits of simultaneous collection of magnetic and thermodynamic information using a HTSB: nontronite, montmorillonite, gibbsite, and kaolinite. Heating curves were created by interpolating and subtracting each sample run with its associated blank measurement. The heating curves in this study were able to accurately replicate literature values for dehydration reactions in nontronite and montmorillonite, as well as dehydroxylation reactions in gibbsite and kaolinite.
These results integrate magnetic and thermal characterization methods and increase data collection efficiency. This combination of techniques allows users to simultaneously identify ferrous and non-ferrous minerals during a single standard geophysical measurement. The ability to identify both clay and iron oxide/hydroxide minerals in soils is helpful to the study of soil health and carbon sequestration. Similarly, this approach can also help differentiate the provenance of glacial tills and delineate alteration and growth of magnetic minerals during thermally based paleomagnetic experiments. Ongoing efforts focus on the thermal and magnetic characterization of a natural soil sample from the Christina River Basin Critical Zone Observatory in southwestern Pennsylvania.
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Title: Not all compost is rad(ish): how compost and soil quality impact radish growth and taste
Authors: Adora Thao, Vang Moua, Bennett Nguyen Prowell, Nana Vang, Sakura Vue, James
Nins, Christof Zweifel, Amanda Patsis, Lindsey Kimmerling, Luis Santiago-Rosario, Lauren Agnew, David Woods, Emilie Snell-Rood, and Cara Santelli
Abstract: Urban agriculture contributes an estimated 15-20% of the global food supply, and here at Urban Roots we grow around 50 crop varieties and 10,000-15,000 pounds of produce each year. We garden on five urban plots in east Saint Paul, the biggest being Rivoli Bluffs. This site is in the flight path of a regional airport and was previously a dump site. We typically add a load of Ramsey County compost to our garden beds annually to restore depleted nutrients each season. This compost was easily accessible, but we noticed that crops grew slowly and not even weeds would grow on the compost pile. We figured something might be wrong with either our soil, the compost we got from Ramsey County, or both!
We investigated our soils to figure out what was affecting our plant growth. Radishes were grown in 5 different soil treatments, 3 soils from the Rivoli site and 2 composts from Ramsey County and Urban Roots. We recorded radish germination rates and dry weight of plant roots and shoots, as well as the overall taste of the vegetables. We measured soil chemistry using ion chromatography, pH meters, and X-ray fluorescence, and sent samples to the University of Minnesota Soil Lab for further analysis.
Radishes grown in the Urban Roots compost did not taste significantly better or worse than those grown in Rivoli soils. However Ramsey compost grown radishes tasted significantly worse than those grown in hilltop and hillside soil from Rivoli Bluff. Compared to the other treatments, Ramsey compost had higher concentrations of salt and nitrate, which has been shown to worsen the taste of vegetables in other studies.
While compost is generally considered beneficial for soil health and plant growth, our results suggest that compost is not always needed and it’s important to consider the source of the compost. We think that the Ramsey County compost is contaminated with trash from street sweeping and community members incorrectly composting, as we’ve found wrappers, plastic dolls, and other materials that aren’t organic or compostable. Trash, road salt, and high nitrate may contribute to this compost producing the least tasty radishes. As an organization that farms and distributes our produce locally, understanding how our soils affect plant growth and taste helps us produce good food and grow healthy communities.
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Title: Characterizing iron-rich layers in Bahamian speleothems
Authors: R. Doctor, J. Feinberg, P.M. Chutcharavan, R.L. Edwards, D.A. Richards
Abstract: Reconstructing sea-levels in The Bahamas provides a window into the spatial and temporal variability of the Earth’s past responses to climate change. This project aims to characterize the chemical and physical properties of a thick red layer within Bahamian cave records that coincide with major fluctuations in sea level during Marine Isotope Stage 7 (~225ka). The flowstone of interest has a thick (~1mm) red layer that corresponds to a hiatus in speleothem growth. We characterized this layer using optical, magnetic, and electron microscopy techniques. Based on the mineralogy and morphology of these samples, we hypothesize the iron oxides in this layer formed in a two-part process. Bahamian blue holes have significant stratification of their water chemistry and fluctuations in sea level would change the water chemistry around the flowstone. The main iron-rich material found in the red layer is in the form of framboids, a morphology common to pyrite formed in euxinic and dysoxic conditions. Later oxidation then transformed the pyrite into iron-oxide pseudomorphs such as hematite. Ongoing measurements on these samples include using the electron microprobe to look for remnants of sulfur in the framboids and characterize the layer chemistry with higher resolution.
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Title: Visualization of Agriculturally-Induced Pollution across the Otter Tail Watershed and its Broader Implications for Decline of Manoomin/wild rice
Authors: Madeline Dickenscheidt, Amelia Olsen, Cara Santelli
Abstract: The Otter Tail Watershed of west-central Minnesota lies just at the Minnesota/North Dakota border and extends north, where its headwaters are found within the White Earth Band of Minnesota Chippewa Tribe Reservation. The watershed is rich in bodies of shallow lakes and rivers that are critical for Manoomin (Ojibwe) or wild rice (Zizania palustris) growth; indigenous peoples of White Earth Nation hold rights to rice on both the reservation and ceded territory in the Otter Tail watershed. Land use cover data shows that a majority of the watershed is designated as agricultural use, which heightens concern for wild rice and, in turn, ecosystem health if excess nutrient and chemical pollutant runoff from fertilizers and animal waste were to be introduced into surface and groundwater. Successful growth of wild rice is dependent on a number of factors, including an absence of water level fluctuations and clear, high-quality water. In agriculturally-impacted waters, an overabundance of nutrient anions such as nitrogen and phosphorus in both surface and groundwater can result in eutrophication. This causes algal growth that blocks sunlight and eventually, during the decomposition of organic matter, reduces dissolved oxygen in the water to a level unsuitable for wild rice production. Initial examination of data acquired from the Minnesota Pollution Control Agency (MPCA) and the Minnesota Department of Natural Resources (MNDR) suggests that average levels of both nitrate and phosphorus in surface and groundwater are higher than standards set by the Environmental Protection Agency (EPA) and the MPCA; concentrations are also consistently elevated in groundwater, likely attributed to longer residence times. Large standard deviations across datasets present extremities in concentrations above set limits in certain areas of the watershed, suggesting the existence of impaired bodies of water no longer suitable for Manoomin. Referencing water quality data against land cover data in the watershed points to cultivation and development being the two most immediate causes of water quality degradation. Although fluctuations in water chemistry can occur naturally, the elevated levels of nitrate and phosphorus seen here point to anthropogenic sources due to the extreme levels that were observed. Lack of consistency in sampling patterns diminishes the ability to produce a more definitive conclusion on the evolution of anion concentration over the observed time period (1960-present).
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Title: Deposition of forever chemicals (PFAS) on the Greenland Ice Sheet: an ice core study
Authors: Sydney Waldrop and Joel Barker
Abstract: Per- and polyfluoroalkyl substances (PFAS) were first developed in the United States in the 1930s and their use in consumer and industrial products proliferated in the following decades. These compounds resist degradation for hundreds to thousands of years and thus are colloquially referred to as “forever chemicals”. PFAS bioaccumulate in the environment and organisms and have the potential to pose a long-term environmental and human health risk factor. PFAS are globally distributed in air, water, soil, and animal and human bodies. While specific toxicity indicators are still being sought, it is believed that exposure to PFAS increases the likelihood of high cholesterol, liver damage, birth defects, thyroid disease, and cancers. Greenland is geographically far from point sources of pollution, yet Greenlanders report high levels of PFAS in blood and tissue samples. While bioaccumulation through a marine-based diet has been identified as a possible vector, the potential for direct atmospheric deposition into freshwater sources and food products has not been investigated. The transportation of PFAS to the Greenland Ice Sheet can occur with precipitation and marine aerosol deposition, and a record of this deposition may be preserved in glacier ice and snow. In order to quantify the deposition of PFAS on the Greenland Ice Sheet, two sections from the Dye-2 ice core were analyzed. Section 1 (historical) was deposited between 1723 and 1728, prior to the development of PFAS. Section 2 (modern) was deposited between 1974 and 1978, after the advent of PFAS. Sections 1 and 2 were analyzed for concentrations of 24 PFAS substances using electrospray ionization mass spectrometry. The modern ice core section contained higher concentrations and different PFAS compounds than the historical section, indicating that a) PFAS are being deposited directly onto the Greenland Ice Sheet and b) the ice core drilling technique introduced PFAS compounds into the sample. These results suggest that even remote locations are at risk of PFAS exposure and accumulation and that future snow and ice melt may remobilize PFAS in meltwater, posing potential risks to human and ecosystem health. Further, ice core drilling and storage methods may have to be modified if ice core studies of PFAS are undertaken.
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Title: Digitized Map of the Ruby Gap Complex in Central Australia
Authors: Joshua Schultz, Hannah Tebbens, Christian Teyssier
Abstract: The Ruby Gap Duplex in Central Australia is defined by three regimes of quartzite characterized by varying strain rates and temperatures. Due to the unique structural geology of the region and clear metamorphic signatures present within the units, the Ruby Gap Duplex can be used as a natural laboratory for quartzite deformation studies. To further understand these deformation patterns, a georeferenced map of the duplex was produced using GIS software, drawing from W.J. Dunlap's paper map (1997), and quartzite photomicrograph data. Dunlap’s paper map was scanned and digitized on the free program called Inkscape. The digital version was simplified, focusing on major faults and lithologic units and contacts. This map was transferred to QGIS where quartzite samples were georeferenced. 58 samples were analyzed by using photomicrographs generated by transmitted light petrography and categorized based on deformation regimes. Finally, the samples were georeferenced and color-coded on the digitized map. This data set will allow for a better spatial understanding of deformation patterns associated with the Ruby Gap Duplex.
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Title: Dark Fenton Reactive Oxygen Species Generation at the Sediment Water Interface of Prairie Pothole Wetlands
Authors: Maricia Pacheco, Cole Stenberg, William Arnold, Brandy Toner
Abstract: Globally, small shallow wetlands emit significant amounts of carbon dioxide and methane to the atmosphere. While the role of biotic processes are well studied, the contributions of abiotic reactions to C emissions is poorly constrained. Reactive oxygen species (ROS) are unselective reactants that are capable of oxidizing available carbon. We hypothesize that ROS are produced in the absence of light through dark Fenton reactions at the sediment-water interface (SWI) of Prairie Pothole wetlands. At the SWI, sharp redox gradients, oxic overlying water, and dark conditions are present. These conditions are ideal for the formation of ROS through dark Fenton reactions, which occur when reduced iron and oxygen interact. This study used a combination of field and laboratory based experiments to understand dark Fenton ROS generation. Porewater and sediment was collected from the USGS operated Cottonwood Lakes site located northeast of Jamestown, North Dakota. X-ray absorption near edge structure (XANES) spectroscopy was conducted at the Advanced Photon Source and National Synchrotron Light Source II to identify iron speciation of sediment. We hypothesized that iron sulfide minerals would be the major reductants found in this region. However, our XANES results indicate that most of the iron was found as a silicate mineral with a minor contribution from iron sulfide minerals. These minerals were primarily in Fe(II) valence states. Iron speciation results were used to guide our reactor experiments. ROS generation from synthesized mackinawite and natural samples was measured using a fluorogenic probe (terephthalic acid). Preliminary results suggest that ROS is generated under dark conditions when iron sulfide minerals interact with oxygen. The present study provides information on how abiotic processes impact ROS generation in wetlands.
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Title: Sugar Beet Production: Investigating the Effects of Cover Crops on Yield, Quality, and Soil Health
Authors: Mehmet Ozturk, Anna Cates, Lindsay Pease
Abstract: Sugar beet is a significant crop in Minnesota, the leading state in U.S. in sugar beet production. However, sugar beet production can cause excessive soil degradation due to the lack of organic matter on the soil surface and the use of heavy machinery, resulting in increased erosion rates. It is substantial to consider implementing sustainable management practices to mitigate these adverse impacts. Integration of cover crops and reduced tillage can prevent or alleviate the current issues and contribute to soil health in this system. Here, we present the findings from the first year of our experiment. The effects of cover crops on soil health, sugar beet quality, and yield were investigated through on-farm and in-station experiments (two farm and two station experiments). After the harvest of wheat or corn, cover crops were planted as both fall and spring cover crops for all experiments, except for one station experiment, where cover crops were interseeded in the early summer. The strip-till method was applied in all experiments and agronomic strategies of farmers were followed for the on-farm experiments. Contrary to some other research, the cover crops did not have a negative impact on the quality or yield of sugar beets in the experiments. However, the combined effects of volunteer wheats and extended termination due times resulted in decreased yield and quality for all plots in one of the experiments. Positive effects of cover crops on soil health were observed in our experiments. In conclusion, the results from the first year demonstrates the potential of cover crops to promote soil health while showing no adverse effects on sugar beet yield and quality, providing valuable insights for sustainable agricultural practices.
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Title: Microbiome sequencing provides insights into microbially-mediated lead transformations in urban gradient soils
Authors: Madeline Taylor, Cara Santelli, Luis Y. Santiago-Rosario, Amanda Patsis, Emilie Snell-Rood
Abstract: Urban ecosystems accumulate lead (Pb) through wastewater, industrial materials, and runoff. Plants store Pb from the soil in their tissues, making urban green spaces potential hotspots for human Pb exposure. Rhizosphere soil microbes transform Pb species and influence Pb availability for plant uptake through processes like chelation and methylation. Understanding the role of soil microbes in Pb cycling could help decrease illnesses from Pb exposure, however, microbial genes related to Pb transformation have not been characterized. We aim to find genes associated with soil Pb transformation through microbiome and metagenomic sequencing. Here, we extracted microbial DNA from the rhizosphere soil of six plant genera and bulk soil at urban and suburban sites in Minneapolis, MN. We used a handheld X-ray fluorescence spectrometer to measure the soil Pb content and found a significant difference between urban and suburban soils. Using targeted bacterial 16S rRNA gene amplification, we are examining microbial abundance, diversity, and taxa to compare data between urban and suburban sites, and between plant genera. We will use the microbiome data to select representative samples for shotgun metagenome sequencing to help identify genes of interest involved in metal transformation and detoxification. We will analyze the metagenomes of microbes living in the high Pb urban site for genes similar to those in known metal detoxification pathways, such as the gene clusters that encode methyltransferases for As and Hg detoxification, as these may indicate genes essential for Pb transformations.
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Title: Experimental and numerical investigation of dislocation-based transient creep mechanisms in the upper mantle
Authors: Abigail Wilwerding, Shanti Penprase, Andy Wickert
Abstract: Glacial meltwater floods raise river levels downstream, in turn elevating base level for their tributaries, whose lower valleys collect slackwater sediments in lacustrine-like depositional environments. These slackwater deposits—comprising fine sands, silts, and clays transported in floodwaters—record chemical and lithological signatures of their glacial provenance. Here, we decipher the late-stage deglacial history in the upper Mississippi Valley, USA, by analyzing such slackwater sediments. We examine four cores from a terrace 20 m above the Whitewater River, a tributary to the once-proglacial Mississippi River in southeastern Minnesota. The cores contain ~4.88 m of interbedded cm- to mm-thick red, gray, and brown silty clay and sand beds, distinct from the sandy fluvial terrace deposits below. Single-grain Optically Stimulated Luminescence dates indicate the laminated slackwater sediments were deposited at 11.67±1.51 ka (1.16–1.64 m depth) and 11.56±1.44 ka (2.36–2.59 m depth). These dates overlap with the ~11.6–10.6 ka Marquette Advance of the Laurentide Ice Sheet, in which glacial ice reoccupied the Lake Superior basin. This readvance may have driven the dated reoccupations of the southern outlets of both Glacial Lake Agassiz and Glacial Lake Duluth in the modern Lake Superior basin. Deposit colors suggest alternating Agassiz and Superior sources. To test for possible western (Agassiz) and eastern (Superior) meltwater sources, we turn to both classic lithologic descriptions and X-ray Fluorescence (XRF), with the latter providing elemental compositions. Previously studied slackwater deposits from the Superior Lobe were rich in Fe, Cu, Zr, Ti, Mn, Ni, Cr, and Co, whereas Des Moines lobe (Agassiz Basin) deposits were rich in Se, Ca, Ar, Cd, Mo, and Zn. Preliminary analysis of the XRF results confirms that the slackwater deposits are distinct from the locally derived sandy terrace materials in the bottom ∼10cm of the core. Going forward, we will fingerprint these slackwater sediments to source regions throughout the analyzed core. The results from this study will contribute valuable insights into the final meltwater pulses to enter the Mississippi River, including their sources and constraints on paleodischarge, and expand our knowledge of early-Holocene ice-sheet evolution in North America.
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Title: Multidecadal Climate Variability in Large Model Simulations o and Proxy Records of the Past 1000 years
Authors: Alejandro Fernandez, Byron A Steinman, Michael E Mann
Abstract: Internal climate variability is broadly defined as that which is not influenced by external factors to Earth’s climate system, such as volcanic eruptions, orbital configuration, or human impacts. Although the physical mechanisms that cause some modes of internal variability such as ENSO (El Nino – Southern Oscillation) are well understood, observations and climate models suggest that there exist lower-frequency cycles whose underlying causes are still a matter of debate. Such is the case of the Atlantic Multidecadal Variability (AMV), a sea-surface-temperature pattern of variability in the North Atlantic that has been hypothesized as being linked to long-term changes in the Gulf stream and heat transport from the tropical Atlantic. Although evidence exists for semi-oscillatory behavior in the multidecadal frequency band in historic (1850CE – present) simulations and observations, some authors have related this evidence to anthropogenic greenhouse gas emissions and sulfate aerosols. Here, we explore the extent to which Last Millennium simulations (850 – 1850CE) showcase evidence of AMV variability by conducting multivariable, spatiotemporal spectral analysis on the Last Millennium Ensemble (LME) of simulations of the CESM model, as well as other models belonging to the Climate Model Intercomparison Project (CMIP6). In the case of the LME, we take advantage of the ensemble size to estimate the forced signal of variability by computing the ensemble mean, and then estimating each simulation’s internal variability evolution as the temperature field residual. We find that the CESM model shows muted temperature variability in multidecadal timescales, as other models have some evidence of an AMV-like response which may be forced in nature. To complement the model analyses we provide a preliminary compilation and spectral analysis of paleoclimate proxy datasets which span similar timeframes. Our results suggest the absence of a truly oscillatory, internal mode of variability in the multidecadal band as expressed in past millennium simulations, supporting the hypothesis that the observed AMV-like oscillations in models and observations correspond to externally forced variability.
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Title: Discovering the Position of Earth’s Last Geomagnetic Reversal in Sediments from Blackwater Draw, Texas
Authors: Ruby Sandell, Jonathon Stine, Joshua Feinberg
Abstract: The Blackwater Draw Formation (BDF) in Bushland, Texas, composed of alternating layers of loess and soil, is situated in a region known as the Southern High Plains. This region of the southern Midwest lacks significant paleoclimate information due to poor age constraints on the sediments in the BDF. A geochronologic method, referred to as paleomagnetism, is used to better constrain the ages of these sediments by determining the precise locations of ancient magnetic reversals within the stratigraphy. The samples are collected from ~12 m soil core and placed into 7cc non-magnetic plastic cubes, serving as the primary specimens for analysis. The characteristic remanent magnetization (ChRM) is measured using a 2G Cryogenic Superconducting Rock Magnetometer (SRM) that subjects the specimens to step-wise alternating field-demagnetization from 1-100 mT. Preliminary results show consistent zones of normal and reverse polarity that align with known quaternary geomagnetic reversals. The specimens maintained relatively stable magnetic fields under low coercivity conditions (0-10 mT). Locating the position of ancient magnetic reversals within the sediments, thus constraining the age, will relate changes in the sediment record to climate cycles associated with the Early-Middle Pleistocene Transition in North America.
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Title: The role of point defects in the crystal plasticity of olivine
Authors: Hagmar Tinoco Madeira, Lars N. Hansen, Amanda M. Dillman
Abstract: It is well known that the plastic deformation of Earth's lithosphere is largely controlled by the motion of crystal dislocations in olivine. However, the role of the chemical environment in moderating dislocation velocities is still a remaining source of uncertainty. In particular, the chemical environment, such as the oxygen fugacity, influences the concentrations of point defects that may influence dislocation velocity. Overall, dislocation velocities are set by either the rate of dislocation glide or of dislocation climb. It has already been established that dislocation creep in olivine is highly dependent on oxygen fugacity at high temperatures, for which the climb controls the velocity. However, the role of oxygen fugacity has not been investigated at low temperatures, for which glide controls the velocity. Therefore, it is currently unclear if changes in point defect concentrations influence dislocation glide velocities. To address this gap in knowledge, 5 samples consisting of natural single-crystal San Carlos olivine were annealed in a 1-atm gas mixing furnace set to different CO/CO2 ratios (ranging from 50:1 to 1:100) and oxygen fugacities (ranging from 10-11 to 10-2 atm). After annealing, the elastic modulus and hardness of the samples were measured at room temperature, which suppresses dislocation climb, using instrumented nanoindentation with a Berkovich tip. Based on these measurements, the elastic modulus and hardness do not change significantly as a function of oxygen fugacity during annealing, remaining at ~215 GPa and ~13 GPa, respectively. This result demonstrates that, unlike dislocation climb at high temperatures, dislocation glide does not have a dependence on oxygen fugacity and the associated point-defect concentration.
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Title: Dendroclimatology of Northern Minnesota using Thuja occidentalis
Authors: Naomi Schulberg, Daniel Griffin, Kurt Kipfmueller, Andrew Wickert
Abstract: Climate change will likely result in warmer temperatures, higher frequencies of drought, and higher flood risks in northern Minnesota, but sparse long-term climate records exist in the region, limiting our ability to contextualize recent climatic changes. We applied dendrochronological techniques to Thuja occidentalis (northern white cedar), to establish annual to sub-annual long-term records of climate and thus better understand the current context of climate change in northern Minnesota. T. occidentalis presents a promising opportunity to study past climate in northern Minnesota, often living to be over 500 years old, with subfossil wood found to be even older. A pilot study by Kipfmueller showed that T. occidentalis cores from the same stand show synchronized signals which are likely related to environmental factors and can thus be used for climate reconstructions. We created chronologies of earlywood, latewood, and total ring widths from six sites in northern Minnesota, and analyzed their relationship to temperature, precipitation, and drought. Preliminary results show a range of climate responses between sites. The strongest responses identified are a positive relationship with May and June precipitation, and a positive relationship with the Palmer Drought Severity Index from March to August. Additionally, stronger responses to climate were seen at sites in the Boundary Waters Canoe Area Wilderness, as compared to the Cloquet Forestry Center. Future work will involve expanding the current network of chronologies and testing new tree-ring proxy techniques, aiming to identify a stronger climate signal, which can then be used for climate reconstructions.
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Title: Molecular Mechanisms of Algal Growth Enhancement by Phycosphere Bacteria Under Iron Limiting Conditions
Authors: NR Coffey, B Newell, K Manning, RK Stuart, X Mayali, Y Corilo, W Kew, C Dewey, RM Boiteau
Abstract: Iron (Fe) is a critical micronutrient in marine ecosystems, but is difficult to acquire due to its poor solubility. To gain a competitive advantage, some marine microorganisms have developed molecular strategies to bind and uptake Fe from their surroundings. However, most marine algae lack the ability to synthesize these Fe-binding molecules, termed siderophores, and it remains unknown how they access Fe from poorly soluble phases such as dust that represent the major Fe source to the open ocean. Phaeodactylum tricornutum (P. tricornutum) has been a popular diatom to use in nutrient limitation studies as a model organism, as its entire genome is known and its growth is well-characterized. However, most of these studies have been conducted in monoculture, even though P. tricornutum has co-evolved with bacterial partners in environments where low Fe solubility is a dominant ecological control. In this study, we examine how the presence of bacterial partners isolated from P. tricornutum’s phycosphere impact the diatom’s growth under Fe-limited conditions. In experiments using Arizona Test Dust (AZTD, 2-5% Fe2O3 by weight) as the sole Fe source, the presence of one bacterial partner Marinobacter 3-2 significantly improved algal growth under Fe-limited conditions, reaching a final cell density over three times higher than that of the axenic algae. In contrast, Stappia sp. ARW1T significantly inhibited P. tricornutum’s growth, halving the algae’s final cell density after 26 days of growth. Both strains are suspected to produce siderophores, but the identity of those molecules and their potential for use by P. tricornutum remains unknown. Using LC-ESI-MS coupled with novel computational pipelines, we probed the metabolome of axenic P. tricornutum cultures as well as the metabolome of the diatom-bacteria co-cultures to understand the mechanisms behind the observed growth effects. By examining differentially expressed features between high (1 µM) and low (10 nM) Fe conditions in the presence and absence of bacterial partners, we can begin to untangle the molecular basis for algal-bacterial interactions and uncover how bacteria can influence algal growth and resilience.
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Title: Reaction-induced and Background tectonic stresses guide fracture, fluid flow, and serpentinization in the mantle wedge corner
Authors: Jeremiah J McElwee, Ikuko Wada, Kazuki Yoshida, Hiroyuki Shimizu, Atsushi Okamoto
Abstract: During subduction, fluids released by the downgoing slab may react with material in the forearc mantle wedge to form serpentinites. Serpentinization is accompanied by a large volume increase that can stress the surrounding rock and generate fractures, which may act as pathways for more fluids to migrate into the mantle wedge corner, facilitating further serpentinization. However, these reaction-induced fractures are likely dependent on the background tectonic stress state in the mantle wedge corner. We investigate the effect of reaction-induced stresses and background tectonic stresses on fracturing, fluid flow, and serpentinization in the mantle wedge corner of subduction zones using a 2-D brittle-elastic hydraulic-chemical-mechanical discrete element model, and make comparisons to geophysical observations of serpentinization and fluid distributions in subduction zone forearcs.
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Title: Fate and transport of lead within Twin Cities stormwater catchment ponds using inductively coupled mass spectrometry and synchrotron based X-ray absorption spectroscopy
Authors: Christof Zweifel, Ben Janke, Lea Pollack, Timothy Mitchell, Kaya Koraleski, Jacques Finlay, Emilie Snell-Rood, and Cara Santelli
Abstract: Industrial emissions, legacies of leaded gasoline, and the breakdown of lead paint have created a risk for lead contamination in urban environments. In the Twin Cities Metro Area there are multiple sources of lead emissions from the downtown garbage burner, regional airports, smelters, lead paint, and decades long accumulation from leaded gasoline. Sediments, runoff, and the direct input from industrial sources means stormwater catchment areas have the potential to capture lead and other metals within a unique chemical environment. The chemical transformations that lead undergoes from terrestrial, airborne, and dissolved sources into the sediment captured by stormwater ponds determines the concentration and chemical speciation of lead, ultimately impacting lead bioavailability. Bioavailability determines the impact on pond ecology and potential for remobilization of lead from pond sediments. Concentrations of lead and other heavy metals were determined using mass spectrometry (ICP-MS) for the surface water, bottom water, porewater, and sediment of three well studied ponds within the Minneapolis-St Paul Long Term Ecological Research program (LTER). Lead speciation of Twin Cities soils and pond sediments will be determined in late March 2024 using synchrotron based X-ray absorption spectroscopy (XAS). X-ray fluorescence (XRF) data shows lead concentration in urban soils ranging from 20 to 2,000 (ppm), with the EPA’s action level set to 200 ppm. Sediments at the bottom of the three stormwater ponds had a range from 23 to 300 ppm lead. Sediment lead concentrations in two out of the three ponds exceeded 200 ppm, with lead levels generally higher at greater sediment depths in these two ponds.ICP-MS data shows metals such as chromium, nickel, and copper are concentrated by a factor of 10 within stormwater sediment pore waters as opposed to surface and bottom waters. Porewater lead concentrations are between 0 and 0.002 parts per million (ppm) in the dissolved <0.15 micron phase, which is not significantly different from surface or bottom waters. Metal concentrations and speciation offer insight into the types of sources, processes that affect lead fate and transport, and potential remobilization of metals in urban ponds.
Oral Abstracts
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Title: Investigating Lead Sequestration in the Soil Bacterium Bacillus megaterium
Author: Jamison Ward, Beverly Flood, Cara Santelli, Jake Bailey
Abstract: Lead is a priority pollutant whose environmental occurrence has increased since human industrialization with deleterious consequences for both human and natural ecosystem health. The application of lead-resistant microorganisms for bioremediation has received considerable attention for its advantages over physiochemical remediation strategies. The soil bacterium, Bacillus megaterium, has been previously observed to harbor lead resistance and accumulate lead intracellularly; however, the mechanism for lead storage was not entirely elucidated. One possibility is lead sequestration in microbial polyphosphate (polyP) granules—nanometer-scale inclusions of phosphate polymers used as phosphorus storage and cellular energy reserve. PolyP contains metal atoms as counterions, and lead has been observed to associate with polyP in bacteria grown in lead-rich environments. This project employed a suite of analytical methods to investigate the mechanism of lead resistance in B. megaterium with lead storage in polyP as the working hypothesis. The bacterium was cultured to stationary phase in a lead-amended minimal growth medium and examined using epifluorescence microscopy; cells stained with DAPI and tetracycline were observed to harbor abundant polyP granules. Current efforts include imaging selected specimens via STEM-EDS to further investigate cellular morphology and elemental distribution within polyP granules, thereby elucidating mechanisms of intracellular lead sequestration. Additionally, supernatant samples have been prepared for ICP-MS analysis to evaluate lead concentrations throughout the growth experiment. If soluble lead drawdown is observed, the mechanism of lead accumulation in bacterial polyP granules could prove an effective method to remove lead from contaminated soils or wastewater as B. megaterium is native to soil environments and could be integrated into current wastewater treatment processes. Therefore, novel lead bioremediation techniques derived from this research could be employed to maintain safe drinking water and public greenspaces for Minnesota communities, protecting future generations from the deleterious effects of lead poisoning.
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Title: Evaluating the Redox Evolution of Martian Magmas
Authors: Sanath Aithala, Marc Hirschmann, Maria Buss, Jasper Goldstein
Abstract: The influence of oxygen fugacity (fO2) on igneous processes including crystallization, partial melting, degassing, ascent, and assimilation has long been a subject of interest in planetary geology as its consequences include planetary habitability and petrologic diversity. We seek to better understand the martian interior and its magmatic history by characterizing the processes that produced the rocks in the martian rock record. Variations in terrestrial basalt fO2 are attributed to the influence of plate tectonics recycling surface-materials to the mantle, but martian basalt fO2 variation is even greater despite Mars not having plate tectonics. In addition, some martian magmas undergo extents of oxidation (fO2 increase) throughout crystallization much greater than what is observed in terrestrial magmas. Many workers explain the oxidation histories of martian magmas by invoking shallow oxidative processes such as degassing and crustal assimilation, but do not provide quantitative constraints on their feasibility. We present experimental data that quantitatively constrain the relationship between the oxidation state of multivalent cations - primarily iron - in magmas, to fO2 and we use this relationship to model different scenarios of shallow processes that can explain the oxidative redox history of martian magmas.
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Title: Cranial ontogeny in the Early Cretaceous ceratopsian dinosaur Psittacosaurus lujiatunensis: intraspecific variation by age and taxonomic implications
Authors: Minyoung Son, Peter J. Makovicky, Gregory M. Erickson, Chang-Fu Zhou, and Ya-Lei Yin
Abstract: Before using ontogenetically variable character data and character scorings from immature individuals in maturity assessment and taxonomy of fossils, character state changes across ontogeny should first be evaluated at the species level. Psittacosaurus is one of the best-sampled dinosaur genera in the fossil record and the most speciose genus of dinosaur, with ten species currently accepted as valid. Histological data for Psittacosaurus specimens from China, Mongolia, and Russia have been reported, showing different life history strategies for each analyzed species. However, no study has yet comprehensively examined changes in character states or evaluated characters specific to an ontogenetic stage. Here we examined the post-hatchling variation of Psittacosaurus lujiatunensis based on 30 specimens from the Lujiatun Unit (Barremian, Early Cretaceous) of the lowermost Yixian Formation in Liaoning Province, northeast China. Taphonomic effects were accounted for when identifying and scoring variation. Taphonomic processes inferred from articulated skeletons support the presence of only a single species of Psittacosaurus in the Lujiatun bed, with other proposed Lujiatun species exhibiting different skull morphology due to diagenetic deformation. Based on histological ages, specimens range from less than a year old to fully mature individuals more than ten years old. As previously reported, commonly used body measurements are strongly correlated with age. The efficacy of size-independent character changes for assessing maturity and assigning a specimen to an ontogenetic stage was tested by treating the ontogenetic hierarchy as a form of phylogenetic hierarchy (cladistic ontogeny). We built a character matrix of ontogenetically variable characters of the skull defined as binary or multistate transformation series. The matrix was analyzed with TNT, recovering a strict consensus tree (i.e., ontogram). The consensus ontogram is poorly resolved indicating prevalent intraspecific variation, and is incongruent with the ontogenetic sequence of specimens based on age and size rankings. Although some histologically supported age groups cluster in the ontogram, others are separated by varying patristic distances. Some trait combinations proposed as diagnostic of different Psittacosaurus species are in fact observed across the growth series of P. lujiatunensis, meriting a revision of Psittacosaurus diversity and evolutionary patterns.
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Title: A comprehensive database of dissolved riverine rare earth elements (REEs): Seeking the controlling factors from the global perspective
Authors: Weiming Ding, Yves Plancherel, Andrew Wickert, Kate Davies, Chandranath Basak, Xin-Yuan Zheng
Abstract: Dissolved rare earth elements (REEs) in rivers carry useful information on continental weathering, aqueous geochemical processes, and anthropogenic contamination. They also contribute significantly to cycles of REEs and their isotopes in the global ocean. Aquatic geochemistry (such as pH and river-water chemical compositions) has been proposed to influence dissolved riverine REEs patterns and concentrations. Nonetheless, the influence of lithology on the dissolved riverine REEs pool has been overlooked since early times, even though riverine REEs stem from dissolution of parental rocks. In addition, a recent study speculated that truly dissolved riverine REEs patterns resemble seawater REEs patterns based on local observations, highlighting the potential origin of oceanic REEs evolution from the riverine REEs end-member. However, the relationship between riverine and seawater REEs characteristics remain unexplored on a global scale. A compilation of riverine REE data and detailed analysis of the controls on REE concentrations and patterns in global rivers is, therefore, valuable.
To better understand the behavior and distribution of riverine REEs, we compiled dissolved riverine REEs concentration data. This new compilation includes 1981 dissolved and 114 truly dissolved REEs datapoints sampled from ~160 rivers and their tributaries in 28 countries. Using this compilation, we provided discharge-weighted annual gross riverine REEs fluxes, and updated net riverine REEs fluxes to the ocean by compiling the riverine REEs removal percentages during estuarine mixing processes, providing more robust constraints on the REEs input to the ocean. In addition, direct comparisons between truly dissolved riverine REEs and seawater REEs pools were conducted. Seawater-like REEs patterns can be observed in finer-filtered truly dissolved riverine REEs fractions. Nonetheless, further chemical fractionations of truly dissolved riverine REEs are still needed to decrease the REEs concentrations and Ce anomalies. Furthermore, Geographic Information System analyses was applied to extract lithological information in the watershed for each REEs sampling point based on their coordinates according to global lithological database. Our data confirm the significant influence of watershed lithologies on the riverine pH, REEs concentrations, patterns and Eu anomalies, which underscores the importance of REEs characteristics in the geological terrains on shaping the riverine REEs.
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Title: Unraveling viscous remanent magnetization of cave formations
Authors: Emma Kostecki, Plinio Jaqueto, & Josh Feinberg
Abstract: The efficacy of using viscous remanent magnetization (VRM) as a tool for dating geological materials has been debated since no general method has been established. Successful applications involve Hadrian’s Wall, Icelandic glacial floods, and movements of boulders due to tsunamis. The technique relies on the presence of the fine scale grain sizes of magnetic minerals that are able to acquire new magnetization when a new orientation is established. One of the materials that has not been explored are speleothems. Speleothems are secondary carbonate formations in caves, such as stalagmites and stalactites, and are natural recorders of the Earth’s dynamic past. During formation, trace concentrations of magnetic minerals are incorporated into their matrix and record the Earth’s magnetic field at the time of formation. Results from all over the globe show the ubiquitous presence of a secondary magnetic component. Although they have not been studied, these secondary magnetizations offer the possibility to be used as a dating tool for past tectonic events, past human occupation in caves, and paleofloods.
In this study, we explored the magnetic mineralogy and the acquisition of viscous remanent magnetization of a stalagmite sample. Our goal was to establish a robust analytical time-dependent expression for the acquisition of VRM. We applied two protocols to unravel the viscous component. We demagnetized at small temperature steps to define the temperature range where the viscous component is defined, and calculated the grain size distribution that is required for this acquisition. Next, we simulated the acquisition of VRM in a controlled laboratory environment, by changing the initial states of the specimens. We were able to define the time required to gain a new vector magnetization. By fitting a curve to this acquisition, the mathematical model can be used to date orientation changes in the sample.
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Title: Historical snow-drought-streamflow relationships in a sensitive aquatic ecosystem: Understanding the consequences of snow drought for wild rice
Authors: Paige R. Voss, G. H. Crystal Ng, Daniel J. Larkin, William (Joe) Graveen, Shaoqing Liu
Abstract: Wild rice, or Manoomin/Psiη (Ojibwe/Dakota), is an aquatic grass native to the Upper Midwest that grows annually in slow moving lakes and rivers. Wild rice holds great cultural and spiritual significance as a sacred relative for Ojibwe, Dakota, and other Indigenous peoples. However, wild rice has declined significantly in response to the environmental stressors triggered by Euro-American settler-colonialism, including changes in water levels and flow rates. As part of a university-tribal collaboration, our work focuses on a culturally significant wild rice river on the Lac du Flambeau Band of Lake Superior Chippewa Indians Reservation in Northern Wisconsin, which has experienced a decline in wild rice in some reaches. Ongoing research shows that wild rice abundance is positively correlated with greater snow accumulation, among other factors. We hypothesize that the hydrologic perturbations caused by low snowfall exacerbate the preexisting stressors affecting wild rice. Since snowmelt magnitude and timing plays a large role in discharge dynamics in this region, differences in snow accumulation have potential consequences for wild rice during its crucial germination, submerged, and floating-leaf life stages. Comparing the historic spring discharge of years characterized by high snowfall to those experiencing snow droughts, we see consistently lower discharge rates during the germination and submerged stage following snow drought winters, even when the winter precipitation was comparable to that of high snow years. Furthermore, discharge levels remain higher late into the summer following winters with high snow accumulation. This potential link between snowfall, water levels, and wild rice raises concern because current climate projections show considerable decreases in snowfall, snow depth, and snow season length for the Upper Midwest by 2100.
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Title: Terrestrial, deep, subsurface microorganisms fuel metabolism with linked organic and inorganic sulfur cycles
Authors: Amanda Patsis, Cara Santelli, Cody Sheik
Abstract: Organosulfur compounds (OrgS) have been increasingly recognized as a central aspect of biogeochemical S cycling in marine and freshwater surface systems, providing substrates for growth and a source of inorganic sulfur to drive chemoautotrophy. The importance of OrgS compounds in the terrestrial deep subsurface, however, remains unexplored. Here, we employ shotgun metagenomic sequencing of deep biosphere communities from Soudan Mine to probe the genetic potential for OrgS cycling and to elucidate the role these compounds play in supporting deep terrestrial life. Our findings demonstrate that a taxonomically diverse microbial community has the capacity to support an active OrgS cycle, with dimethyl sulfide and taurine playing a central role. Organic and inorganic sulfur cycling processes are inextricably linked in this system, with the assimilation and mineralization of OrgS compounds impacting the availability of inorganic S substrates. Specifically, OrgS degradation provides a key connection between the organic and inorganic S cycle through the generation of sulfite or sulfide, which can then be used in redox reactions to generate ATP. Our results are further contextualized through a comparison to other deep biosphere communities sequenced through the Census of Deep Life, which supports the importance of a linked organic and inorganic S cycle and highlights the role of OrgS as a source and sink of inorganic S compounds across the terrestrial deep subsurface. Continued exploration into the scope and scale of microbially driven OrgS cycling will refine our understanding of deep subsurface biogeochemical sulfur cycling and how it impacts larger Earth systems.
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Title: Soil Carbon and Nitrogen Stocks Across Hillslopes Underlain by Continuous Permafrost in the Northern Arctic Foothills, Alaska, USA
Authors: I.A. Ainuddin, N.A Jelinski, R. Matamala, C.L. Ping, J.D. Jastrow
Abstract: Constraining the variability of soil organic carbon (SOC) and total nitrogen (TN) stocks across hillslopes in permafrost-mantled terrain of the low Arctic remains a significant challenge for improving uncertainties in global estimates of permafrost SOC stocks. Despite studies focusing on SOC and TN stocks across regional climate gradients in the northern circumpolar region, the lack of quantitative SOC and TN stock data across hillslope toposequences introduces large uncertainties in SOC estimates at regional and global scales. We investigated SOC and TN stocks across hillslopes at two locations in the Arctic Foothills of Alaska, USA (Happy Valley and Sagwon Hills). Average SOC and TN stocks for the 0-1 m depth interval were high (51.5 7.6 kg C m-2 and 2.75 0.34 kg N m-2) and linearly related (R2 = 0.74, p < 0.0001) but unlike soils of other permafrost and non-permafrost landscapes, variability was greatest within rather than between hillslope positions. Furthermore, SOC and TN stocks in the top 1m did not exhibit strong patterns by hillslope position nor were they closely associated with major geomorphic parameters (i.e. slope and curvature) that are typically predictors of SOC and TN stocks across most landscapes. The unique small-scale variability in ground ice content, cryoturbation, patterned ground, and organic layer thickness on these broad, Low Arctic sites contributes to the relatively homogeneous distribution of SOC and TN stocks across hillslope positions. This work underscores the need for and importance of local toposequence studies to underpin broader regional-scale predictive efforts.
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Title: Solutes as tracers of streamflow components in an agricultural headwater catchment in Southern Brazil
Authors: Alice Dambroz, Paul Capel, Jean Minella, Fábio Mallmann, João Henrique Silva, Felipe Bernardi, Larissa Werle, Fabio Schneider and Gustavo Merten
Abstract: Streamflow depends on precipitation and the hydrological characteristics of the watershed. Surface runoff (fast flow) is one component of streamflow which happens during rainfall events, temporarily increasing discharge. Another component is baseflow (slow flow), which slowly discharges water to a stream in-between events. Understanding the components of streamflow is important for water resources management, especially for maintaining adequate discharge over the year to avoid impairments to the environment. Solute concentrations during events may be used as end-members to infer on the sources of fast and slow flows. No-till agriculture, topographic gradients, a geological transition, and different soil classes characterize Guarda Mor catchment in southern Brazil. Rainfall and streamflow are monitored in this catchment, at a high temporal resolution. Manual water samples are collected during events to quantify calcium (Ca) and magnesium (Mg) concentrations. Eight rainfall events that occurred between April 2022 and September 2023 were analyzed. The baseflow index (BFI) was calculated for each event by using the dissolved concentrations in an end-member mixing analysis (EMMA) and by a hydrograph separation modeling tool. For the EMMA analysis, the maximum Ca and Mg concentrations in each event were considered as the slow flow end-members, while for fast flow, concentrations in rainfall were used. Eckhardt’s digital filter was used for hydrograph separation of individual events, and median BFI were between 0.84 and 0.99. Median BFI in Ca-EMMA ranged from 0.66 to 0.98, and between 0.60 and 0.92 for Mg-EMMA. Eckhardt and Mg-EMMA’s BFI have positive correlations to 24 and 48h antecedent precipitation, and negative correlations to 120 and 168 h antecedent precipitation, discharge, and rainfall’s kinetic energy. Differently, Ca-EMMA’s BFI has a positive correlation to 24 and 48 h antecedent precipitation, discharge, and rainfall’s kinetic energy. Comparing the shifts in fast flow can provide information on stream recharge over the year and aid the planning of management practices that improve water infiltration.
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Title: Seasonal variation of CO and CO2 concentrations and fluxes above an urban footprint in Greater New York
Authors: Trey A. Maddaleno, Dylan B. Millet, Michael P. Vermeuel, Katelyn L. Rediger, Jeff Peischl, Emily B. Franklin, Delphine K. Farmer
Abstract: Carbon monoxide (CO) and carbon dioxide (CO2) play key roles in the urban atmosphere as pollutants, combustion products, and endpoints of volatile organic compound (VOC) oxidation. In complex urban environments, the two species can also be used as tracers to quantify the importance of VOC emissions from combustion & traffic relative to non-combustion sources including volatile chemical products. However, this potential is underexploited as few studies have combined direct flux measurements of CO, CO2, and VOCs in urban environments. During both a summer and wintertime sampling period, the ‘Fluxes of Reactive Organic Gases in New York’ (FROG-NY) project used the eddy covariance method from two heights (32.5 and 60 m) on a cellular tower in Long Island, NY to directly quantify trace gas fluxes over an urban environment. Fast, simultaneous measurements of CO2, CO, and N2O were collected alongside comprehensive VOC measurements from H3O+ and I- chemical ionization time-of-flight mass spectrometers. Here, we present a first look at the observed CO and CO2 fluxes and concentrations along with their connection to traffic sources.
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Title: Experimental and numerical investigation of dislocation-based transient creep mechanisms in the upper mantle
Authors: Diede Hein, Lars N Hansen
Abstract: Transient creep of olivine in the upper mantle plays an important role in large-scale Earth processes such as glacial isostatic adjustment and postseismic creep, as well as (exo-)planetary tidal heating and orbital dynamics. Yet, an experimentally confirmed microphysical understanding of transient creep across all timescales relevant to Earth processes remains elusive.
The time-dependent dissipation of strain energy during transient creep manifests as attenuation, Q-1, in the frequency domain. Therefore, constitutive equations of proposed transient creep mechanisms should be able to predict the attenuation in polycrystalline olivine subjected to forced oscillations. Here we present numerical investigation of the nonlinear constitutive equations of two contending mechanisms in the frequency domain and comparisons thereof to the mechanical results of a set of high-stress, forced-oscillation experiments on polycrystalline olivine performed in a deformation-DIA coupled with synchrotron analysis techniques. Key microstructural variables needed to inform these comparisons, such as grain size, viscous anisotropy, and dislocation density, were obtained from electron backscatter diffraction and dislocation decoration.
Numerical analysis of the constitutive equations yields high Q-1 values, up to ~5, which is similar to the experimental observations. We find that the experimental observations are consistent with predictions from the backstress model for the grain sizes and dislocation densities of our samples. When extrapolated to lower stress amplitudes, the backstress mechanism produces approximately linear behavior and behaves as a Burgers model in frequency space, suggesting that dislocation interactions may contribute to seismic wave attenuation as well.
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Title: Conserving Soil During Perennial Crop Termination
Authors: Jake Kundert; Manbir Rakkar; Jessica Gutknecht; Jacob Jungers
Abstract: Mechanical termination of crops can negatively affect soil biological, chemical, and structural characteristics. Perennial crops do not require annual termination and can improve these same soil characteristics, which has catalyzed interest in the development of new perennial crops. Advanced lines of the perennial grass intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth and Dewey; IWG) have been bred for increased seed size and marketed as Kernza® perennial grain, but little is known about how this new crop can be terminated for subsequent annual crop production in rotations that enhance agricultural productivity and environmental sustainability. Five methods of terminating IWG were tested in Rosemount, Minnesota. Treatments included mechanical tillage using a chisel plow (CHI), undercutter (UND), and disc (DSC), along with no-till treatments of glyphosate (GLY) and a repeated-mowing control (CTRL). Treatment effects on IWG mortality, soil carbon dioxide (CO2) emissions, bulk density, aggregate stability, soil carbon stocks and soybean yield were measured. Daily CO2 fluxes differed by treatment (p < 0.05) on only one of 19 sample dates, and cumulative soil CO2 emissions over the course of the growing season did not differ across treatments. Bulk density decreased relative to baseline in all treatments except CTRL. Aggregate stability remained unchanged in all treatments except CTRL, which increased from the baseline. Soil carbon stocks did not change in any treatment. Soybean yield was highest in GLY but was not significantly different from CHI or UND. Soil structure, soil carbon stocks and soil CO2 emissions were unaffected by tillage and no-till IWG termination treatments. However, tillage followed by pre-planting harrowing proved ineffective at terminating IWG and required subsequent summer herbicide applications. Therefore, additional tillage events may be required to fully terminate IWG when herbicide use is prohibited.
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Title: Fluvial Mobility of Hadrosauroid Dinosaur Skeletons: Experimentally Testing Transport Potential in Extinct Reptiles
Authors: Michael Chiappone, Michele Guala, Raymond Rogers, Peter Makovicky
Abstract: The fossil record is our primary window into understanding extinct ecosystems, and understanding the taphonomic processes that shape it is integral to interpreting the record of extinct life. Bones preserved in fluvial environments make up a major part of the terrestrial vertebrate fossil record, and unsteady state flows (flooding, crevasse splays, debris flows) are often invoked as drivers of mobility and burial of skeletal elements. Actualistic experiments have explored the fluvial taphonomy of mammal skeletons, but other terrestrial vertebrates, especially extinct clades, have only been sparingly studied. Because of this, researchers have raised concerns that the morphologies of non-mammalian bones would result in different hydrodynamic properties and mobility patterns. Being known from extensive remains across the globe, hadrosauroid dinosaurs make an ideal group for this kind of taphonomic study. Here we investigate the mobility of postcranial bone models of the hadrosauroid, Eolambia caroljonesa, and skull elements of Edmontosaurus regalis, using 3d printed bones weighted to feasible densities in a large-scale flume setup. We find that in unsteady state flow conditions at two discharge levels, our bone models sort into statistically significant transport groups based on movement distance. These groups are broadly similar to Voorhies Groups, although the modes of mobility and groups certain elements sort into is variable due to differing morphologies from the sheep skeletal elements we tested under the same conditions. While distance-based groups were evident among hadrosauroid bones, such groupings were less clear among the more continuously distributed sheep bones. Voorhies Groups were originally constructed from qualitative observations on the order and mode of bone movement rather than transport distance or competent velocity. In the quantitative context of our study, it was not possible to match the sheep skeleton to the originally established Voorhies Groups in a statistically significant and non-arbitrary manner due to their somewhat continuous distribution of transport distances. We also find that both shape and mass were significantly correlated with transport distance by both hadrosaur postcrania and sheep bones, which is suggestive that travel distance in absence of other obstacles relies on both of these characteristics.
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Title: Isotopic evidence reveals limited mobility in the short-legged rhinoceros Teleoceras major at Ashfall Fossil Beds, USA
Authors: Clark T. Ward, Brooke E. Crowley, Ross Secord
Abstract: We use carbon (C), oxygen (O) and strontium (Sr) isotopes to evaluate multiple types of mobility in Teleoceras major from Ashfall Fossil Beds, Nebraska. Ashfall is a mid-Miocene (ca. 12 Ma) site that preserves hundreds of T. major skeletons in a volcanic ash-filled watering hole. This Laggerstätte provides a temporal “snapshot” of T. major population dynamics and allows us to test three possible types of mobility: (1) sex-specific (male) ontogenetic dispersal; (2) seasonal migration; and (3) retreat to a refugium in response to the catastrophic volcanic event. To test for dispersal, we bulk sampled lower m2’s and m¬3’s from five males and eight females; m2’s formed after weaning but before cow-calf separation, while m3’s formed between cow-calf separation and sexual maturity. To test for seasonal migration, we serially sampled m2’s and m3’s from two males and two females. Lastly, we compared isotope data for T. major with other ungulates from Ashfall to detect possible perimortem mobility and niche partitioning. We found only one significant isotopic shift between bulk-sampled m2’s and m3’s for either sex: C isotopes for female m2’s were ca. 0.5‰ higher than female m3’s. This is too small of a difference to worry about confidently assign a single driver. There were also no significant isotopic differences between sexes for either m2’s or m3’s. Oxygen isotopes oscillated by ca. 2‰ for all serially sampled teeth, which likely reflects seasonal climate fluctuations. In contrast, the range in C isotopes was <1‰, and the range in Sr isotopes was within analytical uncertainty (±0.00003). Finally, O and Sr isotopes distinguish T. major from co-occurring ungulates, especially horses. Combined, these results suggest that the sampled T. major individuals were local to Ashfall throughout their lives. They did not arrive from elsewhere (due to ontogenetic dispersal or catastrophe), nor did they seasonally migrate. To avoid inbreeding and intraspecific competition, individuals may have socially (rather than spatially) dispersed among co-occurring groups. Small but significant isotopic differences among ungulates indicate niche partitioning; Teleoceras major at Ashfall likely inhabited wet habitats. Modern rhinoceros species rely on mud wallows for thermoregulation and social interactions, and T. major may have been restricted to wet habitats for similar biological or social reasons.
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Title: Assessing Dinoflagellate Cysts and Geochemical Signals in Surface Sediments of the Northern Bering Sea
Author: Vincy Y Winifred, Vera Pospelova, Evangeline Fachon, Kenneth Neil Mertens and Donald M Anderson
Abstract: Dinoflagellate cysts as well as geochemical parameters were analyzed from 26 surface sediment samples in the northern Bering Sea. Known ocean environmental gradients such as sea-surface temperature and salinity, duration of the sea-ice cover and primary productivity, along with the measured sedimentary geochemical proxies were used to examine the influence of upper water masses on the cyst assemblages. Total concentrations of the organic-walled dinoflagellate cysts vary spatially and range from 726 to 11,673 cysts g-1, with an average of 4,535 cysts g-1. The highest cyst concentrations were observed in the area south of St. Lawerence Island that is influenced by the relatively warm, nutrient-rich Alaska Coastal Current and terrestrial runoff. Well-preserved cysts were recovered in all the samples, with a total of 35 taxa. The cysts of autotrophic Operculodinium centrocarpum sensu Wall and Dale (1966), and heterotrophic Islandinium minutum were the most abundant. Other common dinoflagellate cysts taxa were Spiniferites spp., Spiniferites elongatus, Alexandrium spp., mostly A. catenella and Brigantedinium spp.
Measured sedimentary biogenic silica abundances (% Opal) have consistently higher values (10.7-19.7%) in the area southwest of St. Lawerence Island and lower values in Norton Sound and the Bering Strait. The sedimentary Total Organic Carbon (TOC) measurements range from 0.2 to 1.5%, averaging at 0.6%. The highest TOC values were found in the same area where high biogenic silica values were observed. The spatial distribution patterns of dinoflagellate cysts and the geochemical parameters are complex in the region and influenced by a combination of environmental drivers.
Authors: Niko Deshpande, Jeff Gralnick, Ivan Ishkov
Abstract: Electronic waste (e-waste) is a major environmental hazard, but also a potential source of valuable metals. Traditional methods of metals extraction also present environmental and human health hazards. Shewanella onedensis is an iron-reducing bacterium that has potential applications to metals extraction, as it is capable of using metals as a terminal electron acceptor during anaerobic respiration. In this project, I investigated the application of this bacteria to copper extraction from e-waste. To accomplish this, circuit boards were shredded in a blender for experimental use. Initial metals content was determined using nitric acid digestion and ICP-OES analysis. To test S. onedensis’ ability to survive in contact with potentially toxic e-waste, as well as determine its leaching potential, bioleaching experiments were conducted. This was done by inoculating liquid LB medium with both S. onedensis and crushed e-waste. Despite the lack of noticeable growth, there was a significant decrease in the aqueous copper concentration in the biotic sample. In addition, the cells were found to be viable despite extended contact with e-waste. This shows that S. onedensis is capable of reducing copper from e-waste and could be used to remove that copper from e-waste for mining purposes.
Authors: Diede Hein
Abstract: The rheology of polycrystalline olivine, the most abundant mineral in Earth’s mantle, controls a wide range of geodynamic behaviors, from mantle convection and tectonics, to postglacial rebound and postseismic creep. Rock and mineral physicists develop physics-based constitutive equations grounded in experimental observations to enable modeling and predicting such behavior. Traditionally, these experiments and corresponding constitutive equations have focused on the steady-state creep regime, e.g., the long-term response of a rock to a constant stress or strain rate. The main parameters in these equations include the stress, strain rate, oxygen fugacity, water content, and melt fraction of the rock.
However, recent observations of postglacial rebound and postseismic creep at human timescales cannot be explained by constitutive equations for steady state creep alone, and necessitate a paradigm shift towards constitutive relations that can account for both short-lived transient behavior and long-term steady state behavior. In addition to the aforementioned parameters, expressions for transient behavior often include a parameter called the ‘backstress’, which is related to the elastic interactions between line defects in the crystal lattice that can either enhance or counteract the macroscopic stress imposed on a material. Therefore, quantifying backstresses in polycrystalline olivine is essential to the development of constitutive equations that can predict both transient and steady-state behavior.
This presentation will focus on the rocky road to developing the capacity to perform a variety of approaches that can be used to directly measure or infer backstresses in polycrystalline olivine in the Rock and Mineral Physics Laboratory. I will outline the various types of experiments, their advantages, and the challenges encountered. Some preliminary results and their implications are discussed.
Authors: Keegan Hoffer, Yuchi Zhang, Xinyuan Zheng
Abstract: Oceanic Anoxic Events (OAEs) are periods in Earth’s history characterized by large-scale depletion of aqueous oxygen (O2) from oceans. Some of the notable OAEs identified in the geologic record we are working on include T-OAE (Early Toarcian, ~183 Ma), OAE2 (Cenomanian-Turonian boundary, ~93 Ma). OAEs have been linked to mass extinction events, as well as the formation of the majority of the Earth’s petroleum and natural gas deposits. Mercury concentration in modern marine sediments increases with organic matter content, or total organic carbon (TOC). However, scientific data shows that this positive relationship in marine sediments changes during various OAEs, possibly due to high deposition rates of organic matter. T-OAE specifically may be linked to the Karoo-Ferrar Large Igneous Province (Karoo-Ferrar LIP, ~183 Ma). LIPs are large emplacements in the crust of primarily mafic (basaltic) lava or magma. LIPs are generally associated with increased volcanic activities. Past studies have assumed that high mercury concentrations in marine sediments are directly linked to volcanic activities. We can use the mass independent fractionation (MIF) of mercury isotopes to determine if high mercury concentrations result from LIPs and volcanic activity, or if they are due to re-emission of mercury from older sediments due to changing oceanic conditions. We demonstrated how to measure mercury isotope ratios with MC-ICP-MS.
Authors: Rory Malone, Lindsay Pease, Peyton Loss, Cameron Fleisher, Heidi Reitmeier
Abstract: As corn production moves northward and increases in the Red River Valley of Northwest Minnesota, North Dakota, and Manitoba due to climate change, research is needed on the effects of fertilizer source and rate on nitrogen, phosphorus, and carbon dynamics and the resulting potential water quality impacts. With increased corn production, farmers are implementing fertilization management practices that have not been previously researched in the Red River Valley, which has unique high pH soils. The region is part of the Lake Winnipeg watershed, which is at risk for water quality degradation and eutrophication from excess agricultural fertilizers. A phosphorus fertilizer rate and source trial was established at the Northwest Research & Outreach Center in Crookston, Minnesota in spring 2022 with eight treatments and four replicates. Treatments included monoammonium phosphate (MAP, 11-52-0), MicroEssentials SZ (MESZ, 12-40-0-10S-1Zn), and 25% Struvite (5-28-0) applied at rates for one year and for two years based on crop nutrient requirements. The first year crop rotation (2022) was field corn, and the 2023 rotation will be soybeans. Data were collected for corn grain production, soil nutrient availability (soil carbon, nitrate, phosphorus), and water quality. Soil samples were collected at 0-15 cm and 10-30 cm depth. N-mineralization was collected biweekly throughout the summer field season. In winter 2023, a laboratory trial was established with soils representing the field treatments to examine phosphorus release in submerged samples simulating spring flooding, when nutrient runoff from snowmelt can increase. This research will provide insight on the dynamics of phosphorus in soil and water in Red River Valley soils with different P fertilizer rates and sources. This presentation explores preliminary data from year one of the project.
Authors: Viktor Radermacher, Peter Makovicky
Abstract: The ability to process and digest plant matter has independently evolved countless times among vertebrates. The constraints herbivory places on organisms often necessitates a stereotypical cascade of analogous bauplan modifications between even distantly related groups. While their origins were humble, serving as small but cosmopolitan constituents of Jurassic ecosystems, ornithischian dinosaurs would eventually become the most conspicuous, speciose, and diverse large-bodied herbivores by the Late Cretaceous. Elaborating on the plesiomorphic condition, two ornithischian lineages, Ornithopoda and Ceratopsia, both independently evolved dental batteries. Dental batteries, generally characterised as mosaics of multiple tooth families uniformly worn to produce a single triturating surface, have previously attracted research interest. The ultrastructural refinement of individual teeth of specific derived taxa has been studied, as have rates of evolution of dental characters. However, we still lack deeper insights into the macroevolutionary drivers behind the evolution and refinement of dental batteries. We ameliorate this by devising a novel method quantifying a suite of orodental proxies sampled from species spanning derived and early-diverging members of ornithopods and ceratopsians. Ornithischian dentitions require direct wear to function, so our new method co-opts aspects of the qualitative mesowear and microwear analyses typically used in mammalian systems into a quantitative method appropriate for studying herbivorous, polyphyodont dinosaurs. Using a combination of μCT and laser surface scan data, we quantify the volume of worn dental material as well as the surface areas of the resultant triturating surface in the dentary and maxillary toothrows. These metrics can then be scaled against relevant measures of skull and body size as well as biodiversity, to investigate the macroevolutionary implications of dental battery evolution. We present preliminary results of this method that elucidate the trade-offs involved in individual tooth size, dental battery surface area, masticatory efficiency, and ornithischian diversity and distribution patterns.
Authors: Sanath Aithala, Marc M. Hirschmann, Maria Buss
Abstact: The redox speciation of iron, quantified by the ratio Fe3+/FeT (where FeT= Fe2+ + Fe3+), in magmas affects rocky planets’ geochemical and petrologic diversity by influencing igneous mass transfer processes including crystallization, partial melting, degassing, ascent, and assimilation. Consequently, characterizing Fe3+/FeT variations in martian igneous rocks provides key insights into geochemical evolution on Mars. To constrain controls on Fe3+/FeT in martian magmas, we synthesized glasses similar to the martian basalt, Humphrey, at 100 kPa and 1365 °C in a CO/CO2 gas mix at fO2 spanning ~10 log units (ΔQFM-4.4 to ΔQFM+7) and characterized the glasses’ Fe3+/FeT by Mössbauer spectroscopy at 293 K using extended Voigt based fitting with one hyperfine doublet each for Fe2+ and Fe3+. We find that Fe3+/FeT – fO2 models calibrated from terrestrial melt compositions predict Fe3+/FeT ratios from these experiments accurately. The experiments are consistent with determinations for the martian basalt, Homeplate, but not with a martian-specific thermodynamic model derived from shergottite and nakhlite magmas. Further experiments on other martian compositions and wet chemical analyses will facilitate a comprehensive calibration of Fe3+/FeT – fO2 for martian magmas, and will provide standards for a XANES spectroscopic method to measure Fe3+/FeT in situ in martian glasses.
Authors: Woonghee Lee, Etienne Bresciani and Peter K. Kang
Abstract: The effects of fluid flow on the dissolution of minerals in fractured rock are explored, which is relevant to several subsurface processes such as carbon sequestration, biogeochemical cycling, and karst formation. Fluid flow can create complex structures at the microscopic scale, leading to uneven mineral dissolution and concentration fields. However, most previous studies only focused on 2D systems, leaving the effects of fluid flow on mineral dissolution in 3D systems mostly unknown. To address this gap, we use computer simulations to investigate how fluid inertia impacts the dissolution of calcite minerals in both 2D and 3D systems. We change the fluid injection rate to explore different levels of fluid flow and examine the resulting dissolution rates and patterns. Our results reveal that the dissolution rates vary significantly depending on the injection rate and the dimensionality of the system, leading to unique dissolution patterns. Our results also show that recirculating flows play a crucial role in controlling mineral dissolution patterns. Interestingly, we observe faster calcite dissolution rates in 3D than in 2D for low inertia regimes, but slower rates in 3D than in 2D for high inertia regimes. This study provides new insights into the impact of fluid inertia on mineral dissolution in both 2D and 3D systems, which could inform the design and optimization of subsurface processes and applications.
Authors: Christopher Schuler, Amanda Patsis, Cody Sheik, Cara M. Santelli, Brandy M. Toner
Abstract: Chemical and mineralogical characterization of subsurface environments coupled with thermodynamic modeling will suggest metabolic niches that microorganisms can occupy, while genomic data collected from these organisms highlight their metabolic capabilities and their realized niches. Reduction and oxidation reactions involving iron and sulfur are especially important sources of energy to the anoxic and low-carbon environments of the deep continental biosphere. However, microbially mediated reactions compete with abiotic reactions catalyzed by minerals and aqueous chemical species. We sought to better understand the iron and sulfur cycles in isolated groundwaters within a 2.7 Ga banded iron formation (BIF) in northern Minnesota. Boreholes access fracture networks within the BIF and reach more than 700 m below the surface. We sampled groundwaters flowing from these boreholes and measured major cations and anions to characterize the water chemistry. Additionally, we sampled sediments along borehole walls tens or hundreds of meters into the boreholes. Sediments were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM) and were taken to the scanning transmission X-ray microscope (STXM) at the Advanced Light Source for imaging and C and Fe X-ray absorption near-edge structure (XANES) spectroscopy. Microbial DNA was extracted from filtered borehole waters and borehole sediments; it was processed using a shotgun metagenomic sequencing approach. Metagenomes were probed for genes involved in iron and sulfur cycling. While the water chemistry of both boreholes was similar, the sediment in one borehole contained a mixture of the iron sulfide minerals mackinawite and greigite (reduced iron and sulfur) while the other borehole sediment contained only hematite (oxidized iron) and quartz. We theorize that hematite is oxidizing aqueous sulfide before FeS can precipitate, producing sulfur intermediates which fuel microbial chemosynthesis. Conversely, the sulfidic sediment may act as a sink, trapping both iron and sulfur in less-reactive mineral forms. Imaging of the sediment via SEM and STXM confirmed that microorganisms have colonized these sediments, and analysis of the borehole metagenomes confirmed that the microbial community compositions are statistically distinct. Further analysis of genes involved in sulfur cycling will provide a clearer picture of microbial and abiotic sulfur and iron cycles in the continental subsurface.
Authors: Francesca Socki, David L. Fox
Abstract: Morphological integration and modularity are hypotheses which aim to interpret trait covariation in the context of adaptation. All organisms experience integration amongst traits in some form, with traits covarying due to the need to perform specific functions, meanwhile modularity emerges when some traits become tightly integrated compared to other traits, creating a module(s) that can independently vary. These hypotheses are potentially useful in perceiving how certain clades are able to achieve high morphological diversity and specialization in the context of their diversification history. The rodent clade Geomyoidea is an ideal group for studying integration, given the two families within the clade are ecologically disparate, specialized, and exhibit unique diversification patterns. With a focus on their cranial morphology (given their ecology and phenotypic diversity is highly reflected within their skulls) we performed the following on our dataset: 1) PCAs to assess overall shape variation, 2) based on these results, a hypothesis for the potential modular pattern exhibited by this clade, 3) PLS analysis to determine covariation strength between modules, elucidating potential differences in integration across Geomyoidea. PCAs reveal the majority of variation occurs in the back of the skull, along the tooth row, and along the anterior nasal region. From these results, we hypothesized the Geomyoidea clade to have a 3-module scheme for the crania between the rostrum, the neurocranium/palate region, and the occiput. Across Geomyoidea, however, PLS analyses support a two module scheme separating the occiput from the rest of the crania. Conversely, within each family the greatest support is for our three module scheme. While they exhibit a shared modular pattern, the strength of integration between regions of the crania varies across families. Heteromyidae integration strength is strongly driven by their phylogeny compared to Geomyidae, indicating that geomyid integration patterns may be driven more by environmental or abiotic factors.
Authors: Vincy Winfred, Vera Pospelova, Evangeline Fachon, Kenneth Neil Mertens and Donald M Anderson
Abstract: Dinoflagellates are primarily marine, ecologically versatile single-celled protists with two distinctive flagella and a characteristic nucleus. They are one of the principal contributors to primary productivity in global oceans. Some species of dinoflagellates produce preservable organic-walled resting cysts as part of their life cycle. These cysts serve as a repository for sea-surface conditions of where the primary motile organisms once grew and the sedimentary record. Dinoflagellate cysts are widely used as a proxy indicator for past environmental conditions, with their abundance and species composition affected by sea-surface temperature (SST), salinity (SSS), nutrient loadings, and primary productivity. Here, we present the initial results of an ongoing comprehensive study of dinoflagellate cyst assemblages in the northern Bering Sea.
The Bering Sea serves as an exclusive marine link between the Pacific and Arctic Oceans. It is critical for the transport of nutrients and heat into the Arctic Ocean. Twenty-six surface sediment samples were collected with a Van Veen grab as part of the Distributed Biological Observatory-Northern Chukchi Integrated Survey cruise and were processed using a standardized palynological preparation technique. Our preliminary results revealed diverse dinoflagellate cyst assemblages characterized by taxa commonly found in nutrient-rich coastal waters of the North Pacific, including Operculodinium centrocarpum sensu Wall and Dale 1966, Spiniferites spp., S. elongatus, Brigantedinium spp., and Islandinium minutum. A total of thirty-two cyst taxa were identified, and the estimated total dinoflagellate cyst concentrations varied from ∼1,500 to 7,500 cysts g−1, averaging ∼4,800 cysts g−1. Relative abundances of cysts produced by heterotrophic dinoflagellates are greater in the northeastern part of the Bering Sea, where primary productivity is higher. Analyses of dinoflagellate cyst assemblages and their concentrations, along with known sea-surface parameters, by using multivariate statistical analysis will allow us to identify the main factors controlling cyst distributions and calibrate these microfossils for high-resolution paleoenvironmental reconstructions in the region. Initial observations of environmental variables (e.g., SST, SSS, sea-ice cover, and Chlorophyll-a concentration in the northern Bering Sea show variation throughout the study area.
Authors: Nora Loughlin, David L Fox
Abstract: Examining how climatic factors drive North American mammal diversity gradients is necessary to understand how species assemble. One particularly important aspect of biodiversity is functional diversity, which quantifies how species within a community interact with each other and their environment. As such, analyzing mammalian communities through the lens of functional diversity will provide deeper insight into how these communities may respond to environmental perturbations, such as climate change and biodiversity loss. Our data consist of modern terrestrial mammal taxon lists and a suite of environmental variables representing temperature, elevation, topographic relief, and moisture availability for 1990 grid cells, each 100 km by 100 km, spanning across all of North America. The taxon lists were supplemented with three ecological variables (diet, body size, and locomotor mode) for each of the 749 species in the dataset. Using the FD package in R, we calculated three metrics of functional diversity (functional richness, the number of functional roles represented in a community; functional evenness, the regularity of how species are distributed amongst functional roles; and functional dispersion, the dissimilarity of functional roles) for each grid cell, as well as for null models generated from 1000 randomized taxon lists. We find that observed patterns in functional richness and evenness generally follow those predicted by species randomization, with communities in warmer regions containing a wide variety of ecological niches with a highly uneven distribution of species occupying each niche; and communities in cold and dry environments containing a relatively small number of highly similar ecological niches. We also find that Chiroptera obscure the diversity patterns observed in other taxa due to the similarity of functional roles that chiropteran species occupy as well as the high species richness of this group at low latitudes. These results indicate that functional diversity gradients in mammalian communities are connected to the geography and climate of the continent.
Authors: Chris Hemstad and Katsumi Matsumoto
Abstract: We are developing a steady-state ocean transport model to show how zooplankton preferentially feeds on phytoplankton and smaller zooplankton. Our model will create a more accurate representation of oceanic ecosystems by including two species of phytoplankton and two species of zooplankton. Availability of nutrients such as phosphate, carbon, and nitrogen will be used to determine the Net Primary Production (NPP) of the two phytoplankton species. Current models have shown how one species of zooplankton will preferentially feed on phytoplankton. We will be adding a second zooplankton species to the mix to show how its predation of the smaller zooplankton and of the 2 phytoplankton groups affects the transport of nutrients through the ocean via the biological pump.
Authors: Emma Kostecki, Plinio Jaqueto, and Joshua Feinberg
Abstract: Speleothems are natural recorders of the Earth’s dynamic past. Isotope compositions of speleothem samples show millennial scale changes in processes related to the hydrological cycle and to overlying soil development. In addition to paleoclimate research, speleothems can also be used to understand dynamic processes that disturb the orientation of stalagmites, including seismic events and cave flooding. However, constraining the timing of such events can be challenging, as many stalagmites are not amenable to U-Th dating due to excess thorium associated with high clay contents. In these instances, paleomagnetic methods have the potential to provide a useful means for dating. As stalagmites grow, trace concentrations of magnetic minerals are incorporated into their matrix and are capable of recording the Earth’s magnetic field at the time of formation. The finest grain size portion of this magnetic mineral assemblage is capable of acquiring a secondary, viscous remanent magnetization (VRM). Here, we demonstrate that lab experiments using a laboratory field inside a magnetically shielded room can help us understand the rate at which a particular speleothem acquires a VRM. By applying different initial conditions to the samples, we were able to look at how they affect the rate and strength of acquisition. We’ve found the magnetic mineralogy did acquire a magnetization, similar to that of previous studies and that there is an initial-state, orientation, and time dependence that affects the VRM acquisition. This rate can be used as a tool to estimate when the position of a stalagmite was changed, thereby allowing us to constrain the age of a seismic event or paleoflood.
Authors: Soisiri Charin, Guy Evans, Xinyang Chen, Yanlu Xing, Chunyang Tan, Tianyu Chen, William E. Seyfried, and Xinyuan Zheng
Abstract: Phase separation is a well-recognized process in submarine hydrothermal systems that plays a critical role in the evolution of ocean chemistry. Potassium (K) is among the major cations that are largely regulated by various mechanisms in the hydrothermal system, including phase separation. However, the impact of phase separation on K isotope (δ41K) composition has not been experimentally constrained. Hence, a series of phase separation hydrothermal experiments were conducted in the K-NaCl-H2O system to constrain the K isotope fractionation at 400 °C and 215 to 330 bar. The single-phase starting fluid successfully reached the two-phase boundary using the Ti alloy (Ti-6Al-2Sn-4Zr-2Mo) reactor. The chloride contents of experimental fluid are in good agreement with the theoretical fits suggesting a state of equilibrium. The chemical analysis indicated a preferential uptake of K in the liquid relative to vapor with a partition coefficient (DK/Cl) up to 0.67 at 215 bars, consistent with previous literature. The 41K values of coexisting vapor and liquid retrieved from the experiments range from -0.14 0.05 ‰ to -0.07 0.03 ‰ and -0.02 0.04 ‰ to 0.02 0.06 ‰, respectively. Most vapor samples are isotopically lighter than their coexisting liquid. Due to the distinct difference (up to 0.16‰) between the 41K values of liquid and its vapor counterpart, this study is the first to report that there is a minor, however, significant K isotope fractionation between vapor and liquid at a phase-separated condition.
Authors: Kaylin Brophy, Zsuzsanna P. Allerton and Christian Teyssier
Abstract: Quartzite samples from the Ruby Gap Duplex in Australia were analyzed to determine deformation regimes associated with different levels of deformations. Thin sections made from the quartzite samples were first observed by transmitted-light microscopy under cross-polarized light. Further analysis included backscatter electron (BSE) and electron backscatter diffraction (EBSD) with a scanning electron microscope (SEM) to quantify deformation in terms of degree of crystallographic preferred orientation (CPO) and subgrain boundary rotation (SBR). The results of this project will be used to create an online atlas of well-characterized quartzite microstructures to provide open-source material for educational purposes. Each thin section was analyzed by transmitted-light microscopy to better characterize deformation features within each regime. The least deformed level is regime 1, which occurs at the lowest temperatures and fastest strain rates, and some of its characteristics are patchy and irregular undulose extinction and variance in overall large grain sizes. The intermediate level of deformation is regime 2, present at higher temperatures and slower strain rates than regime 1, and can be identified by obvious core mantle structure, subgrain rotation, elongated and stretched grains, and visible subgrains. The most deformed level is regime 3, which occurs at the highest temperatures and lowest strain rates, displaying irregular grain boundaries, overall small but uniform grain sizes. There are two transitional regimes: regime 1/2 and regime 2/3. EBSD was utilized for quantitative analysis of intra- and intercrystalline orientation.
Abstract: Amanda Patsis, Cody Sheik, and Cara Santelli
Authors: It is well documented that subsurface microorganisms fuel their metabolisms through inorganic sulfur reduction and oxidation reactions. However, organic forms of sulfur are typically overlooked, despite their abundance in biomass and the range of oxidation states they can occupy. Mineralization of organosulfur compounds is an important source of inorganic sulfur species in surface systems; therefore, we hypothesize that it may also play a significant role in biogeochemical sulfur cycling in the deep biosphere. Here, we used a metagenomic and genome-level investigation of 164 unique microbial communities collected through the Census of Deep Life to probe the importance of organic sulfur cycling across the deep-subsurface systems. This robust dataset contains 467 metagenome assembled genomes (MAGs) and spans both marine and terrestrial systems, allowing for a comparison of the metabolic capacity of communities in these two distinct biomes. Assimilatory and dissimilatory inorganic sulfur metabolisms as well as organosulfur assimilation, production, and utilization were prevalent in both marine and terrestrial deep subsurface environments. However, the frequency and proportion of occurrences varied by gene and pathway across the marine and terrestrial divide. While both marine and terrestrial genomes have key organosulfur pathways, terrestrial MAGs have a greater variety of genes, including several that were not detected in marine MAGs. Continued exploration into the scope and scale of microbially driven organosulfur transformation will refine our understanding of deep subsurface biogeochemical sulfur cycling and inform how this impacts broader Earth systems.
Authors: Indigo Davitt-Liu and Xiating Chen
Abstract: Urban trees are widely planted for their aesthetics and their functional benefits (e.g. regulating temperature and hydrology) and recognized as a climate adaptation strategy across the US. However, largely due to the costliness, accessibility, and instrumentation complexity of long-term monitoring, we know little to quantify either the horizontal or the vertical extents of urban tree canopies’ diverse benefits. To understand how urban canopies function with respect to water, we designed and implemented a low-cost, Arduino-based sensing system for urban trees in the City of St Paul. However, we encountered technical difficulties around power regulation which led to sensors being unreliable. We have been working towards improving our sensing system for this upcoming field season. In this poster, we will show an electronic design that will be deployed to measure sap flux in trees. The sap flux sensors operate on the principle of heat dissipation. The sensor supplies a constant temperature through a heater needle inside the sapwood of a tree as sap travels up it reaches another sensor needle. By measuring the difference in temperature at these points and knowing how much heat has been added to the sap through the heater needle, the rate at which sap flows through the tree can be found. This is a proxy for evapotranspiration in trees. This design includes a pair of thermocouple-based sap flux sensors, power regulator for heating the sap flux sensors, and a data logger that records the measured voltage. In this improved circuit, we fixed the power regulation issues that were faced last year which prevented consistent measurements, using low-cost electrical components. A solar panel will also be added as a power source. The sap flux system is designed and made in collaboration with Professor Andy Wickert's Surface Processes Instrumentation Lab. We will also have a prototype of the circuit board available at the poster session. As preliminary results, we will show how well our lab-made sap flux system compares with Dynamax sap flux sensors, an off-the-shelf solution. To do so, we will conduct a hydraulic conductance experiment in the plant growth facility by flushing a known rate of water through two elm and two maple trees, while taking the sap flux measurement.
Authors: Cheyenne Neess
Abstract: Intermediate wheatgrass (IWG) is a perennial cereal grain that is being promoted as a promising crop for regenerative agriculture. The deep fibrous root system of IWG has been frequently hypothesized to improve the structure and fertility of degraded soils. This study investigates how IWG and sustainable management strategies impact soil carbon storage and soil aggregation in agricultural systems. The distribution of permanganate-oxidizable carbon (POX-C) between soil aggregate size fractions was analyzed for four treatment groups: annual crop with climate infrastructure, annual crop with no climate infrastructure, IWG with climate infrastructure, and IWG with no climate infrastructure. Soil samples were sorted into macroaggregate, microaggregate, and silt/clay size fractions using a wet-sieving technique. POX-C was then quantified on the sorted size fractions to compare the relative pools of labile carbon. Preliminary statistical analysis suggests that the climate shelter infrastructure may have a statistically significant effect on enriched POX-C, most prominently in the silt/clay size fraction. This research demonstrates how performing POX-C directly on sorted aggregate fractions can help reveal more subtle changes in carbon storage not revealed with the standard practice of using 2mm bulk samples.
Authors: Jeremiah McElwee, Ikuko Wada, Kazuki Yoshida, Atsushi Okamoto, and Hiroyuki Shimizu
Abstract: Serpentinization is a hydration reaction common in the mantle wedge corner of subduction zones. Because serpentinization is a volume increasing reaction, it can induce stress and cause fracture in the surrounding host rock, increasing the permeability of the host material. In some cases, this can result in a positive feedback mechanism, whereby serpentinization may progress as more fluid is able to flow into the host rock. We investigate the effect of reaction-induced stresses on the propagation of serpentinization in the mantle wedge corner using a 2-D hydraulic-chemical-mechanical model. To accomplish this we use the discrete element method. Serpentinization is modeled as a volume increasing reaction that proceeds as a linear function of the local pore fluid pressure up to a maximum reaction rate. The model domain is set to 5 mm by 5 mm, and the matrix consists of circular disks with 30-60 μm radii. The model is bounded by walls which can move to maintain a fixed confining pressure and background differential stress. The model is initially saturated at a predefined pore fluid pressure, and additional fluids are supplied at the base of the model to mimic the supply of slab-derived fluids. Fluid flow is driven by pressure gradients and occurs via diffusion and along fractures. We test the effects of increasing confining pressure and different background stresses on the reaction feedback during serpentinization.
Authors: Sara Nadian and Joel Barker
Abstract: During the process of firnification that compacts snow into glacial ice, organic and inorganic chemical constituents are preserved in the ice as a stratigraphic record of deposition. As a result, ice cores can provide a time-resolved record of past atmospheric conditions that permits paleoclimatological reconstruction. However, the ability of ice cores to provide a precise time-record of paleoclimates relies on the assumption that identifiable chemical constituents are not displaced after snow deposition and that any stratigraphic structure is maintained. One cause of concern for a disturbance in the stratigraphic relationship between deposition and time is due to potential melt-induced mobilization of chemical constituents within a snow column. Daily or seasonal melting within the snow and/or firn in the accumulation zone of a glacier may result in the mobilization of chemical constituents of interest as meltwater percolates to greater depth, resulting in the destruction of the stratigraphic record. However, the susceptibility of different chemical constituents to become mobilized by meltwater percolation is unknown. Here, we test the hypotheses that a) meltwater percolation does not displace chemical constituents within a snowpack, and b) if mobilization does occur, every chemical constituent is mobilized identically. We use a firn section (14.61-15.67 m) of the Dye 2 ice core that shows evidence of meltwater percolation and refreezing as ice layers (superimposed ice). We focus on inorganic chemical constituents that are commonly used for ice core paleoclimatic reconstruction (SO₄²⁻, F⁻, NO3-, Br⁻, and δ¹⁸O) and dissolved organic matter to determine if solubility is a factor on constituent displacement.
Authors: Irfan Ainuddin, N.A. Jelinski, R. Matamala, C. L. Ping, and J.D. Jastrow
Abstract: Constraining the variability of soil organic carbon (SOC) and total nitrogen (TN) stocks across hillslopes in permafrost-mantled terrain of the low Arctic remains a significant challenge for improving uncertainties in global estimates of permafrost SOC stocks. Despite studies focusing on SOC and TN stocks across regional climate gradients in the northern circumpolar region, the lack of quantitative data across hillslope toposequences introduces large uncertainties in SOC estimates at regional and global scales. Therefore, constraining SOC stocks across permafrost-region hillslopes remains a significant challenge for improving regional and earth system models. We investigated SOC and TN stocks across hillslopes at two locations within a portion of the North American Arctic Transect in the Arctic Foothills of Alaska, USA (Happy Valley and Sagwon Hills). SOC and TN stocks were linearly related (R2 = 0.74) but unlike soils of non-permafrost landscapes, variability was greatest within rather than between hillslope positions. Furthermore, SOC and TN stocks did not generally vary by hillslope position nor were they closely associated with major geomorphic parameters (i.e. slope, curvature) that are typically good predictors of SOC and TN stocks across most landscapes. The landscape processes unique to permafrost features such as ice wedge polygons, non-sorted circles, and water tracks associated with patterned ground along with soil cryoturbation and variation in ice content across these landscapes contribute to the relatively even distribution of SOC and TN stocks among hillslope positions for both sites. This work underscores the need for and importance of local toposequence studies to underpin broader regional-scale predictive efforts.
Authors: Yiwen Lyu and Xinyuan Zheng
Abstract: Illitization is a process by which smectite clay minerals transform into illite clay minerals, which can occur during burial and diagenesis of sedimentary rocks. The fixation of potassium (K) in the interlayer positions and the release of structural magnesium (Mg) are involved in smectite illitization. Modeling shows it is hypothesized that isotope analysis of K and Mg could help to identify the sources of fluids involved in the process, track fluid-rock interactions, and understand the diagenetic environments and histories of sedimentary rocks. The K-Mg isotope fractionations in clays are also controlled by changes in the position of ions within the mineral's crystal structure of these elements during illitization. Here, we provide data on how the K-Mg isotope system behaves in naturally occurring clay minerals from smectite to illite transformation in core and outcrop bentonites from the Denver basin and core bentonites from disturbed belt mountain. These natural samples in which the driving mechanisms of illitization are well understood, are ideal to be studied for the K-Mg isotopic behavior during smectite illitization. The K-Ar ages show that radiogenic argon is well-preserved in the samples and further indicate the primary K isotope signal has a chance to be obtained. Three nanometric size fractions of mixed layer illite-smectite are prepared for K-Mg isotope analysis to observe the kinetic isotope fractionation resulting from the possible dissolution-precipitation process during illitization. In these samples, negative Mg isotope shift and positive K isotope shift with the increased degree of illitization provide insights into the conditions and processes that led to illitization, including permeability (fluid/rock ratio) and chemical and isotope compositions of fluid. The negative correlation between K and Mg isotope composition could also be interpreted as the lower Mg and higher K coordination number in illite minerals. Therefore, the integrated use of K-Mg isotopes is promising to understand the complex processes that control the transformation of clay minerals in natural systems and further reconstruct the geological history of sedimentary basins.
Authors: Abigail Wilwerding, Shanti Penprase, and Andy Wickert
Abstract: The Whitewater River is a tributary of the Mississippi River in southeastern Minnesota. The river morphology was greatly influenced by changes in the level of the Mississippi during the draining of glacial lakes, and the transport of glacially derived sediment. These glacial sediments have distinct chemical compositions that can provide information on the sediment and meltwater sources. A terrace surface near the mouth of the Whitewater is composed of fine red and gray sediments. These are thought to be slackwater deposits, deposited when sediment-laden meltwater from draining glacial lakes flooded the Mississippi and backed up into the tributary, creating a low-energy environment. In this study, we use X-Ray Fluorescence (XRF) to determine the elemental composition of these fine-grained materials at the mouth of the Whitewater River and determine their provenance by comparing this to the composition of previously analyzed glacial deposits. We utilize four Geoprobe sediment cores taken within the slackwater sediments. These sediments have a preliminary age of 11.6 ka based on optically stimulated luminescence dating. Preliminary core description shows fine-grained red and gray sediments suggesting at least two possible provenances for these deposits. They are thought to relate to the late-stage draining of Glacial Lake Duluth and Glacial Lake Agassiz. The elemental analysis of these cores will allow us to directly compare their composition to the makeup of known deposits in the literature, answering critical questions about where the sediment at the mouth of the Whitewater was coming from and understanding drainage organization and glacial behavior at this time.
Authors: Michael Park and Annia Fayon
Abstract: The focus of this project is to develop a workflow using GIS and R methods that will allow for quantitative correlation between microstructural and geochemical datasets. Using these programs, electron backscatter diffraction (EBSD) and electron microprobe analysis (EMPA) data can be correlated to determine instances of peak coincidence providing insight regarding the association of subgrain boundaries and elevated element concentrations. As a case study we used EBSD and EMPA data collected from experimentally deformed apatite. The single crystal was coated in PBZrO3 and deformed in torsion for 5 hours at 300 MPa and 1100 °C to assess the effects of deformation on the diffusion of Pb. Kernel average misorientation analysis from EBSD data and backscatter imaging and chemical data from EMPA for this single crystal show elevated concentrations of Pb along subgrain boundaries. This suggests a strong associated between microstructures and Pb diffusion. To obtain more quantitative results, the color values of each pixel of the images were evaluated against neighboring pixels to detect significant changes in color intensity associated with heightened Pb concentrations and subgrain boundaries. A pattern of significant changes in color intensity was developed for each image and their orientations compared to establish exact correlation.
Authors: Declan Ramirez, Joshua Feinberg, Maxwell Brown, Mara Taft, Kat Hayes, and Ed Fleming
Abstract: As heat-treated artifacts cool their magnetic mineralogy records the Earth’s magnetic field direction and intensity, creating a fixed record that can be used to date the artifact. This project will identify the varieties of ceramic sherds that most reliably record archaeomagnetic data, with factors like time period, ceramic style, magnetic mineral composition, and ceramic type (body or rim) of particular interest. Sherds identified by this project as robust carriers of archaeomagnetic data will be used to construct an archaeomagnetic reference curve for Minnesota (the MARC). The creation of the MARC will increase the quantity and types of archaeological materials that can be precisely dated in Minnesota, making it possible to date nondiagnostic ceramics for the first time, and potentially other heat-treated materials like hearths, fire cracked rocks, and burnt soils. Over time as more dated material is added to the database, the MARC will improve in precision, allowing archaeologists and anthropologists to better place cultural objects in their proper temporal settings. This will lead to a deeper understanding of Indigenous history in Minnesota, and will additionally serve the geomagnetic community by adding mid-continent geomagnetic data to the global geomagnetic database, an area which is currently sparsely covered.
Authors: Anjolie Buzo, Marek Poplawski, Emma Johnson, Jennifer Taylor, Stuart Thomson, Christine Siddoway, and Christian Teyssier
Abstract: Little is understood about how and when glacial incision of the West Antarctic Ice Sheet (WAIS) has altered the topography of Marie Byrd Land (MBL) in West Antarctica. Data from previous studies suggest that the WAIS began to alter the MBL landscape around 34 Ma. However, recent thermochronologic data collected from eastern MBL indicate that the WAIS may have formed as recently as 20 Ma. In order to solve the discrepancy in time of formation, new offshore sedimentary samples have been gathered from MBL. Using sedimentary samples is important because continental rock samples are inaccessible because of large ice sheets. However, sediments that eroded off the continent are accessible offshore. Samples are dated using the radiometric dating method apatite helium dating (AHe) to fill in spatial and chronological gaps with previous AHe and apatite fission track dating. Isolated apatite crystals are shot with specialized lasers to degas all helium present. The gas is then pulled into chambers where it is measured. Once the helium is measured, a date can be calculated. In our research, we have separated the crystals and prepared the samples for AHe. Analysis is ongoing, and we will add the results to existing preliminary data. Preliminary AHe data from offshore-western MBL display ages in the 80-100 Ma range, which is consistent with the breakup of Gondwana. The few samples obtained from eastern MBL display significantly younger ages in the 20-30 Ma range, indicating accelerated exhumation at a time when the WAIS could have potentially formed. Current data efforts will expand the geographic range of detrital sampling in order to pin down spatial and temporal signals of WAIS formation. The data we are helping create can be used to better understand past WAIS formation in the context of tectonics and help predict future responses of glaciers.
Authors: Riley Hollenberg and Joel Barker
Abstract: With global temperatures on the rise, the glacier meltwater flux to oceans, and subsequent sea level rise, is becoming an increasing global concern. 21st century sea level rise from the Greenland Ice Sheet (GIS) meltwater flux is estimated to be within the range of 4 - 27 cm (IPCC, 2019). However, glacier ice melt is not uniform around the GIS and local meteorological conditions influence glacier mass balance. Here, we measure the ice mass lost from select valley glaciers around the periphery of the GIS since the Little Ice Age (LIA), mapping changes in current glacier extent relative to LIA terminal and lateral moraines to identify areas of characteristic trends in glacier mass balance. Glacier change mapping is achieved using processed satellite altimetry data and digital elevation models (DEMs) that are publicly available from the ArcticDEM platform (Polar Geospatial Center, University of Minnesota). Changes in ice volume from the LIA maximum is calculated by reconstructing the paleoglacier surface elevation and area, using the Glacier Reconstruction toolbox (GLaRe) in ArcGIS. We find a general trend of valley glacier retreat around the GIS periphery in agreement with published data. However, glacier volume loss variations are observed up to an order of magnitude, dependent on the size of the glacier, equilibrium line elevation, and proximity to warm ocean currents, which highlights the influence of local conditions on background global climate warming.
Authors: Viven Sharma and Ikuko Wada
Abstract: We investigate the effects of plate coupling force, topography, density variation, and slab geometry on the distribution of stress in the forearc region of subduction zones, using 3-D numerical models. The plate coupling force depends on the strength and the down-dip width of the subduction fault and the normal stress on the fault, and it generally induces horizontal compression. On the other hand, the surface topography of the forearc results in its tendency for gravitational collapse, which causes horizontal tension that competes with the plate coupling force. Previous studies indicate that subduction faults are generally weak, with the effective coefficient of friction of < 0.05 for most subduction zones, resulting in horizontal tension in the inner part of the forearc due to gravitational collapse in some subduction zones. Geophysical observations indicate that the mantle wedge corner beneath the inner forearc of some subduction zones is serpentinized, causing lateral variation in density. Down-dip and along-margin variations in slab dip also affects the plate coupling force, leading to spatial variation in the state of stress in the forearc. The effects of such density variation and slab geometry on forearc stresses have not been quantified. We use a simple model geometry and incorporate a serpentinized mantle wedge corner as part of the overriding lithosphere and examine how the stress distribution in the forearc varies with the strength and the width of the subduction fault, surface topography, and the degree and the extent of mantle wedge serpentinization.
Authors: Allison DeCou, Allison DeCou and Joel Barker
Abstract: Glaciers export dissolved organic matter (DOM) to downstream ecosystems in meltwater. A stream’s DOM pool is influenced by input from surrounding soils and vegetation whereas glacial meltwater has the addition of glacially-derived DOM to the bulk DOM pool. Current data availability studying DOM in glacial streams is largely limited to polar and mid-latitude glaciers as studies of DOM content of equatorial glacier-fed streams are extremely limited. Here, we use fluorescence spectroscopy to characterize how the optical properties of dissolved organic matter evolve along a glacial stream that flows from the Hermoso glacier on Volcan Cayambe, Ecuador. Results show that DOM characteristics change as the meltwater flows from higher elevation pure glacier meltwater to lower elevation streams that flow through different types of vegetation cover. Specifically, the DOM evolves from protein-like and microbial-like near the glacier terminus to more humic-like downstream near the vegetated area of the watershed. The transformation from protein-like to humic-like prior to the establishment of developed soils suggests that in-stream biogeochemical processes involving dissolved organic matter are occurring and that glaciers play a crucial role in providing DOM to aquatic ecosystems by stimulating the aquatic carbon cycle.
Authors: Jamison Ward, Kyle Dayton, and Esteban Gazel
Abstract: Northwest Africa 2737 (NWA 2737) is a chassignite belonging to the SNC Martian meteorites. Based on its olivine cumulate nature and high Mg content, NWA 2737 is a dunite consistent with crystal accumulation due to fractional crystallization of a primitive basaltic magma. Fluid and melt inclusions trapped within the meteorite’s primary minerals can preserve information about the magma from which NWA 2737 crystallized, helping to constrain Mars’ mantle sources and volatile budgets. Here, Raman spectroscopy was used to probe the mineralogy and geochemistry of fluid and melt inclusions in a thick section sample of NWA 2737. Additionally, a novel combination of Fourier-Transform Infrared spectroscopy and Raman spectroscopy was employed to rapidly evaluate the modal mineralogy of NWA 2737 compared with EDS mapping methods.The analyzed sample of NWA 2737 had a modal composition of 85.3% olivine, 5.3% orthopyroxene, 3.7% clinopyroxene, 3.6% chromite, and 2.0% feldspathic glass. Raman spectra of major phases indicated that olivine, orthopyroxene, and chromite are all Mg-rich while clinopyroxene had compositions ranging from diopside to augite. These data reaffirm the olivine cumulatic nature of NWA 2737. Raman analysis of melt inclusions hosted in olivine revealed the presence of daughter phases containing C, P, and S, including dolomite, magnesite, apatite, and anhydrite. Apatite precipitation may have resulted from phosphorus saturation in the melt phase due to the crystallization of the surrounding olivine host. Although no sulfide inclusion phases were identified in this study, oxidation of the parental melt would have eventually induced sulfate saturation in melt inclusions, promoting the precipitation of sulfate minerals such as anhydrite. Alternatively, anhydrite could be an alteration phase as found recently on Jezero Crater. Carbonates were likely precipitated as in situ immiscible phases within melt inclusions or by a secondary reaction of a CO2 fluid phase with the olivine host or high-MgO glass. Although no CO2 peaks were observed in Raman spectra of fluid inclusions, the presence of carbonate daughter phases in melt inclusions testify to high CO2 content in the parental melt. Overall, the identification of carbonate and sulfate phases in NWA 2737 melt inclusions supports the notion that the parental magma was enriched in volatile elements such as C and S.
Authors: Liyang Qin, Vera Pospelova, and Vincy Winifred
Abstract: Biogenic silica (BioSi) in sediments is an indicator of siliceous production (primarily by diatoms) and depositional processes influencing its distribution in the Arctic Ocean. In this study, we investigated the spatial distribution of BioSi (%OPAL) in surface sediment from the eastern Chukchi Sea and Alaskan Beaufort Sea to improve our understanding of BioSi deposition and controlling deposition factors in the Arctic region. A total of 69 surface sediment samples were collected during the 2018 and 2019 research cruises (HLY1801, HLY1803, HLY1901 and NBS2019). All samples were stored in the dark at 4°C until processes for analysis in the fall of 2022. All samples were desalted, freeze-dried and hand-powdered prior to chemical dissolution for geochemical measurements. A set of 30 samples from the eastern Chukchi Sea was measured for BioSi at the Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia (UBC), and the rest of the samples were analyzed in the Paleoenvironmental Laboratory at the University of Minnesota. The determination of BioSi in the surface sediments followed the standardized UBC protocol based on Mortlock and Froelich (1989).
Our results show that BioSi sedimentary content is greater in the eastern Chukchi Sea (from 2.3% to 19.3%) and comparably lower in the Beaufort Sea (from 1.8% to 3.7%). Sites with the highest BioSi values (~10.9-19.3%) are from the northern part of the studied Chukchi Sea. Sites with the lowest measurements (averaging ~2.5%) are in the nearshore area of the Alaskan Beaufort Sea. The initial analysis reveals that the relative abundance of BioSi in surface sediments increases in the offshore direction in the eastern Chukchi Sea. It also indicates the complex spatial distribution of BioSi in the surface sediment. Our data are in agreement with previously published regional studies that suggest that the relative abundance and distributional patterns of BioSi are influenced by multiple factors, including upper water column primary production, ocean circulation, terrigenous sediment input, and sea ice cover, among other factors. Currently, the environmental data compilation and a detailed study are underway.
Mortlock, R. A., & Froelich, P. N. (1989). A simple method for the rapid determination of biogenic opal in pelagic marine sediments. Deep Sea Research Part A. Oceanographic Research Papers, 36(9), 1415–1426.
Authors: Rashida Doctor, Joshua Feinberg, and Plinio Jaqueto
Abstract: Speleothems are an attractive material for investigating fine scale paleosecular variation of the magnetic field because of their quick growth rate, resistance to alteration, and ability to be dated using 234U-230Th geochronology. Similar to continuous sedimentary deposits, speleothems have been used as archives of paleomagnetic behavior, yet questions still remain about the mechanics of remanence acquisition. Remanence acquisition in stalagmites and flowstones is unique compared to other classic paleomagnetic materials: a trace amount of detritus (including magnetic material) is delivered to speleothems via drip water, grains rotate into statistical alignment within the thin film of water atop of the speleothem, and their magnetization is immobilized by an actively crystallizing carbonate front. Numerous studies have shown that speleothems can faithfully record field directions, at least along the vertical growth axis. However, the ability of an actively crystallizing matrix to accurately record field intensity has not been characterized. Our artificial speleothems aim to capture the process of detrital magnetic minerals falling through a water column, interacting with a highly textured surface, and being encapsulated as a matrix crystal grows up and around it. We recreate this environment using the fast-growing crystal, ammonium dihydrogen phosphate (ADP), precipitating out of solution in controlled magnetic field conditions. Commercial magnetite powder was suspended in the solution and incrementally pipetted over the growing crystal matrix. A positive non-linear relationship was observed between field intensity and remanent magnetization for Earth-like fields (between 15 and 70μT). Ongoing studies involve adding the clay mineral kaolinite to the solution to increase flocculation and more accurately represent the mix of detritus in natural speleothem.
Authors: Charles Soucey, Peter K Kang, E Calvin Alexander, Chloe Fandel, Crystal Ng, Tony Runkel, and John Barry
Abstract: Nitrate contamination is a pervasive problem in the karst aquifers of SE Minnesota where over application of fertilizer leads to a buildup of nitrates in the subsurface rock matrix. Because of the dual porosity present in karst systems (matrix and solution enhanced conduits) groundwater contaminants can travel great distances over short time intervals once they enter the conduit network. These nitrate contaminants can also become engrained in the rock matrix, where they can diffuse into conduits and feed springs for extended periods of time, even without active precipitation. This nitrate mobilization is further complicated when considering a mixture of areal recharge via percolation and direct recharge entering conduits via sinkholes. Our research aims to clarify the karst transport dynamics of excess nitrates in relation to recharge events such as precipitation and snowmelt by studying Bear Spring, a perennial spring in the Galena group karst system of SE MN. By combining high resolution spring monitoring techniques with dye tracing, stable isotope analysis, and discrete conduit modeling, we can assess how surface recharge interacts with the karst groundwater system. We introduce the concept of a bedrock nitrate gradient produced from repeated fertilizer applications and matrix infiltration combined with periodic flushing of nitrates stored in the conduit network. This framework is investigated as a plausible explanation for nitrate concentration dynamics observed at Bear Spring by analyzing field data and constructing numerical models using MODFLOW-CFPv2, a software package developed for modeling flow and transport in conduit networks and sinkhole-spring systems.
Authors: Owen Wold and Xinyuan Zheng
Abstract: Isotopic analysis of potassium in natural samples can improve understanding of the global potassium cycle, which can be used as a proxy for the carbon cycle and, as a result, climate change. In particular, the flux of K in hydrothermal vent systems is poorly constrained. Altered basaltic rock in these systems is very low in K, and current methods are unable to remove matrix elements from samples sufficiently, introducing significant error in measured 41K/39K ratios. This study aims to develop a new method of column chromatography by which potassium can be more effectively isolated. The behavior of K and other elements under different conditions was analyzed, including testing the effects of varying ion-exchange resins, columns lengths and diameters, and combinations and molarities of hydrochloric and hydrofluoric acid. Elemental makeup and isotopic ratios of samples were analyzed on the Nu Plasma MC-ICP-MS and triple-quad ICP-MS. The results of this study show promise for a method of single-pass column chromatography that can effectively isolate potassium, as well as lithium, allowing for high-precision analysis of low-K samples in the future.
Authors: Lila Roach and Grant Goedjen
Abstract: By evaluating the fate of neonicotinoid insecticides and fipronil through conventional wastewater treatment plants. Possible strategies for removing insecticides in the wastewater treatment process can be developed. However for this to occur the manner in which the insecticides pass through the treatment plants needs to be determined. In order to do this a lagrangian mass balance approach is being used to track where the insecticides enter the plant and where they leave be this via liquid or biosolids. Solid phase extraction procedures are used in order to extract the insecticides being analyzed and remove any matrix interference, in addition, all samples are spiked to track present recovery. Once all samples have been extracted and then reconstituted they are passed through a liquid chromatography-tandem mass spectrometer to be analyzed. As of now, it has been found that insecticide concentrations increased from influent to effluent in the liquid samples. This increase from the influent to effluent may be due to the partitioning that occurs within the wastewater plant transferring the pesticides present in the solid sample into the liquid ones. It may also be possible that the increase seen between the influent and effluent samples is due to the reduced matrix interference in the effluent samples.
Authors: Azucena Sierra Garcia, Kyungsoo Yoo, and Julie Grossman
Abstract: Management practices and topography, particularly in mountainous regions, have a direct influence on the amount of soil organic carbon (SOC) and total nitrogen (N). In mountain agroforestry coffee systems where farmers frequently co-produce other important foods like maize, bananas, mushrooms, honey, and meat, reestablishing the balance between soil health and mountain agriculture is particularly important. Although agroforestry coffee systems assert to be significant diversified farming systems that offer smallholders ecological, economic, and social benefits, their combined effects with topography on SOC and nitrogen, particularly in mountain coffee, are still unknown. This study examines the effects of slope position and management on soil carbon and nitrogen on small coffee farms in Huatusco, Veracruz, Mexico. Soil samples were collected from two different slope positions (erosional and depositional) and three coffee systems (traditional polyculture (TP), organic traditional polyculture (OTP), and specialized monoculture with Inga (S-Inga) in each position. The findings demonstrated that soil carbon and nitrogen levels were significantly influenced by management, with higher levels being found in organic, traditional polyculture systems. The fact that the effect of slope positions (erosional vs. depositional) did not have a significant effect on SOC and nitrogen demonstrates the beneficial role that shaded trees played in the coffee systems.
Landscape Evolution in Marie Byrd Land, West Antarctica
Jennifer Taylor, Fiona Swope, Christine Siddoway, Stuart Thomson, Christian Teyssier
Ice sheets and the landscapes they inhabit are mutually dependent on one another. Landscapes influence how and where ice sheets can form, where ice will flow, and the overall stability of the ice sheet. At the same time, flowing ice can change the landscape by carving deep glacial valleys, eroding massive quantities of rock and sediment, and causing the Earth’s crust to adjust to the weight of the ice. Much of the landscape beneath the West Antarctic Ice Sheet (WAIS) is below sea level, making the WAIS less stable and more susceptible to warm seawater and potential collapse. Models of how the WAIS might behave in the future need to incorporate the present-day subglacial landscape. These models are often tested and validated using what we know about how the WAIS behaved in the past. However, many key aspects of the history of the WAIS, including the timing of WAIS formation, are still debated or unknown, limiting the usefulness of ice sheet models. Past landscape evolution can be characterized using low-temperature thermochronology, investigating the thermal histories of rocks that cooled as erosion brought them to the surface. In this study, we use cooling histories preserved in the rock record along with thermal models of the Earth’s crust to characterize landscape evolution in Marie Byrd Land (MBL), West Antarctica, over the past ~80 million years. Preliminary models utilize a suite of new and existing thermochronologic data from across MBL and investigate the timing of initial WAIS glacial incision, the magnitude of erosion and exhumation through time, and the thermal state of the crust. Initial results suggest MBL is subdivided into regions with distinct exhumation histories, but a variety of landscape evolution scenarios can reproduce the currently available data. Ongoing efforts will expand these datasets to cover more of the MBL landscape and refine model scenarios to better characterize landscape evolution through time.
Impacts of Low-Temperature Alteration on Subsurface Ecosystems
Christopher Schuler, Brandy M. Toner, Cara M. Santelli
The continental crust is one of the largest microbial habitats on Earth, but fundamental questions about the distribution of subsurface life forms and their interactions with their environment remain. The majority of microbial life in these environments is found in thin biofilms on the surfaces of fractured rock networks. By describing the mineralogy of these surfaces in fine detail, we sought to better understand the geochemical evolution of these environments and explore how subsurface lithology might influence microbial life. Thin sections were prepared from rock cores extracted from the Soudan Underground Mine State Park. These cores intersect a 2.7 Ga banded iron formation in northern Minnesota, a site known to contain an active microbial community. Samples were chosen from areas containing exposed fracture surfaces as well as mineralogy conducive to microbial life. These samples were described using optical microscopy and scanning electron microscopy; they were also taken to the X-ray fluorescence microprobe at the National Synchrotron Light Source – II. Analyses of the thin sections showed that the bulk of these cores contained rock unlikely to offer either nutrients or energy sources to subsurface microbes; however, some areas contained “hot spots” likely to be major drivers of microbial life. Additionally, these areas seemed to be more geochemically active, as determined by the dissolution of primary phases and the presence of secondary or alteration minerals. These results suggest that life in the continental subsurface may be distributed in a markedly uneven manner; the density of subsurface microbial life may be highly dependent on the availability of life-supporting minerals.
Jabari Jones, Lucy Andrews, Jessica Balerna, Vincent Chireh, Jenny Rempel, Nada Saidi
The implementation of stream restoration projects is complicated by many factors. These include physical factors such as the size of the river and the climate, as well as social and economic factors like political willpower and available funding. Many studies have investigated the physical results of restoration projects (for example, did more fish survive after the project?), but few studies have tried to understand where stream restoration projects happen. In particular, few projects have tested whether stream restoration siting is associated with racial and economic disparities.
We use a paired analysis of restored sites and control sites, matched using a suite of biophysical data, to understand where stream restoration happens and what the surrounding communities look like. Our initial results suggest relatively equitable siting of restoration projects in a database from the California Department of Fish and Wildlife Restoration Grant Program, with respect to household income and racial demographics. In the future, we intend to expand the datasets that we are considering to examine different funding structures and geographic locations. As society wrestles with complex challenges like disinvestment and green gentrification, it is crucial to understand where and for whom restoration happens.
Lindsey Kenyon, Ikuko Wada
As oceanic tectonic plates subduct, they drag the overlying mantle material, inducing mantle flow in the overlying wedge-shaped region of the mantle. Where the subduction direction is oblique to the subduction margin, the mantle wedge flow pattern is three-dimensional. Flowing mantle causes the mineral crystals, mainly olivine, to align in the flow direction, resulting in the development of crystal preferred orientation (CPO) and anisotropy in the elastic properties of the mantle. This causes seismic shear-wave waves to split into two components that travel at different speeds, resulting in shear wave splitting (SWS), which is characterized by two parameters: the fast direction and the delay time. Simplifications to the elastic anisotropy of the upper mantle has been made in some previous studies, potentially impacting the SWS parameter calculations. In this study, for a given 3-D mantle wedge flow pattern, we calculate the full and simplified elastic anisotropies in the mantle wedge for four types (A-, B-, C- and E-type) of olivine CPO and calculate SWS parameters with both the full and simplified anisotropies. We find that relative to the full anisotropy, simplified anisotropy has modest effects on SWS parameters except that it causes smaller delay times for C-type CPO, which can lead to underestimation of elastic anisotropy. In general, with either anisotropy, A-, C- and E-type CPO result in fast directions that are close to perpendicular to the margin, similar to the fast directions expected from 2-D flow.
Archaeomagnetic Investigation of Soil Profiles at Lake Benton, Minnesota
Mia Schwartz, Joshua Feinberg, Maxwell Brown, Edward Fleming
Lake Benton is located in Lincoln County in the far southwestern corner of Minnesota and formed shortly after the last deglaciation. Although relatively shallow (max depth ~9 m), the lake has been a permanent landscape feature for the last 12,000 years. The lake hosts a small, privately-owned island that contains one of the most important archaeological sites in Minnesota, where artifacts show that the site was inhabited by different cultures for at least the last 10,000 years. Questions remain about how the site was used during different periods and if the site experienced abandonment. Here we use magnetic methods to explore the occupational history of the island. Magnetic minerals have the unique ability to serve as indicators of human activity. Magnetite (Fe3O4) and other magnetic minerals are notably enriched in anthropogenic soils because human-driven processes, such as the processing of food and burning of wood, can result in their crystallization. To better understand the history of Indigenous occupation at Lake Benton, we analyzed the magnetic susceptibility and magnetization of soils from four vertical profiles on the island. Two of the profiles are sited on a fire feature, and the other two are located in an area with two meters of stratified refuse. Magnetic susceptibility measurements show a clear peak associated with the center of the fire feature, consistent with earlier work on hearths elsewhere in the world. Further rock magnetic measurements will allow us to determine whether the magnetic mineralogy and magnetic grain size distribution differs appreciably from that of adjacent soils. The chronologic correlation of magnetic minerals in relation to the soil horizonation for all four profiles will allow us to develop a more comprehensive history of Indigenous habitation on this island, and perhaps a greater understanding of Minnesota’s history. This work is occurring in consultation with the Prairie Island, Lower, and Upper Sioux Indian Communities.
Metagenomic insights into the importance of organic sulfur in the deep biosphere
Amanda Patsis, Cara Santelli, Cody Sheik
Mineralization of organic sulfur is an important source of oxidized and reduced sulfur compounds in low-sulfate environments such as modern freshwater systems and the Archaean ocean. Thus, we hypothesize that organosulfur also plays a significant role in the biogeochemical cycling of sulfur in the nutrient-deprived deep biosphere. To investigate this question we mined shotgun metagenomic datasets from a deep, terrestrial subsurface environment at Soudan Underground Mine, MN. Legacy boreholes in Soudan Mine reach over 800m below the surface and transect a Neoarchaean (~2.7 Ga) massive hematite iron formation, providing access to the fractured rock aquifer below the mine. The conditions in this aquifer resemble Archean oceans, with reducing, anoxic brines that have sulfate levels much lower than present day oceans; thus, this setting provides a useful analog to the oceans on the early Earth. Our Metagenome Assembled Genomes (MAGs) show evidence of both assimilatory and dissimilatory sulfur metabolisms. Over 77% of MAGs have one or more genes involved in the degradation of cysteine to sulfide, and over 65% have a sulfur dioxygenase (sdo) gene to produce sulfite from S-sulfanylglutathione. The cryptic cycling of organic sulfur may be a previously overlooked source that is key to refueling dissimilatory sulfur metabolisms in this highly oligotrophic setting. Additionally, 93% of MAGs contain an incomplete sulfur assimilation pathway. Since sulfur assimilation is necessary for life as we know it, this could indicate the importance of inter-organism interactions and metabolic handoffs in deep subsurface communities. Further examination of organosulfur assimilation, production, and utilization pathways will improve our understanding of biogeochemical sulfur cycling in the deep terrestrial biosphere and may have implications for our understanding of the evolution of life in Archaean oceans.
Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the Alaskan Arctic
Vincy Winifred, Vera Pospelova, Evie Fachon, Donald M Anderson, Kenneth Neil Mertens
Global environmental changes either due to anthropogenic activities or natural variability affect marine phytoplankton, including dinoflagellates. Approximately half of the dinoflagellates are heterotrophic, whereas the other half are autotrophic or mixotrophic. Loss of sea ice cover, nutrient availability, fluctuations in sea-surface salinities and temperature are some of the factors that affect the distribution of dinoflagellates. Around 13 to 16% of living dinoflagellates produce organic-walled resting cysts as part of their life cycle. The resting cysts are resistant to dissolution, unlike calcareous or siliceous microfossil as they are composed of refractory organic matter called dinosporin. The current study investigates the effect of present-day environmental conditions on dinoflagellate cyst distribution across the Alaskan-Arctic. Ninety-one surface sediment samples collected during expeditions in 2018 and 2019 is being processed using a standardized cyst extraction technique. The cysts will be identified and counted, and their variations from distal to coastal sites will be determined. Here, we present our initial results on abundances and spatial distributions of dinoflagellate cysts, including those produced by harmful species in the Alaskan Arctic.
Investigating Food Sovereignty at the White Earth Reservation
Ella Rodewald, Mia Schwartz, Rawan Algahtani, Anjali Muppidi, Diego Juarez
Food sovereignty is defined as a food system centered around self-determination, equal access, and sustainability, and is a movement instrumental in addressing the global grand challenges of food security and equity. Funded by the Healthy Foods, Healthy Lives Institute, a collaborative team of administrators, faculty, and students from the White Earth Tribal and Community College (WETCC) and the University of Minnesota–Twin Cities and Crookston campuses are working together to develop a community-engaged and informed WETCC Food Sovereignty Action Plan. Our cohort is compiling information on Indigenous and traditional foods into a systems map, which we plan to use as an educational tool at conferences and in other academic settings. Upon completion, we hope this map can assist in the development and implementation of a food sovereignty plan for the White Earth Reservation, supporting a more economic, accessible, and sustainable food system for the entire community. We are contributing to the creation of the food systems map by investigating the social, economic, and environmental contexts of a traditional Indigenous meal. Our understanding of the ingredients will be supported by two complementary approaches: conversations with community members and food sovereignty advocates, and conducting a comprehensive literature review. Our conversations have answered questions about food sovereignty and its implementation from how harvesting and hunting methods have been impacted in recent years and how the White Earth community has addressed food insecurity. By understanding the acquisition, usage, and significance of each ingredient in this meal, we hope to gain insight into specific needs of the White Earth community and their food system. Our end goal is to understand stakeholders’ perspectives on the policy, traditions, cultural significance, and access to these ingredients, and ultimately the ability to create these dishes in the White Earth community today.
Characterizing and quantifying the distribution of dissolved organic carbon in the snowpack over Lake 2, Carver Park Reserve, Minnesota.
Jacqlyn Cronson, Joel Barker
Snowpacks on top of a frozen lake contain reserves of organic matter (OM) deposited from the atmosphere and produced in situ by microorganisms. The spatial distribution and molecular characteristics of this OM pool may change over time with snow metamorphosis. When the snow melts, this OM pool is mobilized and represents a potentially important input of nutrients to the lake following lake ice melt. This input occurs prior to maximum primary productivity during summer and may serve as an important pulse of nutrients in the early melt season. However, this source of OM remains poorly constrained and its function as an early-season nutrient source is unknown. This study quantifies a snowpack-derived OM input to a rural lake in Carver Park Reserve, MN, by quantifying OM as dissolved organic carbon (DOC), and by describing its molecular characteristics by fluorescence spectroscopy.
Snowpack OM is characterized by protein-like fluorescent moieties that suggest a labile source of nutrients for lake biota. While the concentration of snowpack-derived DOC is lower than the concentration of DOC in the lake water column, it is a significant source of OM-derived nutrients early in the ice-free season that may stimulate microbial metabolic processes.
Cranial description of a new basal sauropodomorph from the Early Jurassic of Antarctica
Lynnea Jackson, Peter Makovicky
Basal sauropodomorphs, formerly ‘prosauropods’, are a paraphyletic clade of animals that make up the precursors to true sauropods. These non-sauropod sauropodomorphs arose during the Late Triassic and diversified in taxonomy and morphology throughout the Early Jurassic until their extinction at the Early/ Middle Jurassic boundary. Early species were omnivorous and bipedal and developed obligate herbivory and quadrupedalism in more derived species. Basal sauropodomorphs achieved a global distribution during their reign, including occupation at high latitudes. Here, I present a description of the cranial anatomy of a new species of basal sauropodomorph from the Early Jurassic of Antarctica. Basal sauropodomorphs are well-known throughout Gondwana, especially in southern regions of South American and Africa, however, the fossil record of Antarctica is severely understudied by comparison. Only one other basal sauropodomorph is known from Antarctica, Glacialisaurus hammeri, although it is only described from hindlimb remains. This new specimen, FMNH PR3051, represents the first cranial description of a basal sauropodomorph from Antarctica. Preliminary results suggest that FMNH PR3051 is more closely related to North American and South African species and more derived than Glacialisaurus. The skull is mostly complete apart from a missing dorsal margin and partial braincase and it is mediolaterally compressed and sheared obliquely. FMNH PR3051 is unique in that it has unserrated teeth and a nasal that is a thin sheet of bone with a fold along the dorsal margin but no frontal ramus. It was an herbivorous animal with a ‘V’ shaped skull. I am reconstructing the skull using computed tomography (CT) segmentation to create a digital model of each preserved skull bone. I will perform a phylogenetic analysis on this specimen and reconstruct Early Jurassic Gondwanan biogeographic patterns of basal sauropodomorphs.
Nora Loughlin, David L Fox
Previous studies analyzing North American mammalian diversity have revealed the presence of a latitudinal taxonomic diversity gradient, however comparatively little research has examined the functional diversity of North American mammalian communities. As a metric of ecosystem function, functional diversity may provide a more nuanced understanding of these communities and their resilience to ecological disturbances. We quantified three metrics of functional diversity (functional richness, functional evenness, and functional dispersion) across the continent in order to determine their relationships to geography and climate. Our data consist of terrestrial mammal taxon lists, elevation, topographic relief, and several climatic variables representing temperature and moisture availability for 1990 grid cells from Canada to Panama, each 100 by 100 km. For each of the 749 species in the dataset, we recorded three ecological variables: size based on log10 of body mass in grams, diet, and locomotor mode. We then used the FD package in R to calculate each functional diversity metric for each grid cell. We find that functional richness increases with decreasing latitude and increasing temperature and moisture availability; functional evenness is high at high latitudes and low at high elevations and where moisture availability is high; functional dispersion is high in grid cells with high elevation and relief, and at its highest in grid cells with moderate and high temperature and moisture availability. These results indicate the presence of functional diversity gradients related to the latitude, topography, and climate of North America.
Deforming Pyroxene and Olivine in Compression to Establish the Mechanism of Mineral Mixing at Plate Boundaries
Maisy Waech, Lars Hansen, Amanda Dillman, and Harison Weisman
The theory of plate tectonics is a paradigm of Earth science, and it provides a theoretical link among many of Earth’s processes. Serval major aspects of plate tectonics, such as plate boundary formations, explain the existence of volcanoes, fault lines, and the formation of new continental crust. For instance, in order for a new plate boundary to form there must be a localized weakness in Earth’s lithosphere, which would lead to subduction or transform fault formation. There is consensus that a key feature of plate boundaries shear zones is a fine-grained mixture of multiple phases, which are weaker together than when separate. Several models exist to try and explaining this mixing, and previous work has focused on phase mixing of olivine and orthopyroxene in torsion. Unfortunately, these previous experiments cannot distinguish between these mechanisms of mixing. To overcome these ambiguities, I am examining the initiation of phase mixing in a simpler deformation geometry. Samples were created as a layered aggregate of orthopyroxene and San Carlos olivine. This sample was then placed in a high temperature gas medium apparatus and deformed in compression to 50% strain. Investigating the interface at the boundary between opx and olivine layers will help to distinguish between models of mixing, which will help improve our understanding of plate boundary process.
Impacts of glacially-driven base level change on river channel long profile across timescales: Whitewater River, southeastern Minnesota
Shanti Penprase, Wickert, A.D., Larson, P., Dunn, C.N., Bezada, M., Running, G.L., Faulkner, D.J, Jones, J. and Schewe, J.
The channel long profile of a river reflects the response of that river to changing boundary conditions and the relative balance between the river and these environmental factors. Base level, or the water level at the mouth of a river, is one of these many boundary conditions and can have dramatic impacts on river channel long profile. Relative base-level rise for a river system results in increased deposition and shallower slopes. A fall in base level results in incision, steeper slopes, and, in detachment-limited rivers, a convex knickzone can form. For tributary rivers, this base level is set by the mainstem river they flow into.
In glaciated regions, water and sediment supply coming off the ice front can dictate bed elevation and water level. In Minnesota, the Mississippi River (MR) was long impacted by glacial signals coming from the Laurentide Ice Sheet (LIS) and, as a result, the base level of MR tributaries during periods of glaciation was directly linked to glacial cycling.
In this study, we examine the channel long profile response of the Whitewater River (WR), a tributary to the MR in southeastern Minnesota, to changes in the LIS and variable base level on the MR to understand the impacts of glaciation on tributary systems. We first reconstruct the now-buried bedrock long profile of this river using depth to bedrock and seismic refraction data. We hypothesize that this bedrock paleochannel was active during integration and incision of the MR (between 0.8-2.5 Ma). We then reconstruct the profile of the WR during and after the Last Glacial Maximum using preserved fluvial terraces along the modern river valley. Finally, we link these two channel long profile morphologies and the modern river system to changes in the LIS to demonstrate how this tributary system was impacted by glacially-driven changes in base level. In so doing, we demonstrate the impacts of glaciation on not just rivers directly connected to the ice front, but on the entire fluvial network.
Investigating Whether Soil Health Management Systems (SHMS) increase field working days and farmer quality of life
Bailey Tangen, Anna Cates, Jeff Vetsch, Bill Lazarus, Emily Krekelberg, Gregg Johnson
Field operations must be performed at the correct water content to minimize soil structural damage. Timing operations such as planting and tillage is becoming more challenging due to irregular and higher intensity precipitation in the Upper Midwest associated with climate change. The mechanism for rain delays is that rain destroys macroaggregates and decreases macropores, which induces waterlogging at the surface, so field equipment compacts wet soil. Over time, compaction reduces water infiltration and productivity. Farmers claim that lower soil disturbance associated with Soil Health Management Systems (SHMS) is expected to increase infiltration and protect soil structure, which may allow these systems to withstand field traffic sooner than conventional tillage systems. To evaluate this claim, we investigated the response of soils to rainfall under different management systems. During the 2021 growing season, moisture content and soil aggregate distribution were monitored at 3 on-farm pairs representing conventional and SHMS in southern Minnesota and at Southern Research and Outreach Center in Waseca, MN. Initial results will be presented: Aggregate stability from wet aggregate sieving, potentially mineralizable carbon, and volumetric water content (VWC). Preliminary results indicate that the soil structure in SHMS fields can recover more quickly than conventional sites and that more water is found in the lower depths at SHMS due to greater infiltration. The results, along with continued analysis of soil, water, and pore architecture, will allow for a quantitative understanding of soil structure change in relation to rainfall.
Hydrochemical Response to Climate Change in a Tropical Glacierized Watershed, Volcán Cayambe, Ecuador
Ally Jacoby, Crystal Ng, Joel Barker
Tropical glaciers are highly vulnerable to climate change and are experiencing accelerated retreat, raising water security concerns for the populations that rely on them for freshwater. However, the hydrogeochemical impacts of glacier recession on water resources are poorly constrained. This study aims to characterize and quantify the catchment-scale hydrologic response to glacial retreat in a tropical Andean watershed, La Dormida on Volcán Cayambe, using ion and isotope tracers (collected in 2019 and 2020) and a hydrochemical mixing model. Specifically, we characterize the unique geochemical and stable water isotope signatures of meltwater, stream and groundwater samples throughout the watershed and then use these as inputs to the mixing model, which quantifies the glacial melt contribution to stream flow. La Dormida provides a critical source of irrigation water to nearby communities, and our results inform an understanding of future water supply vulnerability due to glacial retreat.
Understanding How Seasonal Sediment Flux Varies in a Northeastern Pacific Fjord
Abigail Wilwerding, Vera Pospelova
Due to the changing climate, there are large variations in sediment load and primary productivity in coastal ecosystems, including fjords. Saanich Inlet is a unique and highly productive fjord located on the southeastern tip of Vancouver Island, British Columbia. The presence of a sill restricts deep water circulation creating an anoxic bottom in the central basin. The fjord also experiences a temperate climate, is ice-free, and has nutrient inputs from local rivers and upwelling from Pacific coastal waters. Because of these features, the fjord experiences conditions conducive to phytoplankton growth and is characterized by high primary production. A total of 84 sediment trap samples were collected from 2011 to 2012. The sampling interval ranged from 3 to 15 days, averaging seven days, allowing for a high-resolution study. All samples were split, desalted, centrifuged, dried at 45°C, and weighed analytically at the Paleoenvironmental Laboratory (ESCI, UMN). The preliminary results show that fluxes were higher during the winter and spring seasons, especially in 2011. With 2011 being cooler and dryer due to the La Nina event, sediment fluxes in the inlet were higher due to enhanced local primary production.
Sensitivity of Iron and Sulfur in the Hyporheic Zone of a Riparian Wetland
Samantha Perez, Crystal Ng, Cara Santelli
Riparian hyporheic zones are locations in the streambed where deeper groundwater, which is often anoxic, mixes with surface water, which is usually oxic. The conditions where these two waters meet promote steep redox gradients. In this work, we are studying hyporheic zone dynamics at the Tims Branch wetland in South Carolina, which has experienced uranium contamination from a near by nuclear power plant. The porewater in the organic-rich sediment of the Tims Branch wetland is contains iron and sulfur, which may be important for the oxidation of carbon via redox reactions. Iron is important because it’s involved with the formation of microbial mats which can immobilize the uranium, and the sulfur is thought to mediate iron reactions in the hyporheic zone. This study uses a reactive transport model to determine how sensitive dissolved iron and sulfur concentrations are to the change in flux conditions and how much iron and sulfur are present at the sediment-water interface. The reactive transport model uses Monod kinetics to simulate the change in redox species in the vertical profile of Tims Branch. The model includes a sequence of redox reactions involving different terminal electron acceptors (TEAs). The reactive transport model shows how the concentrations of dissolved iron and sulfur differ under the different scenarios, which is vital for calibrating the model to the Tims Branch wetland.
Oxide and accessory minerals in "hybrid rocks" record subduction zone fluid-rock interactions
Natalie Raia
The subduction of tectonic plates is a primary mechanism by which Earth materials are recycled into the mantle. Over the course of subduction, water stored in tectonic plates is released with increasing depth (higher pressures and temperatures). The released fluid facilitates the formation of arc volcanoes and aids in governing the location and style of seismicity along the subduction interface. Evidence for fluxing of large volumes of fluid is present in the existence of ‘blackwall’ or ‘hybrid’ rocks, which are common in exhumed subduction complexes and form directly from fluid-rock interaction with surrounding rocks. Often dominantly comprised of hydrous phases such as amphibole (actinolite, tremolite) and phyllosilicates (talc, chlorite, biotite), we here focus on accessory phases (apatite and magnetite) in two differing hybrid rocks- a talc schist and a chlorite schist from the exhumed subduction complex on the island of New Caledonia. Electron microprobe major and trace element maps and spot analyses show both magnetite and apatite crystals record trace element zonation, which we interpret to represent changing fluid conditions over the course of formation of these rocks. We compare and contrast these results within the context of existing geochemical work and conceptual models for iron oxide-apatite (IOA) ore deposits globally. Finally, we present a preliminary exploration applying existing thermodynamic tools to test options for constraining P-T-fO2 conditions for these unusual and understudied rocks.
Rachel Tripp, Sang Lee, Peter Kang
Groundwater in the Platteville Limestone formation at the Minnesota Library Access Center (MLAC) on the UMN campus has been contaminated with petroleum products since the 1960’s. The spread of contaminants such as naphthalene and benzene poses a particular risk to groundwater resources due to their carcinogenic properties. In this study, we study the potential of in-situ bioremediation by directly visualizing bioremediation processes in laboratory experiments. Microfluidic devices have recently emerged as an innovative laboratory experimental platform as they allow direct observation of physical, chemical, and biological phenomena at the pore-scale. We recreated a subsurface environment in polydimethylsiloxane (PDMS) microfluidic chip and conducted flow experiments to investigate how pore-scale flow and biomass growth in porous media affect bioremediation. We isolated nine microbes that are capable of using naphthalene as the carbon source and compared their growth rate to select the microbe with the fastest biodegradation rate. Then, the selected microbe was injected to microfluidic chips using a high precision syringe pump to directly observe how they colonize pore spaces and analyze its implications on bioremediation using a fully motorized fluorescence microscope. The improved understanding at the pore scale may lead to efficient strategies that enhance field-scale bioremediation efficiency.
Rachel Tripp, Tingying Xu, Cara Santelli
Specific strains of ascomycete fungi have the ability to oxidize soluble Mn(II) to form insoluble Mn(III/IV) oxides. Due to biogenic Mn oxides’ high reactivity and negative surface charge, they can act as natural sponges for many heavy metal contaminants (e.g., cobalt, nickel, copper). Because Mn oxides are insoluble in near-neutral pH environments, they are easier to remove from solution along with adsorbed metals. Earlier work in the Santelli lab with Mn-oxidizing fungi used HEPES buffer, a Good’s buffer, to grow the fungi and keep the pH near neutral. We conducted experiments to determine if the oxidation remained efficient when using a bicarbonate buffer, which is a more environmentally conscious and realistic alternative to HEPES buffer. Ascomycete strain F1, isolated from the Soudan Iron Mine, was grown in a salty, metal rich solution with Mn(II) and Co(II) as the metals of interest for co-precipitation, thus removing these metals from solution. Over time, the change in aqueous Mn and Co concentrations were quantified in order to inform fungal bioremediation strategy. Through this, it was determined that samples exceeding a critical concentration of bicarbonate buffer were able to remove all Mn and Co from solution. This ongoing work will help develop fungal bioremediation strategies applicable to treating salty, metal-contaminated wastewaters such as those created by mining operations.
Emma Link, Jessica Gutknecht, Jacob Jungers, Chris Fernandez
Soil physical and chemical health are rooted in soil microbial communities that process organic material and improve soil structure. However, the relationships between commonly used soil health indicators and soil microbial community characteristics are not well studied. This knowledge gap is especially clear in novel perennial agricultural systems where extensive root systems and minimal disturbance are thought to foster robust soil microbial communities and improve soil health. Kernza is the grain of intermediate wheatgrass (Thinopyrum intermedium) being developed as a perennial grain crop by the Land Institute. In this study, we investigate the microbial communities, mycorrhizal associations, and soil chemical and physical properties of four cropping systems in their first year of growth; Kernza, Kernza with alfalfa (Medicago sativa) intercropping, no-till soy/corn (Glycine max, Zea mays) intercropped with winter wheat/hairy vetch (Triticum aestivum, Vicia villosa), and tilled soy/corn. Twenty replicates of each cropping system were grown in a single field planted in a randomized block, split plot design in Rosemount, MN. We characterize the bacterial and fungal communities present in the soil using high-throughput sequencing of the 16s and ITS regions, respectively. We also quantify root mycorrhizal associations through root staining, as well as extracellular enzyme activity. Finally, we link these metrics to common measurements of soil chemical and physical health including basic soil chemical properties, bulk density, aggregate stability, total C/N, and POX-C. Results are pending.
Titanium in deforming quartz and the thermomechanics of detachments and thrust systems
Paxton Buboltz, Donna Whitney, Christian Teyssier
Quartz is among the most abundant and ubiquitous minerals in the earth’s crust, and it is capable of deforming at a wide range of temperatures and strain rates. These traits could make it a useful tool to determine deformation history. Titanium in quartz concentrations have recently been linked to different deformation regimes found in a compressional setting, but the relationship in an extensional setting still needs further research. We will be examining the microstructures in samples from the Swiss Alps, along with several samples from the western United States that represent an extensional environment. These microstructures will then be compared with titanium concentrations found using an electron microprobe. Finding a solid relationship between titanium concentration in quartz and microstructures, and thus temperature and pressure of deformation, has huge implications for the ease at which deformation histories can be reconstructed.
A study of magnetite growth in high-pressure, low-temperature metamorphic rocks of New Caledonia
Julianna Benson, Natalie Raia
Talc and chlorite schists are hybrid rocks that form during intense fluid interaction with mafic and ultramafic rocks in subduction zones. These rocks can be used to better understand fluid flow during subduction and exhumation. Magnetite crystals form over a wide range of pressures and temperatures and can often be found in these altered rocks. In this way, magnetite may record information about multistage fluid histories experienced by these rocks. In this study, we use XCRT scanning and petrography to examine magnetite populations within a talc and a chlorite schist. In addition to CT scanning hand samples, we picked individual magnetite grains in order to determine the presence or absence of mineral inclusions across a range of grain sizes. Initial results show that in the talc schist sample, the magnetite is euhedral, forms a strong foliation, and consists of a spectrum of grain sizes ranging from 125 μm up to 1 mm in size. Additional grain separates were mounted in epoxy for future microprobe analysis to identify any chemical differences across grain size populations. Future work aims to assess the feasibility of employing novel (U-Th)/He geochronology methods.
Quantifying soil nutrients after subsurface drainage installation
Aaron Frankl, Dr. Lindsay Pease; Dr. Anna Cates
The challenges of irregular and higher intensity precipitation in the Upper Midwest due to climate change has led to the expanded use of subsurface drainage in agricultural fields. The use of subsurface drainage aerates the soil profile, altering nutrient cycling of both nitrogen and carbon. Before the 2020 growing season, four 15-acre plots (corn-soybean-wheat rotation) were established with alternating drainage patterns (two undrained and two drained) in NW Minnesota. Soil, water, and gas samples attempting to quantify nitrogen and carbon losses have been collected since Fall 2019. Initial results from several soil assays will be presented: potentially mineralizable carbon (PMC), water extractable organic carbon (WEOC) and nitrogen (WEON), and standard soil nutrient analysis. These assays illuminate the impact of drainage on soil nutrients during the first year of drainage installation. The results, along with continued analysis of soil, water, and gas samples, will allow for a robust understanding of nutrient movement in relation to subsurface drainage, providing support and research-based recommendations for growers in the Upper Midwest.
Modeling flow paths in the hyporheic zone using microfluidic devices
Izzy Keefe, Michael Chen, Peter Kang
The hyporheic zone is a key biogeochemical hotspot which influences nutrient cycling and contaminant transport due to the mixing of rapidly replenished surficial waters with highly reactive pore waters, and is an important influence on fluvial and riparian ecosystems. Recent studies of the hyporheic zone have shown that turbulence generated in a stream can migrate deep into the bed, which will have a strong impact on mixing and biogeochemical reaction. This departs from typical models of the hyporheic zone which assume that porous media flow is strictly laminar. Recent evidence also indicates that grain scale interactions play a significant role in this migration of turbulent flow. To better understand how turbulent eddies migrate through a porous media, flow and transport in the hyporheic zone are modeled on the grain scale using microfluidic devices and a fluorescent dye tracer. In this system, cylindrical pillars serve as analogues for individual grains of a porous media, while a channel represents the region of a stream near the boundary of the porous media. The pillar arrangement is varied while maintaining the same porosity to explore how overall packing arrangement affects turbulence migration. The porosity at the channel flow-porous media interface is also modified to examine the influence of the near-boundary region on turbulence migration. The results indicate that turbulent flow is capable of propagating well into the pore space, but is controlled by the packing of the pillars, particularly near the boundary of the porous media. These results have significant implications for the transport of material in the hyporheic zone.
Differential Thermal Analysis Using Standard Rock Magnetic Equipment
Rashida Doctor, Joshua Feinburg
Measurements of susceptibility as a function of temperature are an important, standard method of understanding the magnetic minerology of a sample. These measurements are used to identify Curie/Néel temperatures of constituent minerals and show evidence of thermally-induced oxidation and formation of new magnetic minerals. The High Temperature Susceptibility Bridge (KappaBridge) is a common instrument used to measure magnetic susceptibility in many paleomagnetism labs around the world. On the other hand, differential thermal analysis (DTA) is technique used to measure phase transitions and exo-/endothermic reactions by measuring deviations in temperature from a steady heating rate. Because the KappaBridge is designed to heat samples at a relatively constant rate, the standard susceptibility measurement can be used to obtain similar information, albeit crude, about the phase transitions taking place. For standard samples to goethite and maghemite, we were able to use the difference between the heating curve for the sample and that of a blank run, to identify DTA-analogous information. In the case of goethite, this phase transition did not have a corresponding expression in measured susceptibility, demonstrating that this approach expands the utility of this common piece of equipment. Using maghemite and goethite, we were able estimate the minimum energy of reactions that can be detected via this method.
Paleomagnetic Study of Boars Tusk, a Lamproitic Volcanic Neck in Southwest Wyoming
Josie Welsh, Emma Schneider, Joshua Feinberg
Boars Tusk is a heavily eroded volcanic neck located in southwest Wyoming as part of the Leucite Hills volcanic field. This 2.2 Ma volcanic feature is one of the world’s only surficial deposits of lamproite, a rare ultrapotassic, mafic rock. In 1980, Sherriff and Shive published a paleomagnetic study that included results from Boars Tusk, which in turn have been used to help create the Apparent Polar Wander Path (APWP) for North America. However, these measurements pre-date modern paleomagnetic protocols and here we provide an updated view of its paleomagnetic recording. Additionally, since this feature has a unique silicate mineral assemblage, this research sets out to carefully characterize the rock’s magnetic mineral assemblage to determine when its magnetization was acquired (e.g., at the time of initial cooling or during subsequent alteration events). Principal component analysis of alternating field demagnetization data indicate that both the lamproite and the volcanic breccia around the base of Boars Tusk record a reversed magnetic polarity generally consistent with the results of Sherriff and Shive (1980). This recording is typically carried by minerals with coercivities >50 mT and initial susceptibility measurements indicate maghemite and titanomagnetite as likely magnetic carriers. However, many samples display evidence of secondary magnetizations held by lower coercivity grains, perhaps remagnetized during lightning strikes or by thermal reheating events shortly after emplacement. Additional information about the paleomagnetic recording of these rocks will be gained from thermal demagnetization results and rock magnetic experiments, including susceptibility as a function of temperature, major hysteresis loops, and backfield curves. It is our hope that this more comprehensive view of the magnetic properties of Boars Tusk will provide a more confident interpretation of the state of the Earth’s magnetic field at the time of volcanism.
Kawe Gidaa-naanaagadawendaamin Manoomin (First we must consider Manoomin)
June Sayers, Maddy Nyblade, Hannah Jo King, Alex Waheed
Manoomin, the Ojibwe word for wild rice (Psi in Dakota, Zizania palustris in Latin), grows in shallow lakes and streams and provides physical, spiritual, and cultural sustenance as a sacred food and relative for Anishinaabe, Dakota, and other Indigenous peoples across the Great Lakes region of North America. Manoomin abundance across North America has unfortunately been declining due to multiple environmental stressors since the onset of Euro-American colonization. Yet when it comes to Manoomin stewardship, Indigenous voices have not been adequately involved in either university research or state decision-making. In 2018, an interdisciplinary group from the University of Minnesota came together with natural resource managers from tribes and inter-tribal organizations to study Manoomin within its socio-environmental context. The collaborative that formed was given the Ojibwe name: Kawe Gidaa-naanaagadawendaamin Manoomin or First, We Must Consider Manoomin. Our deepening understanding of Manoomin across cultural worldviews is beginning to guide restoration efforts for both Manoomin and its socio-ecological environment, including the restoration of tribal, state, and university relationships. In this collaboration, we are learning how tribal knowledge and Western biophysical measurements can together inform the geochemical analysis and the ecohydrologic models of culturally significant Manoomin waterbodies. Additionally, through reflections on our two-years of university-tribal collaboration and through interviews and surveys of tribal agency staff, Minnesota state officials, non-tribal Manoomin harvesters, and researchers and students on our team, we are understanding a wide diversity of perspectives and relationships with Manoomin. We will share key questions, challenges, and insights that have emerged for us about how to protect Manoomin and engage in inter-cultural, interdisciplinary research that supports long-term resource protection and tribal sovereignty.
A Tale of Two Springs: Water temperature and pH from springs within the Platteville Formation along the bluffs of the Mississippi River
Gustav DeMars, Lilly Thach, Joshua M. Feinberg
The Ordovician Platteville Formation underlies much of the Twin Cities Metropolitan area. Predicting the flow of groundwater through this unit (as well as contamination from anthropogenic activities) is challenging due to the complicated network of fractures and partings that occur within its dolomite layers (Ca,Mg(CO3)2). This challenge is particularly evident in the highly variable water chemistry of closely-spaced springs that emerge from between the Magnolia and Hidden Falls members of the Platteville Formation along the bluffs of the Mississippi River just north of the University of Minnesota Medical Center. St. Mary’s spring emits anoxic groundwater rich in dissolved ferrous iron (Fe2+), supporting a microbial community dominated by Gallionella and Leptothrix. These microorganisms oxidize Fe2+ to ferric iron (Fe3+), which is rapidly converted into minerals like goethite (FeO(OH) and hematite (Fe2O3). The deposition of these minerals below the spring streaks the bluffs with a bright orange color that becomes darker red downslope (and provides the imagery for the spring’s religious name). Additionally, calcite (CaCO3) is precipitated from dissolved calcium ions and bicarbonate as the spring’s water degasses CO2, forming small (<1 cm) rimstone dams and tufa-like deposits near West River Parkway. By contrast, a second spring only ~10m away from St. Mary’s emerges from the same stratigraphic level with very different qualities. This unnamed spring has a lower flow rate, higher dissolved oxygen, and shows no oxide or carbonate mineralization. Here we present temperature and pH data collected from both springs. We hope to learn more about the hydrogeologic settings of these springs and the interactions they capture between water, microbes, and minerals.
Strategic Placement of Green Infrastructure for Urban Stormwater Control
Xiating Chen, Xue Feng
Although effective in reducing upstream inland flooding, the high celerity in urban gray infrastructure increases flooding and sediment destabilization downstream, and it leads to a sharper peak flow in the hydrograph. With increasing concerns around stormwater qualities at outlets, engineers are weighing the trade-off between upstream drainage efficiency and downstream safety, and are re-thinking green space in stormwater controls. To understand the spatial effects of green infrastructure on flow control performance, stormwater retention networks with varying locations and densities of green infrastructure are simulated in a storm event. While in general the more green infrastructure or the higher cumulative drainage area lead to more effective flood mitigation results, the actual locations of the green infrastructure are also not trivial. In particular, my hypothesis is that the same topographical and connectivity characteristics of the green infrastructure nodes may result in different flow control outcomes given varying rainfall scenarios. At higher rainfall intensity, the implementation of green infrastructure near outlets may produce desirable flow control outcomes, but with more frequent lighter rainfalls, implementing upstream may more effectively control outlet flow rates. The simulated model will be applied to different watershed planning scenarios in the Twin Cities metropolitan area.
A micro- to macro-scale relationship study between mineral hosts and their inclusions: implications for Quartz-in-Garnet (QuiG) barometry
Alexis Stricker, Clementine Hamelin
The conventional approach to determining the depth (P) and temperature (T) experienced by metamorphic rocks (geothermobarometry) relies on thermodynamic/chemical equilibrium between minerals. An alternative approach is inclusion barometry, which focuses on the mechanical equilibrium (i.e., balance of stresses) experienced by an inclusion encapsulated by a host mineral. Once there is a change in P-T, the strain in the inclusion, inflicted by the host, can be measured and the original conditions of entrapment can be retrieved.
Garnet is an abundant mineral that typically grows throughout metamorphic rock history, and often contains many quartz inclusions, making this mineral pair ideal for ‘Quartz-in-Garnet’ (QuiG) inclusion barometry. However, previous studies on the applicability of QuiG suggest possible over- or under-estimates due to post-entrapment modification, possibly releasing pressure in the inclusion. How do host-inclusion relationships influence results of QuiG barometry?
We investigated a sample from a well-studied suite of metamorphic rocks showing systematic and moderate increase in grade from low to high P-T (Barrovian metamorphism). We extracted individual garnets from the rock and used X-ray Computed Tomography (XRCT), Electron Backscatter Diffraction (EBSD) and Electron-probe Microanalysis (EPMA) to investigate the shape and distribution, crystallographic orientation (microstructure), and microchemical variations in garnet hosts and their quartz inclusions. We find that quartz inclusions are elongate and strongly aligned within garnets, and their crystallographic orientation suggests they were entrapped during constriction as the rock was deforming. Garnet likely experienced two episodes of growth and show complex microchemical exchange with garnet. These results provide important information about the chemical and structural relationships between inclusion and host minerals and must be carefully considered when applying inclusion barometry.
Petrochronology and trace element thermobarometry reveals processes and conditions of eclogite retrogression in an exhumed (ultra)high-pressure metamorphic terrane
Hannah Blatchford, D.L. Whitney, C. Teyssier
Continental crust can be subducted to mantle depths and undergo ultrahigh-pressure (UHP) metamorphism (depths > ~100 km) before returning to the surface during collisional mountain building events. In some cases, areas of exposed (U)HP rocks are found as large (>10,000 km2) coherent terranes. The record of deformation within these largest (U)HP terranes provides valuable information for understanding how significant volumes of continental crust respond to exhumation; a fundamental process in the lifecycle of collisional orogens.
Localized (meter-scale) ductile shear zones are a common occurrence in the Western Gneiss Region of Norway, a large exhumed (U)HP terrane. The shear zones are hosted in quartz- and feldspar-rich gneisses, and contain bodies of variably retrogressed eclogite. Both rock types regularly include titanite (CaTiSiO5), a promising accessory mineral chronometer for tracking metamorphism and deformation processes through time. Eclogite bodies also contain the mineral chronometer rutile (TiO2). Quartz (SiO2) is present in all lithologies. We leverage the trace element chemistry and textures of these minerals to investigate the geochemical and metamorphic processes associated with eclogite retrogression. Microanalytical techniques (laser ablation ICP-MS and electron probe microanalysis) show that texturally distinct populations of titanite and quartz have different compositions. When combined with rutile chemical data, these differences allow for reconstruction of a portion of the WGR’s pressure-temperature history. We supplement micro-scale observations with outcrop mapping of shear zones to link geochemical trends to deformation during terrane exhumation. Together, these datasets yield a detailed record of how deformation and metamorphism interact during decompression of a coherent (U)HP terrane.
Assessing marine dissolved organic carbon response to climate change: a modeling approach
Maya Gilchrist, Katsumi Matsumoto
The ocean holds one of the largest near-surface reservoirs of carbon on Earth, with the marine dissolved organic carbon (DOC) pool roughly equaling the total amount of carbon stored in the atmosphere. Emerging evidence suggests that marine DOC is a significant component of the global carbon cycle, though little is known about how global climate perturbations have impacted the size of the DOC reservoir in the past, and consequently how this reservoir may evolve under future climate change scenarios. In order to quantify the influence of global climate change on the DOC reservoir, we propose to calibrate a dynamical earth system model to reproduce modern DOC observations in the global ocean at steady state. We will use the calibrated model to investigate changes to the size of the DOC reservoir in response to climate forcing under glacial boundary conditions.
Quantifying Soil Organic Matter After Subsurface Drainage Installation
Kyle Sherbine, Anna Cates, Lindsay Pease
Installation of subsurface drainage systems is growing in Minnesota as a management technique; however, the initial effect of drainage on soil organic matter (SOM) is poorly understood. Disrupting the balance of reservoirs that store nutrients for immediate and long-term use could rapidly lead to soil infertility. We aim to determine how two pools of soil organic matter, particulate and mineral-associated, change after drainage installation. Particulate organic matter, compared to mineral-associated organic matter, is physically larger and more readily available to microbes. We expect greater changes to particulate organic matter throughout the soil profile. This two-year study began in fall 2019 and will be conducted at the University of Minnesota Northwest Research and Outreach Center in Crookston, MN. The goal of this project is to help us evaluate the role that SOM depletion plays in nutrient cycling in recently drained soils, and whether drainage is likely to increase or decrease total C stocks. Additionally, this project will help to provide growers with research-based recommendations regarding fertilizer practices and long-term soil health management for sustainable agroecosystems.
Serpentinization of mantle in the Bogota Peninsula, New Caledonia
Lily Hershley, Natalie H. Raia
New Caledonia preserves one of the world's largest ophiolite nappes, an emplaced slice of oceanic crust and mantle on land. The Bogota Peninsula, located on the eastern coast of the island, exposes an interpreted ancient oceanic transform fault that preserves a wide zone of ductile deformation. Its high-temperature history of deformation has been studied using a variety of structural, microstructural, magnetic, and geochemical tools, but the later, cooler history of serpentinization is largely unexplored. Hydration of the Bogota Peninsula could have occurred at three different points in its history: when the peridotite cooled and fractured, as the mantle was thrust on to the island, and during ongoing surficial serpentinization. The presence of serpentine within peridotite lithologies is important because its relatively weak properties play a large role in strain localization. Identifying certain types of serpentine may tell us something about their relative chronologies and environment of formation. However, serpentine polymorphs can be hard to recognize petrographically. In this study we combine petrography and Raman microscopy to identify polymorphs of serpentine and sequence the progressive history of serpentinization of these rocks.
Integrating Cover Crops and Manure: Best Management Practices
Manuel J. Sabbagh, Melissa L. Wilson, and Paulo H. Pagliari
Cover crop (CC) adoption rates are low, particularly in the upper Midwest region of the USA. Producers are becoming more interested in integrating CC in their farm management systems, especially when manure is utilized as a nutrient source. Our aim with this study is to develop and demonstrate best management practices which could be used to integrate CC and manure in cold climates. This three-year study began in spring 2019 and is being conducted at the University of Minnesota Research and Outreach Center in Waseca, MN. Various CC species and seeding methods were evaluated and liquid dairy and swine manure were injected through sweeps to minimize soil disturbance during early and late fall. We aim to determine the effects of the combination of CC and manure have on soil health, nutrient cycling, and agronomic responses in comparison to the two practices alone.
Fabric Development Within Shear Zones: How and When?
Christine Newville, Teyssier, Christian, Whitney, Donna, Blatchford, Hannah
Shear zones are studied for their role in moving large volumes of material laterally and vertically to bring deep crustal rocks toward the surface of the Earth. This movement may occur in multiple stages, and an important aspect of characterizing and therefore understanding shear zones is detecting the record of multiple stages of deformation, particularly in networks of shear zones. However, the characterization of networks is limited by two-dimensional exposures that lack connection to other nearby deformational structures and observations. The characterization of shear zones is crucial in understanding the path through changing temperature and pressure domains, kinematics, and rate and timing of exhumation of deep rocks to shallow levels. The Roan Peninsula, in the Northern Western Gneiss Region of Norway, is a window of a metamorphic complex which records multiple stages of deformation through processes such as shearing and folding in the rock, including crenulation folding, and multiple generations of leucosomes (crystallized melt) that are either folded or form planar veins in the axial surface of crenulation folds. The region is structurally characterized as a NE-SW trending dome bounded by steeply dipping shear zones in hornblende +/- garnet gneiss with local mafic pods and layers. Three shear zones appear to have worked together in order to accommodate the exhumation of migmatites and high-pressure granulites. We examine records of deformational structures, mineral assemblages, and geochronology in an effort to understand regional shear zones and their relationship to each other and collective participation in regional deformational events. We present relationships between structural, microstructural, and petrological observations within a regional shear zone network to illustrate the history of the exhumation of deep crust in the Caledonian orogeny.
Does dental morphology reflect diet in modern and fossil squamate reptiles?
Evan Whiting, David Fox
Diet is an important component of animal ecology, and for many vertebrate animals, their teeth are directly related to their diets. Teeth readily fossilize, so they provide an ecological proxy that can be extended into the geologic past, allowing us to reconstruct the diets of extinct animals. Quantitative measures of tooth shape and complexity are commonly applied to modern and fossil mammals, but these techniques have still not been widely applied to non-mammalian vertebrates, such as squamate reptiles (lizards and snakes). Therefore, we used high-resolution computed tomography (CT) scans and three-dimensional dental topography analysis to quantify and investigate tooth morphology as it relates to diet in a sample of extant squamates (n = 69). We then applied these methods to a sample of fossil lizards (n = 8) from the Paleogene of Wyoming and North Dakota in order to reconstruct their diets. We used four dental topography metrics summarizing tooth shape and complexity and tested for the effects of size, number of teeth, and phylogeny on all of our resulting values. We found considerable overlap in dental topography values among four dietary categories (carnivores, invertivores, omnivores, herbivores), although there are still some general trends, such as greater tooth complexity in herbivores than carnivores. Phylogenetic signal is moderate to strong (Pagel’s λ > 0.60) for most of our dental topography metrics, as well as for number of teeth. Size has little to no impact on our results, although two metrics are slightly effected by number of teeth. Even when phylogeny is taken into account, some of our metrics can still reliably differentiate among dietary categories significantly (p < 0.05), demonstrating that phylogeny does not completely swamp ecomorphology in extant squamate teeth. Based on comparisons with our modern dataset, the Paleogene fossil lizards were most likely carnivores and/or invertivores, similar to some of their closest living relatives.
Gravity-driven instability in fracture flows with miscible fluids of different densities
Hongfan Cao, Seonkyoo Yoon, Zhenyu Xu, Laura Pyrak-Nolte, Etienne Bresciani, Peter K. Kang
Many important subsurface processes and applications, such as geologic carbon sequestration, enhanced geothermal system, and magma flow in dykes, involve flows of variable-density fluids in geologic fractures. Understanding the role of variable-density flow on transport, mixing, and geochemical reactions is essential for the prediction, design, and operation of the subsurface activities. In reality, vertical fractures are common, and flow and transport in vertical or inclined fractures will determine the integrity of caprocks. However, the effects of density contrasts on flow and mixing in vertical fractures have rarely been studied.
In this study, we combine visual laboratory experiments and direct three-dimensional (3D) numerical simulations to study the effects of fracture inclination angle (orientation relative to gravity), flow inertia, and density contrasts between fluids on the spatiotemporal distribution of miscible fluids in a fracture. Two miscible fluids with different densities are injected through two inlets at the bottom of the fracture and flowed out from the outlet at the top of the fracture. The density contrast between two injection fluids results in the lighter fluid being confined to a narrow path, which we term “runletâ€, and the instability of this runlet is observed in both visual lab experiments and 3D numerical simulations. We investigate the underlying mechanisms triggering the instability in variable-density fracture flows by systematically conducting numerical simulations for various combinations of flow rates, density contrasts, and fracture inclination angles. Our results show that the runlet is formed by the complex interplay between the density contrast, inertia effects, and mixing, and the runlet instability is controlled by 3D vortices.
Chloride Concentrations and Specific Conductance in TCMA Groundwater
John McDaris, Joshua M. Feinberg; Anthony C. Runkel, Jonathan Levine, Sophie Kasahara, and E. Calvin Alexander, Jr.
Here we review historical chloride concentrations in the groundwater of the Twin Cities metropolitan area (TCMA) in Minnesota as a case study to examine chloride contamination of regional aquifers, primarily from the seasonal application of salt to roadways. We have examined data from 374 wells collected between 2005 and 2017 which sample the major aquifers underlying the TMCA. Though the natural background chloride concentration in this region is <10 mg/L, 69% of measurements from these wells are above 10 mg/L (703 of 1020) and multiple aquifers already yield median chloride concentrations elevated above background levels. Of these elevated concentrations, most (87%) remain below chronic exposure limits set by state and federal authorities. However, chloride concentrations will continue to increase in these aquifers as surface waters migrate into underlying aquifers. Most of the wells included in this study are monitored annually, making it impossible to detect important sub-annual fluctuations in chloride concentrations that are known to occur in the region and that will become increasingly important for water resource managers to monitor in the future. In addition, paired measurements of chloride concentration and specific conductance were examined within this hydrogeologic context. Specific conductance is shown to be an effective means for quantitatively monitoring chloride concentrations in the uppermost aquifer of the TCMA and for qualitative monitoring of deeper units. If automated conductance sensors were strategically deployed at existing monitoring wells, they could serve as a rapid and inexpensive means for identifying where chloride concentrations are increasing most rapidly and the rate at which chloride is being transported to deeper aquifers.
Fossil vs. non-fossil CO sources in the US: New airborne constraints from ACT-America and GEM
Andres Gonzalez, Dylan B. Millet, Xueying Yu
We interpret an ensemble of airborne measurements with a high-resolution atmospheric model to place constraints on US fossil and non-fossil carbon monoxide (CO) sources. Measurements spanning the eastern half of the US reveal a low bias in the simulated CO background and a 30% (13-46%) overestimate of US fossil fuel CO emissions in the 2016 National Emissions Inventory. After correction we apply the optimized model to partition the observed CO by source. During summer, regional fossil fuel sources account for just 9-16% of the sampled boundary layer CO, and 32-38% of the enhancement due to North American sources—limitating the utility of CO as a fossil fuel tracer. The remainder predominantly reflects biogenic hydrocarbon oxidation with some fire contribution. Fossil sources likewise account for less spatial variability at this time than non-fossil and background contributions. The regional fossil contribution rises in other seasons, and represents 57-84% of sampled wintertime enhancements.
Effects of olivine symmetry and fabric type on shear wave splitting in the mantle wedge
Lindsey Kenyon, Ikuko Wada
The mantle wedge flow pattern, which is due to the drag of the subducting slab on the viscous mantle, controls the thermal structure of subduction zones and affects many subduction zone processes, such as arc volcanism, metamorphic reactions and earthquakes. In previous studies of global-scale upper mantle flow, it has been observed that the fast polarization direction of S-waves aligns with mantle flow directions. The polarization of shear waves during propagation through anisotropic media, referred to as shear-wave splitting (SWS), is attributed to the crystal preferred orientation of an elastically anisotropic mineral olivine, which developes as the mantle deforms. In models of global upper mantle flow, A-type olivine fabric is assumed, and although the crystal symmetry of olivine is orthogonal, it is commonly simplified to hexagonal symmetry, also called transverse isotropic symmetry. This simplification results in a good match between observed and calculated S-wave fast directions beneath ocean basins where the mantle flow pattern is fairly simple. However, in subduction zones, where the flow pattern can be complex, the observed S-wave fast directions are spatially more variable, even within a single subduction zone. Some studies of mantle flow in subduction zones that model SWS have assumed hexagonal olivine, while others have used specific and sometimes spatially variable olivine fabrics. In this study, we examine the impact of assumed olivine symmetry and fabric on SWS parameters, using 3-D mantle wedge flow patterns that are predicted by simple thermo-mecahnical subduction models.
Towards the Auto-detection and Classification of Small Seismic Events with Deep Learning
Zhao Zhu, Max Bezada, Kai Welsh
The volume of seismic data has increased exponentially over the last few decades, which poses great opportunities and challenges for the extraction of useful information, such as the occurrence and location of small seismic events, from the seismic time-series. The recent development of deep learning algorithms and tools has brought us plenty of possibilities to explore, given their advantage over traditional machine learning methods when the amount of data is very large. In this study, we delve into the application of Graph Neural Networks (GNN) over the detection and classification of seismic events in the region of east Wyoming and west South Dakota. The CIELO array, consisting of 24 broadband seismic stations, was deployed in that region to investigate the lithosphere's anomalous thickness associated with the topography at the Rocky Mountain Front. The region is rich in events related to mining blasts, which share impulsive first arrivals with natural earthquakes but differ in the overall shape of the source function. Since the availability of labelled data is crucial for deep learning tools, we involve citizen scientists to help us pre-process the data. From our cooperation with students without a geophysical background, we are optimistic about the quality and reliability of the analysis done by people with proper, yet simple training. Eventually, with assistance from citizen scientists, we will be able to evaluate the GNN's ability in processing structured seismic array data, and potentially analyse the clustering of seismic events with respect to the lithosphere's thickness. Our ultimate goal is to generalize the use of GNN and other deep learning tools to data from other dense seismic arrays, providing a reliable pipeline for the discovery and characterization of small seismic events.
Experimental Investigation of Mantle Heterogeneity Using Partitioning of First-Row Transition Elements Between Clinopyroxene and Melt with Varying Jadeite Components
Heidi N. Krauss and Fred A. Davis
Earth’s mantle is generally thought to be composed of peridotite, but subducted oceanic crust may be present as lithological heterogeneities in the mantle. These lithological heterogeneities may contribute to the diversity of magmas generated in the upper mantle, such as the chemical differences between ocean island basalts and mid ocean ridge basalts [1]. First-row transition elements (FRTE) have been used for identifying basalts formed from partial melting with a component of recycled crust [2,3,4]. FRTE are distributed differently between crystals and melt depending on the composition of the minerals in the melting source [4]; therefore, to accurately model FRTE concentrations in melts derived from different lithologies requires constraints on the compositional effects on partitioning of those elements. To better understand how FRTE partitioning is affected by differing mineral compositions I performed experiments focusing on the partitioning of FRTE between clinopyroxene and silicate melt as a possible indicator of mantle heterogeneities. Five parent compositions with variable Na concentrations were created and used in piston cylinder experiments. I performed experiments at a pressure of 2 GPa and temperatures between 1000-1100°C. The data presented will be SEM imaging, and electron microprobe analysis. These data sets will demonstrate how increasing Na concentrations in clinopyroxene effects the partitioning of FRTE. This will improve modeling of the compositions of melts derived from heterogeneous mantle sources in future work.
[1] Zindler & Hart 1986, Ann. Rev. Earth Planet. Sci.; [2] Humayun et al. 2004, Science; [3] Le Roux et al. 2011, Earth Planet. Sci. Lett.; [4] Davis et al. 2013, Geochim. Cosmochim. Acta.
The Role of Ester Sulfate and Organic Disulfide in Mercury Methylation in Peat Soils
Caroline Pierce, Olha S. Furman, Sarah L. Nicholas, Jill Coleman Wasik, Stephen D. Sebestyen, Randall K. Kolka, Carl P.J. Mitchell, Natalie Griffiths, Edward A. Nater, and Brandy M. Toner
Peatlands hold large quantities of atmospherically deposited mercury and can be significant sources of neurotoxic methylmercury (MeHg). MeHg is known to be a product of sulfate reducing bacteria. In this study we examined the size, composition, and spatial correlation of sulfur and mercury pools in peatland soil depth profiles. The relationships between sulfur and mercury species were assessed by measuring sulfur 1s XANES spectroscopy, total mercury and MeHg concentrations by CVAFS, and the instantaneous potential methylation constants via mercury isotopes. MeHg concentration and organic disulfide (R-S-S-R’) mol fraction were spatially correlated, with maxima located in the zone of water table fluctuation, and a significant positive correlation (p < 0.05) with depth was observed. This finding is consistent with these chemical species being products of dissimilatory sulfate reduction processes. Conversely, a significant negative correlation between organic monosulfides (R-S-H , R-S-R’, mol fraction) with MeHg concentrations was observed and is consistent with the reduction of Hg2+ bioavailability via complexation reactions between Hg2+ and organic monosulfides in peat. Finally, a significant positive correlation between ester sulfate (R-O-SO3-H, mol fraction) and instantaneous potential methylation rate constants was observed and is consistent with ester sulfate being a substrate for mercury methylation via dissimilatory sulfate reduction. Our findings point to the importance of organic sulfur species in mercury methylation processes, as substrates and products, as well as potential inhibitors of bioavailability. In addition, for a peatland system with sub-µmol / L porewater concentrations of sulfate and hydrogen sulfide, our findings indicate that the solid-phase sulfur pools, in the concentration range of 1000 - 3000 mg S / kg peat, may be accessible to microbial activity and/or exchanging with the porewaters over short timescales.
Iron Sulfide Hosted Microbial Community in the Deep Subsurface
Christopher Schuler, Cara M. Santelli, Brandy M. Toner
Communities of microbes are commonly found in isolated aquifers in the continental crust; however, much remains unknown about their structure and function. These microbes are thought to primarily reside in biofilms on mineral surfaces; however, the bulk of the research on these communities has been limited to data gained from water samples, which may not accurately describe these biofilm-hosted microbes. To better understand mineral-hosted microbes in the subsurface, we characterized sediment samples extracted from boreholes in the Soudan Underground Mine State Park. Located in northeastern Minnesota, the Soudan Mine accesses a 2.7 Ga banded iron formation. Boreholes located on the lowest levels of the mine, 714 m below the surface, extend over 100 m into the crust and are known to access an aquifer containing a microbial community. Sediment samples were collected from this aquifer and preserved under anoxic conditions. They were first characterized through X-ray diffraction (XRD) to determine the identity of their crystalline mineral phases. Next, the Scanning Transmission X-ray Microscope (STXM) at the Advanced Light Source was used to image the particles and to characterize the iron and carbon phases in the sample. The XRD pattern identified the particles as mackinawite, an iron sulfide. STXM data confirmed the presence of iron in the sample and showed that several organic carbon phases were associated with it. Gaussian fitting of X-ray absorption spectra extracted from the STXM data will be used to identify the iron and carbon phases present. This data will shed more light on microbe-mineral associations in the subsurface and give insight into how biofilm-hosted microbes might differ from their better-studied planktonic counterparts.
Unlocking deformation history by linking quartz geochemistry and microstructure
Jennifer Taylor, Christian Teyssier, Donna Whitney
Quartz is an important mineral for facilitating deformation in the Earth’s crust. However, the history of deformation preserved in quartz chemistry and microstructure is often erased or modified by progressive deformation. This study leverages combined geochemical and microstructural analyses of ductilely deformed quartzite in order to extract a multi-stage history of deformation and exhumation from the Wildhorse detachment shear zone, a bounding structure of the Pioneer metamorphic core complex, Idaho. Quartzite samples from the shear zone contain three distinct microstructures: matrix quartz that has been recrystallized by subgrain rotation, highly elongate quartz ribbons, and relic quartz grains representative of the material prior to subgrain rotation recrystallization. Semi-quantitative maps of Ti concentration in quartz were constructed from cathodoluminescence images and quantitative Ti spot analyses. Ti concentrations in quartz are sensitive to both pressure and temperature and can record the conditions of deformation. Patterns of Ti concentration were linked to quartz microstructure by combining these data with detailed EBSD analyses. Quartz ribbons and relic grains are characterized by high Ti concentrations indicative of high temperatures (600 – 750 °C) whereas recrystallized matrix quartz is characterized by low Ti concentrations indicative of lower temperatures (350 – 500 °C) during recrystallization. These correlations between Ti concentration and microstructure suggest that 1) recrystallization is required to reset Ti concentrations during deformation and 2) quartz crystals that do not undergo recrystallization can maintain a record of conditions early in the history of an exhuming shear zone. Combining microstructural and geochemical data not only provides insight into how ductile deformation influences Ti equilibration in quartz but also provides a means to reconstruct a large portion of the deformation history from a single rock sample.
Evaluating 21st-century extreme heat risks in Minnesota urban areas
Jonathan Birkel, Tracy Twine, Stefan Liess, Laurence Kalkstein
Extreme heat is often overlooked as a public health concern in Minnesota, where intraseasonal summer variability limits acclimatization to oppressive heat conditions. Specific categories of synoptic-scale air masses are particularly linked to summer excess mortality. In the past 75 summers, Minnesota urban areas have experienced narrowing diurnal ranges and decreased nighttime cooling, while hot and humid air masses have increased in frequency at the expense of cooler and drier ones. This study utilizes downscaled climate projections for mid and late 21st-century Minnesota, including moderate and high emissions scenarios, derived from eight general circulation models. Outputs from downscaled gridcells representing urban areas, whose populations are most susceptible to heat-related mortality, are used to generate daily spatial synoptic classifications. The study aims to identify frequency and character trends in the highest-risk air masses in order to establish a basis for estimating, and potentially mitigating, future heat-related health outcomes.
More than fun in the sun: The pedagogy of field trips supports student learning in higher education
Jabari Jones, Susan Washko
Field experiences are a fundamental and well-loved tool for teaching in the eartch sciences. However, a number of concerns threaten continued incorporation of field experiences into courses, including increased class sizes, strained finances, liability, accessibility concerns, and the effects of COVID-19. Because of these barriers, it is critically important to investigate and articulate the value of field trips to better advocate for their continued implementation. By reviewing existing literature on traditional field trips and courses, virtual field experiences, and accessible field trips, we have identified several attributes that contribute to the value of field trips as a pedagogical tool.
The strength of field activities lies in 1) the integration of active learning, 2) the co-creation of knowledge through collaborative, problem-based activities, 3) place-based learning that provides real-world context, and 4) rapid feedback between peers and instructors. These strategies are well-represented in scholarship on teaching and learning, and further, strategies implemented in field learning may help to reduce the achievement gap for underrepresented groups. Applying the four attributes of field trip pedagogy to classroom and virtual classroom activities, as well as to virtual field trips, can improve teaching and learning when field trips are not possible. Instructors should aim to re-create as many of these attributes as possible to design courses that are as impactful as those involving traditional field trips.
From Rapid Response to Sustained Action: 2020-2021 Diversity, Equity, and Inclusivity Initiatives in the Department of Soil, Water, and Climate
Persephone Ma, Jennifer Nicklay
Following the murder of George Floyd in May 2020, some members of our department community experienced a reckoning with the overt and systemic racism in the United States. The Department of Soil, Water, and Climate (SWAC) undertook a two-part initiative to assist people interested in personal journeys of anti-racism and to develop and gather ideas for systemic changes at the department level. This initiative led to the development of SWAC’s Diversity, Equity, and Inclusivity (DEI) Roadmap, a department-level implementation plan for acknowledging and undoing systemic racism. Building on the Roadmap, in the 2020-2021 academic year, a seven-person DEI committee has been actively continuing DEI work within the department. Additionally, SWAC is participating in the National Science Foundation’s (NSF) national initiative Unlearning Racism in the Geosciences (URGE), which seeks to equip people with theoretical frameworks regarding anti-racism, guide people in taking explicit anti-racist action through policy deliverables, and share these deliverables across departments and institutions to usher in a change across the field as a whole. In this talk, we will discuss the process that SWAC took to develop our Roadmap and reflect on its effects on the department since then. Our goal in this presentation is to share the tools and frameworks we’ve developed with other faculty, students, and departments to inspire their own work. We also seek to continue building cross- departmental and institutional relationships, with the understanding that building just systems will require our collective action.
Magnetostratigraphy of the Eocene Green River Formation, Wyoming
Emma Schneider, Joshua M. Feinberg, Riley Lamers, Josie Welsh, M. Elliot Smith, Alan R. Carroll
The Green River Formation (GRF) is one of the most well-preserved continuous Eocene terrestrial records in the world, allowing researchers to track phenomena in high resolution related to climate, tectonics, and geomorphology. The preservation of the early Eocene is of particular interest as it spans the Early Eocene Climatic Optimum (EECO), an analog for current greenhouse gas-driven global warming. Geochronologic constraints in the section are under development, limiting the temporal resolution of ongoing research. Magnetostratigraphy of the GRF is challenging due to the pervasive growth of authigenic pyrrhotite in sediments (Sheriff and Shive, 1982). In this study, we build on the work of Tsukui and Clyde (2012) by collecting paleomagnetic data from ash-fall tuffs, which are more resistant to authigenic sulfide growth and can be dated directly using U/Pb and 40Ar/39Ar geochronology. Geomagnetic polarity was determined using alternating-field and thermal demagnetization protocols and we can now infer the position of the five geomagnetic reversals encompassed by chrons 23R and 23N. The samples’ magnetic mineral carriers are magnetite, hematite, and their titanium-substituted equivalents and were characterized using hysteresis loops, backfield curves, and magnetic susceptibility. Fe-sulfides are present in some samples, and repeated susceptibility measurements show that secondary magnetic minerals form during thermal demagnetization steps >450°C, but most samples generally show minimal post-depositional alteration and still retain reliable paleomagnetic information. The timing of the geomagnetic reversals will further refine the geochronology of the GRF, providing a framework for ongoing research into Eocene cyclostratigraphy and enabling correlation with the marine record.
Assessing the functional diversity of mammalian communities from Hall’s Cave, Texas, over the past 15 kyr
Nora Loughlin, David Fox
The Pleistocene-Holocene transition is of great interest to paleoecologists, as this interval experienced several rapid warming and cooling events, as well as a size-biased extinction event that killed off the majority of North American megafauna. While many studies have analyzed the taxonomic diversity of North American mammalian communities since Last Glacial Maximum, comparatively few have assessed their functional diversity. Functional diversity is a metric of ecosystem function, and communities with high functional diversity may be more resistant to ecological disturbances. As such, a functional approach to studying mammalian diversity provides a more nuanced understanding of these communities. The fossil record of Hall’s Cave provides a unique lens through which to examine functional diversity through time. This central-Texas site has been extensively excavated in 5 cm intervals, and radiocarbon dating has shown that sediments excavated from Hall’s Cave were deposited over the past approximately 15 kyr. We used 3 categorical functional variables (size based on log body mass in grams, diet, and locomotor mode) to assess several aspects of functional diversity: functional richness (how many functional niches are filled within a community), functional evenness (how regularly species are distributed in functional space), functional divergence (how symmetrically species are distributed to partition functional space), and functional dispersion (how widely the species are distributed in functional space). We find that total species richness is at its maximum during the Younger Dryas Stadial, and at its minimum during the Holocene climatic optimum; however, the number of functionally unique species remains roughly the same during this time interval. Functional richness and divergence do not change during this interval, and functional evenness gradually increases. These results suggest decreasing functional redundancy in the communities from more recent sediments.
Exotic earthworm invasion alters soil temperature profile in Minnesota deciduous and coniferous forests
Sara DeLaurentis, Kyungsoo Yoo, Holly Francart
In temperate deciduous and coniferous forest ecosystems, it has been observed that the feeding and burrowing activity of certain exotic earthworm species are capable of dramatically altering the structure of the forest floor. When these species are present, they mix and may even altogether remove the layers of fresh and decomposed organic material that would typically cover the mineral soil. Removal of some or all of the organic layers has a major impact on the thermal properties of the soil surface, and upon the soil temperature profile. In order to determine the impact of earthworm activity on different forest floor types, temperature sensors were installed at sites in deciduous and coniferous forests, at both high and low earthworm invasion intensity. Sites were located near Itasca State Park, and selected based on criteria indicating severity of earthworm invasion. Sensors were installed at multiple depths: at the top of the soil profile, the start of the mineral surface (immediately below surface sensor if the organic layer is 0cm thick), 10, 30 and 50cm below the start of the mineral horizon. Temperatures were recorded from November 2019 to July 2020. Our data shows that when the organic layers are intact, in both forest types, they provide a significant insulating effect for the mineral soil below.
Harsh Anurag, Crystal Ng, Kathy Tokos, Robert Tipping
Vegetation changes occur in response to climate variability as well as due to human-imposed land-use change. These changes affect water moving past the root zone and recharging groundwater. We investigate the sensitivity of groundwater recharge in Minnesota to temporally dynamic vegetation across varying climate and ecoregions. We use a physically based, distributed model, Community Land Model (CLM) and adopt a probabilistic approach using Ensemble Kalman Filter (EnKF) to condition uncertain model parameters and outputs on groundwater level observations. Preliminary results show notable difference in simulated recharge between climatological and transient vegetation, demonstrating the sensitivity of recharge to vegetation dynamics.
Hannah Blatchford
The metamorphic and deformation history of continental crust subducted to and returned (exhumed) from mantle depths to the mid-crust is best accessed in ultrahigh-pressure (UHP) metamorphic terranes. The largest UHP terranes, including Norway’s Western Gneiss Region (WGR), are thought to be exhumed as coherent blocks with minimal internal deformation. Within the WGR, there are numerous high strain zones with textures indicative of deformation over a range of pressures during exhumation. This suggests that the high strain zones record a potentially extensive segment of the exhumation path, which I investigate here using U-Pb titanite ages and chemistries.
Paul Burley
Distribution and orientation of Neolithic earthen long barrows and the Dorset Cursus are summarized with regard to geomorphologic conditions on chalk downlands of Cranborne Chase in central southern England. Long barrow directions reflect the orientation population of valleys and interfluvial ridges , focusing attention toward the English Channel and the horizon between the Isle of Wight and Isle of Purbeck headlands. Viewed from highest elevations of the Chalke Escarpment, the Dorset Cursus demarcates the southeast horizon between the Isle of Wight and the Isle of Purbeck. Locations and orientations of the monuments unify the architecture with natural physiography of the Chase.
Aubrey Dunshee, Gene-Hua Crystal Ng, Douglas Kent, Brandy Toner
Groundwater arsenic (As) contamination is a global health concern. However, many studies on As-contaminated groundwaters focus on warmer climate settings with little temperature variability. Due to this bias, temperature-dependent As mechanisms have not been adequately explored. This study uses a reactive transport model to evaluate the effect of seasonal temperature changes on As fate and transport in lake-shadow porewaters downgradient of three lakes on Cape Cod, MA that span a gradient of nutrient and organic levels. Preliminary findings show that sensitivity of As release to temperature variability depends on degree of eutrophication, where highly elevated levels of organic matter override the effects of temperature in mobilizing.
Samuel Fleagle, Natalie Raia
The study of subduction zone fluids is important for understanding the role fluids play in subduction zones, metamorphic rock formation, and how temperature and pressure effect the role fluids play in ongoing subduction. Veins formed during high-pressure, low-temperature (HP/LT) metamorphism are critical to our understanding of the chemistry of subduction zone fluids. HP/LT rocks from lawsonite to eclogite-facies metamorphism on New Caledonia contain garnet and epidote veins formed through mineralization from metamorphic fluids. Using X-ray computed tomography, electron microprobe analysis, and petrographic analysis we characterize the morphology and chemistry of these veins, studying how they vary with temperature and pressure.
Xin Jin, Yu-Xiu Zhang, Donna Whitney, Xiao-Yao Zhou, Jun-Cheng Hu, Shahbaz Bin Khalid
The comparison between weakly retrogressed jadeitite and strongly retrogressive elogite (S-Ec) demonstrate that rutile in weakly retrogressed jadeitite records the prograde and peak metamorphic conditions. Nb is a very sensitive trace element in decoding the different metamorphic stages in the fresh jadeitite but not the strongly retrogressed eclogite owing to retrograde re-equilibrium of trace elements. The much higher contents of Ep in S-Ec indicate higher water content, which promoted retrogression. The peak metamorphic fluid is significantly more enriched in Nb, likely originating from mineral decomposition (e.g. amphibole) during prograde metamorphism.
Morgan Johnstone, Gene-Hua Ng, Leah Nelson
The Ecuadorian Andes support climatically unique systems, most notably, tropical, mountainous glacierized watersheds that supply water to many local communities. These regions are particularly susceptible to climate change effects. We aim to evaluate the changing contribution of glacial meltwater to both surface and ground water, as well as preferential flow paths through the watershed over changing temperatures. To accomplish this, we pursue a geochemical understanding of the region through bulk composition X-Ray Diffraction and granular microprobe analyses, coupled with principal component statistical analyses of water chemistry data. Results from these analyses and the implications on the meltwater contribution are presented here.
Jabari Jones, Andy Wickert
Humans have dramatically altered the landscape of the Upper Midwest, changing the way that water and sediment are routed through stream networks. Ongoing climate change exacerbates these changes through more intense precipitation and changes in seasonal climate patterns. I investigated the hydrologic and geomorphic impact of land-use and climate change on the Cannon River in Minnesota using historical climate data, streamflow data, and air photos. Streamflows and river width dramatically increased over the 20th Century and have further increased in the last two decades, concurrent with the expansion of soybean farming in the watershed. Further research is needed to discern the role of climate vs. land-use change in driving these trends.
Lindsey Kenyon, Ikuko Wada
Previous studies show that a subducting slab converging obliquely to the margin drives a complex 3-D mantle wedge flow pattern [e.g., Kneller and van Keken, 2008; Wada et al., 2015], but its effects on the development of crystallographic preferred orientation (CPO) of olivine and seismic anisotropy have not been quantified. In this study, we use generic kinematic-dynamic models of subduction with varying obliquity to systematically examine the effect of obliquity on mantle wedge flow patterns and apply the crystallographic code D-Rex to the calculated flow patterns to predict olivine CPO in the mantle wedge.
Megan Korchinski, Christian Teyssier, Patrice F. Rey, Donna L. Whitney, Luke Mondy
Rift basin formation and deep crustal flow are dynamically competing processes that strongly influence the localization of deformation during extension of continental lithosphere. Both processes involve vertical mass transport that can accommodate space created during rifting, thereby affecting the strength profile of the lithosphere and extension localization. We investigate the dynamic interaction between infilling of rift basins and flow of ductile crust via a suite of 2D numerical experiments under lithospheric extension where crustal thickness, deep crust viscosity, and rift infill density are systematically varied. Our results illustrate that the deep crust viscosity exerts a first-order control on the accommodation of extension.
Brayden Kuester, Mary Sabuda, Jackie Mejia, Cara Santelli
Selenium (Se) is an “essential toxin”— it is required by most organisms for growth, but at high concentrations, Se can become toxic. Elevated environmental Se concentrations are caused by waste produced by a variety of anthropogenic activities such as mining, agricultural, petrochemical, and industrial manufacturing operations. This research will determine how various nutrients (C, N, P) and their concentrations affect the reduction of mobile Se species such as selenate (Se(VI)) by metal-tolerant Paraconiothyrium sporulosum under oxic conditions. This research can help enhance Se bioremediation strategies and improve water and soil health of environments impacted by Se.
Riley Lamers, Courtney Sprain, Joshua Feinberg
High quality measurements of the strength of the Earth’s ancient magnetic field, or paleointensity, are essential for improving our understanding of the evolution of the geodynamo; however, it is difficult to find materials whose magnetic minerals are dominated by stable single domain grains. This study examines a new candidate material for paleointensity studies: clinkers, which are rocks that have been metamorphosed by coal seam fires. We assess the magnetic mineralogy through two profiles from the Powder River Basin, Montana using rock magnetic measurements, XRD, and electron microprobe analyses. Results show that clinkers contain a high concentration of the rare mineral luogufengite, which is ideal for thermal paleointensity protocols.
Benjamin Longchamp, Josh Feinberg, Dana Smith, Laurel Goodwin, Jack Hoehn, Brian Jicha, Brad Singer
Low-angle normal faults (LANFs) have been mapped in metamorphic core complexes (MCCs) throughout the North American Cordillera, but dip too shallowly for seismic slip according to Andersonian fault mechanics. Debate over the origin of these structures is split between support for models where normal faults initiate at favorable dips and subsequently rotate to low-angle orientations (e.g. rolling hinge model) and belief that field relationships show that LANFs were active at or near their present orientation. Using paleomagnetic data from pseudotachylyte veins we show conclusively for the first time that LANFs in the South Mountains MCC in Arizona failed at low angles, producing earthquakes large enough to generate pseudotachylyte (~ M5.5).
Nora Loughlin, Anna K. Behrensmeyer, Catherine Badgley
Locality Y311 is one of the richest fossil localities within the thick sequence of Siwalik sediments spanning ~16 million years. Collections of over 4700 specimens by the Harvard - Geological Survey of Pakistan team record a diverse assemblage of mammals, birds, reptiles, and fish buried in a complex fluvial channel-fill system. Unusual pockets of fossils suggest accumulations by mammalian carnivores or crocodilians. Fossils from the GM excavation and the associated surface collected fossils were analyzed to compare the taphonomic differences of excavated and surface collected material, and to evaluate carnivore impact in the Y311 locality.
Fernando Medina Ferrer, Jake V. Bailey
Field observations are valuable to interpret ecological environments and their influence on sedimentary deposition. Here, we designed a rapid, easy and cost-effective field test to simultaneously determine the activity of microbial urease and carbonic anhydrase. Both enzymes induce carbonate precipitation and may explain potential mechanisms for the formation and dissolution of certain environmental carbonate deposits.
Kirsten Meltesen, Evan Whiting, David L. Fox
While patterns of species richness are strongly correlated to latitude, it has been shown that variation in species richness and ecological structure in North American mammals can also be explained by several climatic and topographic variables. However, as rodents make up a large proportion of North American mammals, it begs the question: to what degree does rodent variation drive trends in species richness and ecological structure observed for all mammals? The results of ongoing statistical analyses of biogeographic data will be used to compare the degree to which variation in species richness and ecological structure is explained by climatic variables for mammals as a whole versus mammals minus rodents and for rodents alone.
Morgan Monz, Peter Hudleston
Crystallographic preferred orientation (CPO), associated with mechanical anisotropy, develops as ice deforms by plastic flow. This reflects the conditions and mechanisms of deformation and influences the strength of ice. Current work on coarse-grained ice has been limited due to techniques that are restricted by grain-size and difficulty of measuring a-axes by traditional methods. We developed a new sample preparation technique that allows us to use EBSD to obtain a representative, bulk CPO on coarse-grained samples collected from Storglaciären, a sub-polar glacier in Sweden. Initial EBSD data suggests a grain-sampling bias in thin sections may result in the multiple maxima fabric that has been previously characterized in glacial ice.
Leah Nelson, Gene-Hua Crystal Ng, Leila Saberi, Morgan Johnstone
Climate change will impact water systems world wide, resulting in water insecurities among vulnerable communities. Of particular concern is the impacts of retreating glaciers in tropical regions, where glaciers traditionally provide water during dry seasons and are vulnerable to climate change. A better understanding of tropical glacierized watersheds is needed. Dissolved ions and stable isotopes of water can be used to parse out water sources, including glacier melt and groundwater. Geochemical characterization of bedrock and soil is needed to understand where these dissolved ions originate, so that they can be used to also identify flow pathways. We present preliminary analyses of mineral and water chemistry on Volcán Chimborazo, Ecuador.
Tyler Nigon, David Mulla, Ce Yang, Daniel Kaiser
Effectively managing nitrogen (N) fertilizer inputs to corn using a comprehensive ecosystem services-based approach requires that both the benefits and societal costs resulting from N application be considered. Efforts have been made to quantify the social costs of N that aim to reduce exposure to reactive N and improve general well-being. However, many of these results are based on regional or global models, and largely ignore the reality that grain yield response to N varies spatially within a field and from year to year. Results from a traditional economic response analysis will be compared to an analysis that considers an added social cost that represents unintended costs from pollution caused by reactive nitrogen.
Patrick O'Hara, Gene-Hua Crystal Ng, Josh Torgeson
Wild rice in NE Minnesota is threatened by the presence of porewater sulfide. Aqueous sulfate, which can reduce to sulfide in anoxic conditions, is released by taconite mining operations in the region. Elevated sulfate concentrations (~300 mg/L) have been measured within Twin Lakes, a former wild rice lake system that is hydrologically connected to Minntac’s tailings basin. A 2D vertical transect of the wetland connecting an external Minntac tailings basin monitoring well to Twin Lakes is being constructed. Using a combination of MODFLOW (flow model) and PHT3D (reactive transport model), the geochemical and transport history of measured sulfate and sulfide concentrations are in the process of being determined.
Hayley Orlowski, David Birlenbach, David Fox
The Inhibitory Cascade is a developmental model for mammals that predicts that tooth size is constrained by the tooth anterior to it. Many modern mammals conform to this pattern, but horses do not. To address this discrepancy, we compiled a dataset of lengths and widths of fossil horse teeth and examined the ratio of molar occlusal areas. Here we track the adherence of horses to the Inhibitory Cascade throughout the Cenozoic. Preliminary findings indicate that the earliest horses express a phenotype predicted by the model, in which molars increase in size moving posteriorly. Later equids show a shift from the ancestral phenotype towards the reverse trend, as well as showing the unpredicted phenotype of modern horses.
Natasha Peterson, Elisabeth Steel, Chris Paola
Modeling deltaic stratigraphy requires knowledge of geometric and temporal evolution of distributary networks on the delta surfaces. Overheard imagery paired with high resolution topographic scans can be used to extract channel depth, width, and water color-intensity of channels. However, aerial imagery is more readily available than topographic data in natural and experimental systems, meaning channel depth is the most difficult to constrain. Using overheard imagery and topographic scans to create data profiles of channel depths, with minimal topographic information available. The depth profiles can be utilized to best constrain channel depth for images that do not have associated topographic scans.
Sunny Qin, Renata Wentzcovitch, Michel Marcondes, Gaurav Shukla
Ab initio investigation of the Fe and Si isotope fractionation among Fe-bearing bridgmanite, metallic iron and FeSi alloy at core-mantle segregation conditions (40-60 GPa, ~ 3500 K) revealed the bridgmanite enriches heavier Fe and Si isotopes. This indicates that the core formation can explain the heavier Fe isotope signature of the bulk silicate Earth. However, the calculated Si fractionation factor between silicate and metal phase is much smaller than previous experimental measurements. Consequently, if the bulk Earth is assumed to be chondritic, the core should have ~25 wt% Si, this is contradicting to many other geophysical observations. Thus, the Earth might be non-chondritic from the perspective of Si isotope.
Leila Saberi, G.-H. Crystal Ng, Jeff La Frenierre, Leah Nelson, Andrew D. Wickert, Wei Zhi, Li Li
With global climate change, some of the highest rates of warming are occurring in tropical glacierized mountainous watersheds. This is leading to the rapid retreat of glaciers, which is already causing decreases in streamflow in parts of the Andes. Hydrochemical tracers can be used for hydrograph separation because of distinct signatures in different streamflow sources to identify the pathways meltwater takes, but typical mixing models used for this fail to spatiotemporally resolve water movement within the watershed. To address these shortcomings, we implement the integrated reactive-transport watershed model RT-Flux-PIHM for a tropical glacierized watershed on Volcán Chimborazo, Ecuador.
Mary Sabuda, Carla Rosenfeld, Todd DeJournett, Karl Wuolo-Journey, Katie Schroeder, Cara Santelli
Selenium (Se) is essential in moderate doses to most organisms for the production of selenoproteins, but elevated levels in the environment can cause detrimental and severe biological repercussions. The oxidized forms, Se(+IV/VI), are more mobile and bioavailable than elemental Se(0) or volatile Se(-II). As such, strategies reducing Se to Se(0) or Se(-II) may reduce mobility. Bench-scale culture experiments of two Se-reducing fungal isolates were performed to quantify the amount of Se removed from solution in municipal and industrial wastewaters containing elevated Se concentrations. The geochemical results from this novel work will be presented. This experiment highlights the high potential for the mycoremediation of Se in wastewater.
Gerard Salter, Chris Paola, Vaughan Voller, Marco Redolfi
Bifurcations partition the flow of water and sediment between the branches of deltas and multi-thread rivers. Previous work on the morphodynamics of fluvial bifurcations has focused largely on bifurcations where the two downstream branches have equal angles with respect to the main branch. We begin by compiling measurements of bifurcation relative angles and widths using remote-sensed imagery, and find that low-angle branches tend to be wider, suggesting that relative angle plays a role in setting discharge partitioning. To test this concept, we run a series of numerical simulations with varying relative angles and freely evolving bed morphology. We find that relative angle acts as an imperfection parameter favoring the low-angle branch.
Riley Schmitter, Josh Torgeson, Crystal Ng, Patrick O'Hara, Alex Waheed, Cara Santelli
Sulfur released from mine tailings into Minnesota waterways can inhibit growth of wild rice, a sacred plant for Native tribes in Minnesota and Wisconsin. Sulfide produced by microbial sulfate reduction complexes with iron to form insoluble FeS minerals that precipitate on plant roots, limiting oxygen and nutrient uptake. Coupled sulfur and iron cycles reduce and dissolve Fe(III) oxyhydroxides, which can release sorbed phosphate, further inhibiting rice growth. Here we analyze the distribution of phosphate in porewaters and the concentration and speciation of iron in sediments. X-ray diffraction and sediment Fe data will determine spatiotemporal changes of FeS minerals. This data will help to clarify sulfur cycles in wild rice environments.
Katie Schroeder, Jacqueline Mejia, Mary Sabuda, Brayden Kuester, Cara Santelli
Selenium (Se) is an essential element for normal cell function but can be toxic at elevated levels. Oxidized forms of Se, Se(+IV,VI) are more mobile than reduced forms, Se(0,-II), making oxidized Se more threatening to surrounding ecosystems. Certain fungal isolates can reduce Se to its less mobile forms and thus have bioremediation potential, but the mechanisms of this reduction process are unknown. We present results from batch laboratory experiments determining the amount and rate of Se(VI) reduction during growth of Alternaria alternata in minimal nutrient media with varied carbon, nitrogen, phosphorus, and vitamin sources. These experiments serve as a precursor for later genome-enabled approaches to understand Se reduction mechanisms.
Noah Slade, Amy Myrbo, Kelly MacGregor
Climate change associated with the Pleistocene-Holocene transition in the eastern Rockies is poorly understood. Here we use lake sediment cores from northeastern Glacier National Park, Montana, to characterize changes in climate and periglacial environment from 13,500 to 8000 years bp. We reconstruct the advance and retreat of Grinnell Glacier using sediments deposited by glaciofluvial processes in a chain of paternoster lakes. Using a combination of grain size, L*a*b* color space, and smear slide analyses, we identified cm-scale laminations whereby carbonate sediment eroded by the glacier was succeeded repeated by siliciclastic sediment eroded by the valley’s stream, indicating the glacial advance and retreat of the Younger Dryas.
Tatsuro Tanioka, Katsumi Matsumoto
Dissolved oxygen in the ocean has been decreasing over the past decades. Here, we use two independent methods to give a new global estimate of how much oxygen is consumed per unit of organic carbon during aerobic respiration (“respiratory quotient”). Spatial variability in respiratory quotient could be explained by the relative abundance of protein, carbohydrate, and lipid that constitute organic matter. We expect that respiratory quotient will decrease under a future warming scenario, as the composition of organic matter changes. We suggest that this shift could significantly ameliorate future deoxygenation.
Jennifer Taylor, Christian Teyssier, Donna Whitney, Rory McFadden, Alex Senjem
Quartz-hosted rutile needles have the potential to record strain in mylonitic shear zones. Microstructural analysis suggests rutile needles behave as material lines independent of surrounding quartz, recording strain through their alignment and 3D orientation. Needle orientations were measured in quartzite samples from the mylonitic Wildhorse Detachment, the bounding structure of the Pioneer Metamorphic Core Complex. Combined with EBSD analyses of the host quartz and microstructural observations, these measurements illuminate differences in strain throughout the thickness of the shear zone, suggesting a complex history of extension-related shear, possibly related to strain partitioning or overprinting within the shear zone.
Maximillian Van Wyk de Vries, Eliza Calder, Pablo Tierz-Lopez
In one of the worst volcanic disasters of the 21st century, a pyroclastic flow from Volcan de Fuego (VDF) left more than 400 dead or missing on the 3rd of June 2018. At the same time the number of Guatemalan migrants apprehended at the US border in 2018 reached over 40000, more than 50 times the number ten years earlier. Here we link both the volcanic disaster and migration crisis to a concurrent 7 year drought. Reduced streamflow and erosion enabled extreme volumes of volcaniclastic sediment to accumulate at the summit of VDF, which ultimately sourced the deadly 2018 pyroclastic flow. Multiannual crop failures and food insecurity was the reason cited by 95% of Guatemalan migrants for their departure, with many migrating north to the US.
Evan Whiting, David Fox
The Paleocene-Eocene thermal maximum (PETM) is one of the closest geologic analogs to the Anthropocene. Massive, rapid carbon release ~56 Ma caused global surface temperatures to increase by 5–8°C for ~200,000 years. Fossils from the Bighorn Basin of Wyoming document dramatic changes in terrestrial floras and faunas across the PETM. We are using computed microtomography (μCT) and dental topography methods to investigate the dental complexity of fossil lizards from the Bighorn Basin during the PETM, reconstructing their likely diets using a comparative dataset of extant lizards with known diets. This ongoing work may elucidate how lizards responded to environmental changes across the PETM, with potential implications for the Anthropocene.
Zhao Zhu, Max Bezada
Joint consideration of the seismic velocity structure and the seismic anisotropy pattern as determined from shear wave splitting in the Nevada Basin has led to the hypothesis of a lithospheric downwelling or “drip” in the region. However, although the inferred anisotropy field plays a prominent role in the interpretation, the velocity structure has been derived through isotropic tomography. In this study, we reassess the seismic velocity structure by incorporating hypothetical anisotropy fields consistent with shear wave splitting observations and the proposed downwelling into the analysis.
an be used to help predict climate change impacts.
David Birlenbach, Jonathan S. Keller, David L. Fox
Body mass is closely tied to numerous aspects of an animal’s ecology and thus is useful for paleontological inferences. Mammalian body mass is traditionally estimated using the occlusal area of molars. The relative sizes of mammalian teeth are explained by a developmental model called the Inhibitory Cascade (IC). One of the predictions put forth by this model is that the lower second molar (m2) will occupy roughly one third of the molar triplet (i.e. first, second, and third molar). Using 151 species of rodents we confirmed this prediction and tested which lower molar performed best as a predictor of body mass. The m2 was the best predictor of body mass, likely due to its relatively consistent size as predicted by the IC model.
Hannah Blatchford, Donna L. Whitney, Christian Teyssier, Stacia M. Gordon, Dina Hauge
Norway’s Western Gneiss Region (WGR) is an exceptionally well-exposed ultrahigh-pressure terrane formed during continental subduction and exhumation. The P-T-t-d exhumation history from mantle to mid-crustal depths is discontinuously preserved across much of the WGR, but numerous meters-scale shear zones are promising features for recovering a more complete record. We present results of detailed lithologic and structural mapping of four such shear zones, and use results to highlight differences in exhumation-related processes such as the extent of melting and eclogite retrogression across the WGR. Our maps provide necessary outcrop context for microstructural analyses and accessory phase petrochronology used to reconstruct the P-T-t-d path.
Kerry Callaghan, Andy Wickert, Ying Fan, Gonzalo Miguez-Macho, Jerry Mitrovica, Jacky Austermann, Crystal Ng
Groundwater accounts for 1.69% of the globe’s water storage – nearly as much as is stored in ice caps and glaciers. The volume of water stored in the ground has changed over glacial-interglacial cycles along with temporally evolving climate, sea level, ice extent, surface topography and soil properties. Using a model incorporating these, we present our estimates of changes in global groundwater storage over the past 21000 years. Estimates of depth to water table at 500-year intervals allow a comparative assessment of changing groundwater storage volumes through time. Here, I compare results using different climate model inputs, and discuss strategies for selecting the best inputs to find true past groundwater levels.
Christie Cino, William Seyfried
Yellowstone Lake is a dynamic environment that is home to more than 250 hydrothermal vents. The location of these vents provides unique chemistry that is characteristic of fluids deeper in the Yellowstone hydrothermal system. In August 2016 and 2017, hydrothermal fluids were collected from deep vents in Yellowstone Lake in collaboration with the Hydrothermal Dynamics of Yellowstone Lake (HD-YLAKE) project using novel techniques and instrumentation. Geochemical analysis results indicate these fluids are rich in volatiles, but dilute in all other chemistry, indicating it is a vapor-dominated system.
Aubrey Dunshee, G.-H. C. Ng, B.M. Toner
High arsenic concentrations have been detected in groundwater downgradient of a hypereutrophic lake in Cape Cod, Massachusetts. We hypothesize that arsenic plumes are associated with warm lake water entering the aquifer during the summer, increasing organic carbon degradation. A reactive-transport model was implemented to test this concept. Model simulations show arsenic plumes developing in the summer, when organic carbon degradation consumed oxygen, lowered pH, and caused hydrous ferric oxide dissolution and arsenic desorption from bulk sediments. In winter, organic carbon degradation decreased, and hydrous ferric oxide precipitated to immobilize arsenic. These results shed light on the role of temperature in controlling arsenic release.
Kathryn Hobart, Dan Jones, Josh Feinberg
Pyrrhotite, Fe1-xS, is the second most abundant iron sulfide mineral in the Earth’s crust and a potential contributor to acid mine drainage and other water quality concerns. The impact of sulfur-oxidizing microorganisms on its dissolution rate at near-neutral pH is poorly understood. Batch experiments conducted at pH 4.5-7 with a variety of sulfur-oxidizing environmental bacteria show an increase in pyrrhotite dissolution, as measured by sulfate release, compared to abiotic controls.
Colleen Hoffman, Sarah L. Nicholas, Daniel C. Ohnemus, Jessica N. Fitzsimmons, Robert M. Sherrell, Christopher R. German, Maija I. Heller, Jong-Mi Lee, Phoebe J. Lam, and Brandy M. Toner
In the surface ocean, iron is a growth limiting nutrient for microscopic marine life, which impacts their ability to remove carbon from the atmosphere and surface waters. While there are several sources of iron in the ocean, underwater volcanoes are the most disputed. Current studies are investigating if iron from these underwater volcanoes can be transported over long distances, and if microscopic marine life will be able to utilize the iron once it reaches the surface water. My dissertation aims to understand the chemical and physical mechanisms by which iron is transported away from these underwater volcanoes.
Patricia Kang, Donna L. Whitney, Laure Martin
This study will investigate the metasomatic history of subduction fluids, using in situ oxygen isotope and trace element analyses on lawsonite-bearing high pressure-low temperature (HP-LT) metabasalts. Samples were collected from several HP-LT belts, each of which has different geological characteristics in its occurrence (e.g., encased within mélange or within coherent metamorphic units). Direct comparisons between the results will allow us to track any significant differences in the geological processes and the geochemical consequences induced by fluid migration from the slab during the transformation from blueschist to eclogite and subsequently to the overlying mantle.
Lindsey Kenyon, Samantha E. Hansen, Jordan H. Graw, Yongcheol Park and Andrew Nyblade
The Transantarctic Mountains (TAMs), located in Antarctica, are the largest non-compressional mountain range in the world. Little is known about their origin since they are ice-covered and geologic data is limited. To investigate the subsurface structure of the TAMs, data from a 15-station seismic array, the Transantarctic Mountains Northern Network (TAMNNET), and from 4 stations operated by the Korean Polar Research Institute (KOPRI) are being employed. In this study, S-wave receiver functions (SRFs) and Rayleigh wave phase velocities are used to analyze both the TAMNNET and KOPRI data to estimate crustal thickness beneath the study area.
Ethan Kurak, Andrew Wickert, Fiona Clubb
Since the Last Glacial Maximum, ice-sheet-induced fluctuations in water & sediment supply to the Upper Mississippi River have caused it & its tributaries to aggrade & incise, leaving behind a suite of 1 to 7 terraces expressed in tributaries throughout the length of the Upper Mississippi. We mapped the terraces from LiDAR data of the Zumbro River using the automated “LSD TopoTools” terrace extraction algorithm, and extracted the terrace elevations compared to the modern channel. We fit long profiles to the terrace surfaces, comparing those long profiles to the channel long profile to identify any similarities or discrepancies. Through analysis of our data, we see how change sin river conditions are preserved in tributaries.
Jack Lange, Crystal Ng, Amanda Yourd, Chad Sandell, Andy Wickert
Second Creek is wild rice stream located on the Iron Range in northeast Minnesota. In order to understand how mining-derived sulfate affects biogeochemical cycling at Second Creek we employed inverse modeling of temperature profiles to quantify surface water-ground water exchange at the site . Unlike many sites where this technique has been applied, Second creek is a riparian wetland where low hyporheic flux is expected. Streambed temperature profiles were measured continuously over the summer of 2016 at three locations across the site. Results showed spatial variability in both hydraulic properties and hyporheic flux. Across the site, flux was upward toward the surface water for nearly the entire summer.
Luke LeBeau, David Birlenbach, and David Fox
In the pursuit of quantitative relationships between avian pedal morphology and substrate preference, principal component analyses of ungual curvature outlines and phalangeal proportions were evaluated in their facility to discriminate a phylogenetically and ecologically diverse sample of modern avian taxa into locomotor categories along the terrestrial to arboreal spectrum. Preliminary results identify proximal phalange proportion as one effective metric for separation between terrestrial and arboreal substrate use. Application of these methods to the fossil record will assign substrate preference to key specimens in the dinosaur-bird transition sequence in order to tease out trends of early arboreality within fossil birds.
Hwaju Lee, Max Bezada
Teleseismic P-wave tomography models often show low-velocity anomalies behind subducted slab. A recent study suggested that mantle anisotropy can cause low-velocity anomalies in tomographic models when isotropy is assumed. Seismic anisotropy (i.e. lattice preferred orientation, LPO) is a useful parameter to investigate mantle dynamics of subduction. It is indeed well evidenced by SKS splitting results around Alboran slab in the westernmost Mediterranean. We include anisotropy as an a priori constraint to explore such sub-slab anomaly and influence of subduction on mantle in the region.
Shane Loeffler, Amy Myrbo
Geospatial queries are a common way for geoscientists to access data from community curated domain repositories (CCDRs), yet conventions for accessing these data vary significantly between CCDRs. Flyover Country requests data from several different CCDRs, and through our work integrating these disparate data sources, we have created a body of recommendations for both CCDR and application developers for formatting the requests and returns from these valuable databases. These recommendations will improve data interoperability in the geosciences for all users of CCDRs, leading to benefits ranging from increased public data access to improved capacity to address interdisciplinary research questions.
Shane Loeffler, David Birlenbach, Amy Myrbo
Combining resources across community-curated domain repositories increases their value. We developed code, and a user interface utilizing the R package “Shiny,” for linking data points that share common identifiers between the Paleobiology Database and Wikipedia. This software identifies which taxa within a clade have existing Wikipedia articles and which do not. The underlying code could also be used to identify whether Wikipedia articles exist for a number of other geoscience queries, such as minerals within a group, formations within a supergroup, or physiographic regions within a dataset. This software highlights information common between geoscience databases and identifies gaps that could be addressed by an expert in the field.
Fernando Medina, Cécile Bidaud, Jake Bailey
The occurrence of lipid biomarkers in ancient sediments is mostly attributed to microorganisms, with no evidence that macro-organisms significantly contribute to the preserved biomarker pool. Here, we show that abundant fish fossils from the Green River Formation may have contributed to localized accumulations of the biomarker squalane in sedimentary organic matter. Visualization of biomarkers in the surrounding sediments of fossilized fish tissues using antibodies that bind to squalane suggests a link between these macrofossils and squalane in Green River Formation rocks. This scenario represents a case where abundant squalene-rich macro-organisms may have significantly contributed to squalane found in the Green River sedimentary basin.
Morgan Monz, Peter Hudleston
Storglaciären, a valley glacier in northern Sweden, was chosen to study the rheologic properties of natural ice through microstructural analysis, and to establish the relationship of the microfabric to macroscale structures. Recrystallized grains vary in both size and shape, and have weak or no shape-preferred orientation, reflecting recrystallization involving highly mobile grain boundaries. Locally, there is an inverse correlation between bubble concentration and grain size and boundary smoothness. Crystallographic preferred orientations display multimaxima patterns centered around the pole to foliation. Angular distances between maxima suggest a possible twin relationship that may have developed from a preexisting single-maximum fabric.
Patrick O'Hara, Crystal Ng, Cara Santelli, Josh Torgeson
Wetland systems are the largest natural source of atmospheric methane. Second Creek, a riparian wetland in northeast Minnesota, experiences elevated sulfate concentrations due to adjacent taconite mining activities. Recent studies have detected notable anaerobic oxidation of methane (AOM) rates in terrestrial wetland systems that are comparable to that of marine subsurface systems. AOM within marine subsurface systems is often coupled with microbially mediated sulfate reduction, but little is known about this interaction in terrestrial systems. Through analysis of hydraulic flux, microbiology, and geochemistry of the sediments of Second Creek, we are evaluating the relationship between AOM and microbially mediated sulfate reduction.
Natalie Raia, Donna L. Whitney, Christian Teyssier
Globally, arc magmas are observed to be oxidized compared to typical mid-ocean ridge basalt (e.g., Kelley & Cottrell, 2009). The contribution of subducted slab dehydration fluids to this signature is debated. Studies have primarily analyzed arc rocks and glasses, and consequently, several oxybarometers exist for igneous systems (e.g., Li & Lee, 2004). Little work exists on the oxidation state of exhumed subduction complexes, and it is unclear if existing igneous oxybarometers produce meaningful information for these lithologies. To test the potential application of these systematics to subducted rocks, we synthesize geochemical data for altered oceanic crust and present a new global compilation of eclogite major and trace element data.
Joe Rippke, Ikuko Wada
The Cascadia subduction zone is classified as a low-stress subduction zone because the magnitude of the compressive force due to plate convergence is similar to that of the gravitational force based on previous mechanical modelling results. This stress environment provides an opportunity to probe the background stresses in the subduction zone that may be masked in high-convergence-stress subduction zones. We compile and analyze focal mechanism solutions of earthquakes within the continental forearc along the length of the Cascadia subduction zone to determine the stress orientations in the forearc and their regional-scale variation and investigate their implications for subduction zone processes, such as earthquakes and fluid migration.
Elizabeth Roepke, Kelly Duhn, Grace Larson, Carla Rosenfeld, Cara Santelli
Manganese (Mn)-oxidizing microbes (4 fungi, 30 bacteria) were isolated from the Soudan Mine in Northern MN and grown in the lab under high salt, low nutrient conditions similar to water in the mine. Isolates were identified and assigned taxonomy based on DNA sequences and phylogenetic relationships. These Mn-oxidizing microbes are of interest for potential bioremediation of metals in groundwater due to their metal scavenging abilities. Biogenic Mn oxide minerals have a high sorption capacity for metal cations (Cu, Co, Ni, Zn), but this capacity may be diminished with high salt cation concentrations (Ca, Na, K). Results of microbial identification, biogenic Mn oxidation experiments, and metal sorption to biogenic Mn oxides will be presented.
Leila Saberi, G.-H. Crystal Ng, Andrew D. Wickert, Rachel T. McLaughlin, Jeff La Frenierre , Li Li
The rapid retreat of glaciers is an unavoidable consequence of climate change that alters the hydrologic cycle in glacierized watersheds. Recent surveys have also revealed rapid upslope migration of montane vegetation with warming, which will also modify the water budget through increased evapotranspiration. To investigate the combined influence of melt-water and upslope vegetation shift on groundwater recharge and stream discharge in a glacierized watershed on Volcán Chimborazo in Ecuador, we implement the Flux-PIHM watershed model. Preliminary model results are analyzed to evaluate distinct spatiotemporal characteristics of surficial and groundwater pathways of meltwater.
Mary Sabuda, Carla Rosenfeld, Cara Santelli
Selenium (Se) is both a micronutrient (required for most life) and an element of environmental concern due to its elevated toxicity in high concentrations. Some environmentally-relevant fungi can transform this essential toxin to a bioavailable form when needed (e.g., for production of the amino acid, selenocysteine) and to a solid phase when concentrations are high. Culture experiments of Alternaria alternata were created to assess the amount of biomass-associated Se and constrain the redox chemistry of this process over time. The geochemical and microscopy results from this novel work will be presented. This study will aid in identifying fungal Se transformation mechanisms and ultimately help design an efficient Se remediation strategy.
Meng Sun, Max Bezada
Intermediate-depth seismicity outside active subduction zones is rare. However, there is a well-known occurrence of such events in a N-S elongated volume between Spain and Morocco, within what most researchers consider to be the relic Alboran slab. Partial subduction of, and tearing from the adjoining continental lithosphere have been suggested in this area. We investigate whether dehydration embrittlement or shear instability is more consistent with the Alboran intermediate depth seismicity by considering their location relative to the expected thermal structure and expected areas of high strain rate associated with thinning or tearing of the slab.
Tatsuro Tanioka, Jacob Zahn, Katsumi Matsumoto
Here we present the third version of Minnesota Earth System Model for Ocean biogeochemistry (MESMO3). The new version has a prognostic nitrogen cycle and a more realistic representation of organic matter. The overall goal of this model is to advance our understanding of the global carbon cycle under late Pleistocene ice age climate.
Josh Torgeson, Cara Santelli, Crystal Ng, Carla Rosenfeld, Patrick O'hara, Kelly Duhn, Amanda Yourd, Liz Roepke, Mary Sabuda
The dynamic redox gradients in riparian wetland hyporheic zones impact biogeochemical cycles of iron (Fe), sulfur (S), and carbon. In northern MN, S emanating from mine-waste can alter expected cycles, resulting in “hidden” cycles. To gain insight into the influence of these “hidden” cycles, characterization of Fe mineral phases using X-ray absorption spectroscopy has been coupled to measurements of acid volatile sulfides, microbial data, and hydrologic data. These measurements allow for trends of Fe and S mineralogy, S (bio)availability, and the microbial influence to be elucidated. These trends will be incorporated into reactive transport models, allowing for predictions of the system’s response to biogeochemical and hydrologic changes.
Evan Whiting, David L. Fox
There are over 6,000 living species of lizards on Earth. As ectotherms, lizards generally prefer warmer temperatures, and are highly tuned to their environments. Anthropogenic climate change threatens to erode lizard diversity worldwide, especially in thermally homogeneous regions. To determine how lizard diversity relates to environmental gradients in North America, we gathered species ranges for over 200 extant lizard species, as well as a set of high resolution climatic and physiographic variables. We then conducted an ecological biogeography analysis, similar to previous studies on mammals, using a suite of multivariate statistical techniques. Our results help establish a baseline that can be used to help predict climate change impacts.