Poster Abstracts
Title: Field-Scale Evaluation of Wind Erosion, Soil Health, and Sugar Beet Productivity under Cover Crop Rye in Minnesota
Authors: Mehmet Ozturk, Anna Cates, Lindsay Pease
Keywords: Wind Erosion, Cover Crop, Soil Health, Sugarbeet Yield and Quality
Abstract: Although the sugar beet industry contributes significantly to Minnesota's economy, intensive use of heavy machinery leads to soil degradation. This study evaluated the effects of cover crops on wind erosion, sugar beet yield, and soil health through station and on-farm trials (2022-2024). The station experiment, located in Crookston, MN, included four treatments (interseeded mustard and rye, control, and fall-planted rye) with six replications on 7 m x 12 m plots. On-farm trials were conducted at Polk and Renville counties with differing weather and erosion conditions. Each site was divided into rye and control treatments. Monthly sediments were collected using nine BSNE samplers per treatment, and soil samples were taken from 0-20 cm depth before subsequent crop planting. Results indicated that interseeded cover crops did not affect sugar beet yield or quality in the station experiment. However, winter rye had more pronounced effects on soil health in the on-farm trials, as shown by Principal Component Analysis, which revealed no significant treatment differences in the station experiment. Soil and weather conditions played a larger role across both experimental sites. Rye effectively mitigated horizontal mass flux when well-established, and temperature increases correlated with higher erosion rates. Over 80% of total sediment flux occurred under no cover crop, with approximately 75% of sediment flux occurring at heights of 0-15 cm, suggesting that rye is particularly effective in preventing wind erosion when it covers the soil surface.
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Title: Geochemical and textural analyses of the lawsonite to epidote transition
Authors: Sara E. Hanel, Donna L. Whitney, Jennifer T. Mitchell
Keywords: Lawsonite, Epidote, Subduction
Abstract: Lawsonite (Lws) is a major host for H2O (~11.5 wt%), transition metals (Fe, Ti, Cr), and trace elements (Sr, Pb, U, Th, REE), and is therefore a significant mineral in element cycling during subduction (Spandler et al. 2003; Fornash et al. 2019). The breakdown of Lws is a fundamental process in the mobilization of H2O and elements from slab to mantle wedge to volcanic arcs. If slab temperatures exceed the stability of Lws during subduction and/or exhumation, reaction products include epidote-group minerals (EGMs). EGMs share similar characteristics with Lws, such as hosting Sr, Pb, and REE, and H2O (~2 wt%) (e.g. Spandler et al. 2003; Enami et al. 2004). Despite the importance of this transition for the chemical and thermal evolution of subduction zones, there is an incomplete understanding of how the Lws-EGM transition influences element budgets. The replacement of Lws by EGMs and other minerals commonly results in tabular pseudomorphs that typically do not contain relict Lws. However, EGMs that develop in former Lws-bearing rocks may contain Lws inclusions and/or “Lws ghosts” inferred from tabular-shaped epidote domains that have a different composition from the host epidote (Figure 1). The occurrence of partially-reacted Lws in some of these features indicates that tabular domains lacking Lws were former Lws. We present geochemical analyses of metabasalts from New Caledonia and Türkiye (Elekdağ) recording the disappearance of Lws and appearance of EGM, with a focus on compositional and textural characteristics of EGM containing lawsonite inclusions and “ghosts”.
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Title: Understanding the influence of fracture network characteristics and fluid density on solute transport in sedimentary fractured rocks
Authors: Porraket Dechdacho, Matthew R. Sweeney, Jeffrey D. Hyman , and Peter K. Kang
Keywords: Flow and transport in fractured media
Abstract: Complex interactions between geological heterogeneity and fluid properties govern flow and transport in fractured media, impacting applications such as contaminant remediation, geothermal systems, and carbon sequestration. Although previous studies have examined the effects of fracture network properties and density-driven flow, we still lack fundamental knowledge about the effects of sedimentary rock features, such as vertical fractures and bedding plane fractures on solute transport.
In this study, we developed field-inspired three-dimensional discrete fracture networks (3D DFN) using dfnWorks to systematically investigate how fracture network properties affect solute transport under variable-density flow conditions. We examined two structural characteristics: fracture intensity (P32 = 0.01, 0.05, and 0.5) and the presence of BPP, as well as hydrogeological properties, particularly the ratio of vertical to horizontal fracture permeability, under conditions with and without density contrast. Solute breakthrough curves and mass partitioning between fractures and the matrix were analyzed to evaluate transport behavior. Results indicate that BPP strongly influences transport in low and medium P32 networks, inducing preferential flow and multi-modal breakthrough curves. Low fracture connectivity in these networks leads to unique flow paths and reduced mass recovery. However, a high permeability contrast between vertical fractures and BPP can mitigate these effects, promoting a more uniform BPP-dominated flow. In high-P32 networks, enhanced fracture connectivity diminishes BPP influence, creating more uniform flow resembling homogeneous media and increasing mass recovery. However, reducing vertical fracture permeability enhances BPP influence and increases flow path heterogeneity. Across all cases, effects of density-driven flow were not significant due to dominant fracture flow. These findings highlight the importance of structural and hydrogeological properties in fractured sedimentary aquifers, where preferential pathways as well as network permeability and connectivity primarily control transport over density effects.
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Title: Controls on Surface and Groundwater Levels and Their Relation to Water Quality in Wild Rice Lakes in the Otter Tail River Watershed, MN
Authors: Shauna Capron, Gene-Hua (Crystal) Ng, Cara Santelli, Amelia Olsen, Madeline Dickenscheidt, Zhaashiigid Nooding
Keywords: Wild Rice, Surface water-groundwater interactions, Contaminant Transport, Water Quality, Agricultural Pollutants
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Title: Comparing Ring Width and Binary Surface Intensity Proxies for Thuja occidentalis Dendroclimatology
Authors: Naomi Schulberg, Daniel Griffin, Kurt Kipfmueller, Andrew Wickert
Keywords: Dendrochronology, climate, cedar, tree-ring, midwest, proxies
Abstract: We conducted a study to assess the potential of Thuja occidentalis (northern white cedar) to establish annual long-term records of climate in Minnesota and the nearby region, where climate change is manifesting with rising temperatures and elevated risks for both flooding and drought. However, observational meteorological records in this region are spatially and temporally sparse, as is the published tree-ring data network, limiting our ability to contextualize recent climatic changes. T. occidentalis presents a promising opportunity to study seasonal paleoclimate in the region, often living to be over 500 years old, with subfossil wood found to be even older. We developed chronologies of earlywood, latewood, and total ring widths and evaluated tree growth synchrony and relationships with temperature, precipitation, and drought. The strongest tree ring–climate relationship occurred between total ring width and May–July drought, and trees growing along lakes exhibited stronger responses to climate than those at bog sites. We also studied Binary Surface Intensity (BSI) as a novel proxy to capture climate signals beyond ring width measurements. We created a procedure for extracting BSI data and examined the different climate signals reflected in BSI, and ring width measurements. Preliminary results indicate that BSI shows different climate signals than ring width, and may reflect temperatures at the end of the summer, as well as drought in some areas. We will continue to develop these chronologies to fill spatial gaps in the regional tree-ring data network while implementing new reproducible and transferable methods in tree-ring data development.
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Title: Use of Eliptical Fourier Analysis to Discriminate Osteoderm Placement In Alligatoroidea (Crocodylomorpha) With Description of Novel Osteoderm Morphologies
Authors: Hayley K. Orlowski, Alex K. Hastings
Keywords: Caiman, Morphometrics, Osteoderms, Morphology
Abstract: Osteoderms (ossifications within the dermal tissue) are a common component of many vertebrate skeletons and can be found in all living species of crocodilian, as well as many fossil species. Under certain taphonomic regimes, soft tissue decay and transport may lead to disarticulation of osteoderms or even complete dissociation from endoskeletal remains, complicating study of morphology in fossil taxa. Despite fossil crocodylomorph osteoderms being common at numerous fossil sites, their proper placement within the body has received little analytical study. We report on the skeletonisation and archival of a nearly complete (>95%) dermal skeleton of a Cuvier’s Dwarf Caiman (Paleosuchus trigonatus), with anatomical observations and new terminology for the positional identification of individual osteoderms. Individual osteoderms were digitally photographed and their outlines extracted, allowing for morphometric examination using two-dimensional elliptical Fourier analysis (EFA). As the dermal shield of Paleosuchus has an unusually high osteoderm count (>800 individual elements) and extends across much more of its body than is typical for crocodilians, we have only attempted to apply EFA to dorsal osteoderms. Following Fourier decomposition, osteoderms were analyzed using linear discriminant analysis (LDA) to examine whether EFA constitutes a valid method of identifying anatomical position of isolated osteoderms. Counter to our expectations, results show poor discrimination of osteoderm placement on both snout-tail and left-right axes, suggesting EFA does not constitute a useful means of determining osteoderm placement in fossil crocodilians. We additionally report observations of multiple novel osteoderm morphologies in the Smooth-Fronted Caiman, wherein individual osteoderms are apparently composed of multiple fused ossifications; this morphology has never to our knowledge been observed in any organism, living or extinct.
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Title: Characterization of Lawsonite in Eclogite from the Central Pontides, Türkiye
Authors: Charles W. Petty, Donna L. Whitney, Jennifer T. Mitchell
Keywords: lawsonite, eclogite, blueschist, metamorphic petrology, garnet, omphacite
Abstract: Lawsonite is a key mineral in the process of element cycling and fluid transport in subduction zones. While it can travel deep into subduction zones, lawsonite often doesn't return to the surface intact. One such location with intact lawsonite is the Elekdağ area in the Central Pontides, Türkiye. This location is a part of the Central Pontide Supercomplex, which largely contains middle Jurassic to middle Cretaceous belts of metaserpentinite and metabasalts(Okay, 2013). Through petrographic analysis, key minerals such as lawsonite, garnet, omphacite, phengite, glaucophane, and epidote have been described. A particular eclogite sample contains lawsonite in its matrix alongside omphacite and garnet, which isn't seen in any other Elekdağ eclogite samples so far. Electron-probe microanalysis(EPMA) was then used to map garnet grains in the lawsonite eclogite for changes in major elements. Alongside the petrography, these data are useful for learning more about the metamorphic histories of high-pressure, low-temperature metabasalts.
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Title: Titanium-in-quartz applied to complex microstructures within a contact metamorphic gradient
Authors: Lydia Tuttle, Christian Teyssier, Donna L. Whitney
Keywords: Quartz, deformation, recrystallization, annealing, temperature, pressure, microstructure, diffusion, titanium, metamorphic, pluton, quartzite, Montana
Abstract: Quartz is a widely studied mineral both in the laboratory and in nature because it controls the rheology of the Earth’s continental crust and is stable at a wide range of temperatures and pressures. The rheology of quartz is affected by factors such as temperature (T), pressure (P), and presence of fluids or other phases. This study aims to evaluate quartz deformation as T changes. A suite of deformed quartzite was selected for this purpose; samples were collected within the dynamic contact metamorphic aureole of the McCartney Mountain Pluton, SW Montana, at increasing distance from the contact with the granodiorite that was emplaced at ~3 km depth at the likely temperature of ~700°C.
Elements such as titanium (Ti) and aluminum (Al) can substitute for silicon in SiO₂, quartz. These elements may diffuse through quartz grains during annealing (T increased) or dynamic, deformation-induced, recrystallization. With Ti-in-quartz thermobarometry, the concentration of Ti in quartz [Ti] is related to temperature and pressure. This study combines Ti-in-quartz quantitative spot analyses using an electron microprobe, cathodoluminescence (CL) imaging that highlights the presence of Ti and Al, and electron backscatter diffraction (EBSD) that maps the crystallographic orientation of quartz grains. The quantitative [Ti] measurements are used to calibrate the CL maps, which are themselves overlaid on the EBSD maps. Results produce semiquantitative [Ti] maps that help understand the record of T preserved in different microstructures. These microstructures include normal zoning, patchy zoning, and oscillatory zoning of Ti in quartz, as well as healed micro-cracks. This suggests that several stages of the rocks’ thermal, fluid, and deformation-recrystallization histories were recorded on the thin section scale. This study shows that quartz deformed and recrystallized in a contact metamorphic aureole preserves progressive stages of the thermal, fluid, and deformation history. This complex grain-scale record is likely related to the rapid heating and cooling within the metamorphic aureole of a shallow pluton such as the McCartney Mountain pluton, and therefore to the short time available for diffusional processes.
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Title: Local versus Regional Patterns of Growth in Red Pine in North-Central Minnesota
Authors: Kjersten Peterson, Kurt Kipfmueller, Sean Dunham
Keywords: dendrochronology, fire, climate, Upper Great Lakes
Abstract: The forests of the Upper Great Lakes region have undergone substantial changes in their overall structure and composition since intensive colonization began in the region. Certain colonial land use patterns that focused on fire suppression rather than fire-aided forest stewardship have altered forest dynamics and vegetation patterns throughout the region. Without fire to open up the canopy, to reduce competition from later-sucessional species, and to aid in the creation of an acidic, mineral seedbed, red pine struggles to regenerate. Disentangling past and present local and regional influences on tree-ring growth is useful for understanding disturbance histories, stand dynamics, and climatic influences. We developed a network of eight Pinus resinosa (red pine) chronologies from trees from Gaa-zagaskwaajimekaag (Leech Lake Band of Ojibwe Reservation) and the Chippewa National Forest. Five of the chronologies have an associated tree-ring-based fire history. These chronologies and fire histories provided us with a unique opportunity to compare the common regional growth signal among the chronologies while also examining the influence of local disturbances. We used correlation analysis to examine spatiotemporal similarity among the chronologies, and we used principal components analysis and response function analysis to examine differences in growth-climate-fire responses between the chronologies. Linking anthropogenic influences, patterns of human movement, historic fire frequency, past climatic conditions, and differences in local and regional tree-ring growth patterns can help us better understand the history of the complex socio-ecological systems of the Upper Great Lakes region.
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Title: Petrology of the Syke Rock garnet amphibolite, Franciscan Complex (Mendocino County, CA)
Authors: Sarah Brandt, Donna L. Whitney, Jennifer Mitchell
Keywords: Syke Rock, Garnet Amphibolite, Lawsonite, Franciscan Complex
Abstract: Syke Rock is a large (31 x 21 meters) high-grade garnet amphibolite block within serpentinite in the Franciscan Complex in Mendocino County near Laytonville, California (Fig. 1a, b). The petrology of Syke Rock is largely unstudied, but a Mössbaur spectroscopy study determined that lawsonite in Syke Rock contains ferrous iron, in contrast to most other lawsonite localities that are assumed to contain only ferric iron. This provides motivation for studying the petrology and geochemistry of Syke Rock.
Syke Rock’s mineral assemblage is similar to other garnet amphibolites in the Franciscan Complex: garnet ± Na-Ca to Na amphibole ± epidote-clinozoisite ± zoisite ± lawsonite ± phengite ± quartz ± rutile ± titanite ± ilmenite ± chlorite. In Syke Rock, glaucophane and lawsonite are texturally late. Coarse-grained zoisite occurs in veins that are fringed by lawsonite that has replaced garnet, (Fig. 1c). Lawsonite ± chlorite replacing garnet is also a common texture in the matrix of the Syke garnet amphibolite.
Element maps of the garnets of Syke Rock show strong zoning, with inclusion-rich, manganese-rich cores that decrease to the rim (Fig. 1d, e). The garnet rims have oscillatory zoning (concentric rings) and are inclusion-poor. Lawsonite sharply cuts across garnet zoning. Ongoing work involves reconstructing the reaction history, mineral compositions, and the P-T evolution of Syke Rock, particularly the transition from peak garnet amphibolite to lawsonite-glaucophane assemblages and the role of external fluids in forming the zoisite ± lawsonite ± chlorite veins.
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Title: Investigating stable isotopes of oxygen in firn cores from the Greenland Ice Sheet
Authors: Gabby Giving, Joel Barker
Keywords: Crawford Point, firn, 18O, climate reconstruction
Abstract: Isotope analysis is a multidisciplinary tool that allows us to better understand past and present environments by quantifying the relative abundance of stable isotopes in natural materials. The ratio of the stable isotopes of oxygen is routinely measured in ice core studies to identify changes in climate over time. Due to kinetic isotopic fractionation, the ratio of 18O to 16O in glacier ice is indicative of regional climate at the time of deposition. More negative δ18O values in ice core samples are associated with cooler temperatures while less negative values are associated with warmer temperatures. The assumption underlying this interpretation is that there has been no post depositional kinetic alteration to the distribution of stable isotope signatures. This study assesses the validity of this assumption using a firn core collected at Crawford Point, west-central Greenland. The Crawford Point core shows evidence of post depositional melting and refreezing as intermittent ice layers throughout its depth, allowing us to evaluate the effect of melting and refreezing on the interpretation of the oxygen isotope record. Understanding potential bias within the isotope record can better refine our interpretation of stable oxygen isotope proxies, and improve the accuracy of temperature reconstructions and other techniques that rely on ice core data.
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Title: Water Quality and Environmental Health in the Otter Tail Watershed: Assessing Risks for Manoomin/Wild Rice Decline
Authors: Madeline Dickenscheidt, Amelia Olsen, Shauna Capron, Zhaashiigid Nooding, Gene-Hua Crystal Ng, Cara Santelli
Keywords: Geochemical Contamination, Groundwater, Surface Water
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Title: Nitrogen Fertilizer and Cover Crop Systems in Minnesota Corn - Agronomic and Environmental Considerations
Authors: Jake Kastenbauer, Fabian Fernandez, Vasudha Sharma, Rodney Venterea, Jared Spackman
Keywords: Nitrogen dispersion, Cover crop, Nitrogen fertilizer
Abstract: As the demand for corn production increases so does the demand for nitrogen (N) based fertilizers to supplement corn growth. While ideally all fertilizer N is utilized by corn, much can be lost to the environment as nitrate (NO3), nitrous oxide (N2O), or ammonia (NH3). To enhance agronomic systems and mitigate environmental N dispersion, best management practices can be utilized. Here, urea was applied to continuous corn at 250 kg N/ha or a 0 kg N/ha control, and with select cover crop schemes (no cover, winter rye, kura clover) to assess best management practices that may result in optimal fertilizer N utilization. Rye and no cover crop treatments showed significantly great yield compared to both fertilized and unfertilized kura clover treatments, suggesting kura clover competes with corn for N availability. Volatilization of NH3 was even across rate and cover crop treatments, though these losses only accounted for a small fraction of total N applied. Greater NO3 leaching was shown with increased N rates for no cover crop and rye treatments, though this was not the case for kura clover, likely due to the continuous deposition of nitrogenous plant material from kura biomass. Greater N2O emissions were observed with increased fertilizer rates across all cover crop treatments, with the greatest emissions coming from kura clover likely due to strong microbial interactions and plant tissue deposition. Future analysis of isotopic N dispersion may help elucidate how much fertilizer derived N is accounted for in agronomic and environmental fractions.
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Title: Enhancing Soil Health Properties through Management: A Comparative Study of Soil Properties from Different Practices On a Conventional to Perennial Spectrum
Authors: Sarah E Wilson, Mckenna Kelso, Anna Cates
Keywords: Soil Health, Management Spectrum, Sustainable Agriculture
Abstract: Soil health has become an increasingly prominent topic within the soil science community, particularly in light of decades of degradation caused by intensive farming practices. While much research has focused on identifying management practices that promote soil health, questions remain regarding the most effective approaches for reversing topsoil degradation and enhancing soil resilience to disturbances. To address these questions, we conducted a study sampling soil from 31 fields across two counties within the Driftless Region of Minnesota and Wisconsin. This region, characterized by heavy topography and deep river valleys, was not glaciated during the last glacial period, resulting in fragile soils that are particularly susceptible to erosion and degradation. The management practices examined in this study range from conventional annual crop production, to systems incorporating soil health practices, such as reduced tillage and cover crops, as well as perennial systems in managed grazing or set-aside programs. Understanding how these practices influence soil health is critical for preventing further degradation, rehabilitating degraded soils, and fostering long-term agricultural sustainability.
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Title: What controls the composition of lawsonite?: host rock vs. external fluid sources
Authors: Erin Hudson, Sara Hanel, & Donna Whitney
Keywords: Lawsonite, fluid-rock interactions, subduction zones, element cycling
Abstract: Lawsonite (CaAl2(Si2O7)(OH)2*H2O) is a high-pressure/low-temperature mineral that plays a key role in H2O and element cycling in subduction zones. The fluids present during lawsonite growth may originate from the host rock and/or metasediment and serpentinite, and the composition and zoning of lawsonite may record interactions with variable fluid sources within subduction zones. Specifically, by analyzing trace element and isotope abundances in lawsonite, it is possible to distinguish the source(s) of fluids present during lawsonite crystallization and growth. Previous studies propose fluids derived from metasediment are attributed to elevated levels of Zn, K, and Rb, and those from serpentinites are attributed to increases in Cr, Cs, Ni, and Ba. Transition metal (Fe, Cr, Ti) concentrations and zoning also commonly change in lawsonite and may reflect host rock and external fluid composition variations. To attempt to evaluate how lawsonite composition is influenced by host rock parameters (bulk composition, mineral assemblage) vs. different external fluid sources, ten lawsonite samples from cold subduction zones around the globe were investigated via petrographic and electron microprobe analyses. Host rocks include blueschist, chlorite-mica schist, eclogite, and quartz-carbonate veins, and lawsonite textures range from extremely fine-grained matrix lawsonite to coarse-grained vein lawsonite. Initial microprobe analysis conducted on pink lawsonite in blueschist and white-blue lawsonite in chlorite-white mica schist indicates Fe and Ti concentrations are higher in the former, whereas Cr concentrations are higher in the latter. These values provide preliminary insight into potential compositional variations within lawsonite derived from host rock and external fluid interactions and act as a baseline for the project’s extended analysis.
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Title: Understanding Complex Discharge Response of a Karst Aquifer in Southeastern Minnesota
Authors: Jenny Huang, Charles Soucey, John Barry, Tony Runkel, Chris Langevin, Peter K. Kang
Keywords: karst aquifer, numerical modeling, heterogeneous media, contaminant transport
Abstract: Karst aquifers– carbonate aquifers with subsurface flow dominated by secondary porosity– present a unique challenge when estimating the spatial distribution and residence time of contaminants due to the presence of high subsurface heterogeneity which alters groundwater flow rates and paths. Combining fieldwork and numerical modeling can help characterize the complex transport and discharge behavior of these systems. With this approach, we attempted to characterize the Bear Spring field site, an unconfined karst aquifer in southeastern Minnesota with nitrate and chloride contamination. Field data indicates that increases in groundwater levels are correlated with Bear Spring discharge events that may arise from the activation of conduits situated at higher elevations in the aquifer. Data also shows that the springshed is sensitive to recharge (precipitation) events, although this sensitivity varies seasonally. We developed a single-layer, equivalent porous media (EPM) MODFLOW model of the Bear Spring springshed and compared the modeled and observed discharge and groundwater elevations to measure the fidelity of the model. While the model is able to capture the timing of observed discharge events, it underestimates discharge magnitude. The model also fails to match observed groundwater levels, overestimating head response to recharge. Additionally, the year-over-year variation in calibrated flow parameters and contribution area indicates the dynamic nature of the springshed boundaries. The limitations of the EPM model demonstrate the need for a 3D multi-layer groundwater model that incorporates conduit flow and depth-variable heterogeneity to accurately capture the head-dependent, recharge-sensitive discharge behavior and dynamic springshed extent of the aquifer.
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Title: Paleoclimate Reconstruction Using Stable Isotopes of Pedogenic Carbonates From Three Eocene Basins in Western North America
Authors: Sirena B. Rygiel, Emily J. Beverly, Jarred T. Asselta, Andrew G. Flynn
Keywords: Hyperthermals, Stable Isotopes, Paleoclimate
Abstract: The College of Liberal Arts at the University of Minnesota supports undergraduate research through the Dean’s First Year Research Program. For this project Eocene pedogenic carbonate samples from three understudied basins, the San Juan, Williston, and Wind River Basins in New Mexico, North Dakota, and Wyoming, respectively, will be prepared and analyzed. These basins record hyperthermal trends in the carbon isotopes of pedogenic carbonate, which are crucial to studying Earth’s response to climate change. The Earth is currently warming, and it is poorly understood as to how the climate will respond to higher atmospheric CO2 and how humans will adapt. Samples were collected over field seasons between 2019 and 2024. Paleosols were sampled for pedogenic carbonates in stratigraphic succession to capture hyperthermal trends through time. The carbonate nodules are wet-polished using sandpaper which allows diagenetic carbonate to be identified using a stereomicroscope. After, the samples will be dried at 40°C and 10 mg of carbonate will be drilled using a dremel. The prepared samples will be sent to the Stable Isotope Lab at Rice University to be analyzed using isotope ratio mass spectroscopy (IRMS) for stable 𝛿13C and 𝛿18O isotopes. The new data will be cross-analyzed with existing isotope data collected from the San Juan Basin in New Mexico, the Bighorn Basin in Wyoming, and the global marine record of 𝛿18O benthic foraminifera. Our hope is that these new data will expand our knowledge of the landscape response to rapid increases in CO2 and increase our understanding of climate change.
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Title: Alteration of Magnetic Mineralogy in the Giants Range Batholith by the Duluth Complex
Authors: Celia Cortopassi, Zsuzsanna P. Allerton, Joshua M. Feinberg
Keywords: Duluth Complex, paleomagnetism, Giants Range Batholith, thermal alteration, oxide minerals
Abstract: During the Midcontinent Rift event (ca. 1.1 Ga) of the North American craton, the Duluth Complex (DC), a large mafic igneous intrusion, was emplaced adjacent to the Neoarchean Giants Range Batholith (GRB; ca. 2.7 Ga) in northeastern Minnesota, thermally altering the granitic country rock. The basal mineralized zone of the DC has been well-studied with regard to sulfide deposits, but the extent of alteration within the GRB footwall has not been as well-researched. Previous research has indicated the presence of sulfides around the DC-GRB contact, extending about a hundred meters into the GRB, and prior petrographic analysis has revealed textures consistent with contact metamorphism that diminish with distance from the contact. This project seeks to define the extent of alteration into the GRB and to further characterize the orientation of the intrusion. This project utilizes a profile of 13 outcrop samples from the GRB, which were collected systematically at distances between 100 and 4500 meters from the DC-GRB contact. We characterize changes in magnetic mineralogy as a function of distance from the DC-GRB contact using measured magnetic properties (susceptibility and parameters calculated from hysteresis loops and backfield curves), optical microscopy, and electron microscopy. These data reveal a distinguishable and consistent pattern in magnetic properties as a function of distance from the contact and distinct zones of textural alteration in oxide minerals. Patterns in small-scale magnetic properties broadly align with the large-scale trends seen in aeromagnetic data, including changes in magnetic properties co-located with mapped faults. Future work may include the collection of oriented samples for further paleomagnetic studies, and potential thermal modeling of the subsurface DC-GRB contact.
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Title: Early Eocene Stratigraphic Record Across the Wind River Basin, Wyoming
Authors: Jarred Asselta, Andrew Flynn, Mykola Stepchuk, Brynn Miller, Emily Beverly
Keywords: Paleosols, Paleoclimate, Sedimentology
Abstract: During the early Eocene, the Wind River Basin in central Wyoming was a dynamic fluvial landscape that was responding to both contemporaneous uplift during the Laramide Orogeny and fluctuating early Eocene climate patterns caused by rapid injections of CO2 into the atmosphere in what are called hyperthermal events. The early Eocene was marked by a series of hyperthermal events providing a useful deep-time analog for anthropogenically induced climate change. Previous work from the Bighorn Basin of northern Wyoming identifies multiple negative carbon isotope excursions during the Paleogene tied to atmospheric CO2 changes. This injection of CO2 into the atmosphere is linked to a global increase in temperature, but other coeval records are needed to understand the overall impact on the landscape. The Wind River Basin preserves an understudied early Eocene fluvial record which provides a unique opportunity to compare hyperthermal induced terrestrial environmental change in western North America. Previous work in the basin focused primarily on the sandstone and conglomerate portions of the fluvial record for the purpose of understanding paleogeography and the tectonic history of the region, but this project aims to expand the paleosol record to improve paleoclimate reconstructions. A high resolution stratigraphic analysis of multiple localities in the basin is needed to set the framework for future paleoclimate reconstructions. This project focuses on two sites in the Wind River Basin: (1) Hell’s Half Acre near the town of Casper in the east and (2) Painted Hills near the town of Dubois in the west. The Indian Meadows and Wind River Formations have previously been interpreted to represent braided fluvial systems, but age control in the early Eocene is limited to biostratigraphy from mammals and maximum depositional ages from detrital zircons. Ongoing work to develop an early Eocene magnetostratigraphic age model for the Wind River Basin will aid in correlation to basinal, regional, and global records. Our preliminary stratigraphic work indicates that the depositional environments for the sites consist of braided channel systems and their associated floodplains with moderate- to well-developed paleosols identified as paleo-vertisols with abundant carbonate nodules appropriate for paleoclimate proxies. Future work with the paleosols will consist of traditional δ13C and δ18O stable isotopic measurements and Δ47 clumped isotopic measurements.
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Title: Stoichiometric modulation of zooplankton grazing on organic matter biogeochemistry
Authors: Ziyu Guo; Katsumi Matsumoto
Keywords: Stoichiometric modulation; biogeochemistry
Abstract: Recent studies shows the C, N, and P stoichiometry in marine phytoplankton tends to be higher than Redfield ratio (C:N:P=106:16:1) in oligotrophic waters, whereas zooplanktons are typically homeostatic and maintain C:N:P ratio fairly close to the Redfield ratio. The stoichiometric imbalance between zooplankton and phytoplankton can drive a grazing preference based on C:N:P ratio(food quality). There have been multiple global modeling studies that investigated the grazing preference effects on organism abundance. However, few studies have explored its impact on the carbon cycle, particularly in the context of both 0D and 1D models. We propose that zooplankton's grazing preference for prey can have significant biogeochemical consequences, including shifts in organism stocks within the biosphere, alterations in nutrient cycling, and impacts on carbon export and sequestration. By conducting a series of experiments with varying food quality sensitivities on the ideal 0D and 1D models, we thoroughly explore the biogeochemical consequences.
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Title: Late Holocene Primary Productivity Changes in the Cascadia Basin (NE Pacific): a Biogenic Silica Sedimentary Record
Authors: Sophie Davis, Vincy Winifred, Vera Pospelova
Keywords: biogenic silica, sediment core, northeastern Pacific Ocean
Abstract: The biogenic silica (BioSi) record has been studied at a centennial resolution to identify variability in Late Holocene primary productivity as a response to climate change in the northeastern Pacific region. We investigate how climatic and oceanographic changes over the past ~5,000 years have influenced marine primary productivity in the Cascadia Basin by analyzing the sedimentary BioSi content in 33 samples from the ONC-OYO98 core. The 47cm-long sediment core was collected by Ocean Networks Canada in 2016 using a remotely operated vehicle. BioSi, often referred to as biogenic opal, is a widely used geochemical proxy for identifying past abundances of diatoms, a major group of primary producers in marine environments. To measure BioSi sedimentary content, ~3 cc of sediment was subsampled and desalted by rinsing with reverse osmosis (RO) water. After rinsing, the samples were centrifuged at 3600 rpm for 6 minutes, and the water was decanted. All samples were then freeze-dried and hand powdered. The BioSi content was determined using a standardized protocol based on the work of Mortlock and Froelich (1989). This wet-alkaline extraction method, also known as the molybdate-blue spectrophotometric method, involves extracting silicates from sediment samples using sodium carbonate (Na₂CO₃). This process dissolves BioSi while minimizing contamination from aluminosilicates. We are currently presenting only preliminary results from the UROP-supported study. Once completed, this research will contribute to a better understanding of how marine primary productivity has responded to environmental changes in the past, which is important for predicting the impacts of future climate shifts.
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Title: Imaging the Magnetization of Archaeological Ceramics Using Quantum Diamond Microscopy
Authors: Sophie Wright, Maxwell Brown, Joshua Feinberg
Keywords: Quantum Diamond Microscopy (QDM), Magnetic sources, Ceramics Production phases, Ferromagnetic minerals, Microstructure, Magnetic flux mapping, Scanning electron microscopy (SEM), Bulk rock magnetic measurements
Abstract: Quantum Diamond Microscopy (QDM) can be used to directly image magnetic sources within a variety of different materials. This technique exploits the quantum properties of nitrogen vacancy (NV) centers in a synthetic diamond to optically detect magnetic resonance across a material. This resonance data can be used to construct a map of magnetic flux over an area of 4mm². In this study, we apply QDM to map the distribution of micron to submicron magnetic sources within six ceramics from southwestern Minnesota covering the past two millennia. The deaccessioned ceramic sherds were provided by the Science Museum of Minnesota, and were collected during excavations in 1973. The ceramics are typical of six known production phases in Minnesota. Differences, for example, are in the type of tempers used to strengthen the ceramics and in the methods used to mold them. Composite QDM maps were constructed to image full cross sections of sherds typically 1cm in length. By integrating QDM maps with reflected light microscopy, scanning electron microscopy (SEM), and bulk rock magnetic measurements, we aim to determine whether magnetic minerals are uniformly distributed within ceramic fragments and how these distributions relate to ancient production techniques and usage histories. Preliminary results indicate that ferromagnetic minerals are heterogeneously distributed within the ceramic sherds, which may be related to microstructural differences from the known production phases through time.
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Title: Evaluating Boreal Peatland Mercury and Methylmercury Responses to Increasing Temperatures and Carbon Dioxide
Authors: Connor Buckley, Cole Stenberg, Brandy Toner
Keywords: Mercury, Methylmercury, peatlands, climate change, boreal peatlands
Abstract: Mercury (Hg) is an important and potentially dangerous contaminant that exists in boreal peatlands. Peatlands’ anoxic conditions allow sulfate-reducing bacteria to methylate Hg into its toxic, organic form, methylmercury (MeHg). MeHg bioaccumulates in aquatic systems and can poison humans if contaminated fish are consumed. Peatlands hold a significant amount of both Hg and MeHg, but the question of whether mercury will be retained in peatlands during climate change is still to be answered. This project investigates how peatlands’ Hg and MeHg levels change in response to elevated carbon dioxide (CO2) concentrations and increased temperatures, which reflect the climatic conditions of the Earth in the coming years. Samples for this project came from the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project in Marcell, Minnesota. Experimental plots in this project are designed to mimic possible climate change outcomes. A range of temperatures will be used to observe how boreal peatland Hg and MeHg respond. In experimental chambers, air and soil temperatures are elevated at varying intervals, and each temperature-treated chamber has an increased CO2 counterpart. Porewater samples are collected at regular intervals and are analyzed via Cold Vapor Atomic Fluorescence for Hg and MeHg concentrations. Obtaining these values will allow us to determine how Hg and MeHg concentrations in peatlands will behave as the Earth warms and CO2 levels rise. Using this information, appropriate policy and management decisions can be made in Minnesota boreal peatlands to reduce health risks and to best preserve these important ecosystems.
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Title: Investigating the effect of plant species and soil geochemical properties on rhizosphere soil lead (Pb) concentrations in Twin Cities public parks
Authors: Madeline Taylor, Cara Santelli
Keywords: Urban environment, soil, rhizosphere, geochemistry, Pb
Abstract: Urban green spaces in Minneapolis and Saint Paul, MN are potential hotspots for lead (Pb) exposure due to the historical use of leaded paint and gasoline, and industrial practices like smelting and waste incineration. In soil environments, Pb undergoes chemical reactions driven by mineral reactivity, soil particle size, organic matter percentage, and pH changes that alter Pb speciation. Here, we collected rhizosphere soil samples from seven plant species across eleven public parks in the Twin Cities metro area and constructed linear regression models with a subset of 110 samples to determine significant relationships between plant species, soil geochemical properties, and bioavailable Pb concentrations. Total soil Pb concentrations were determined via x-ray fluorescence spectrometry (XRF) and ranged from 7.0 to 887 ppm (the EPA action level for soil Pb is 200 ppm). Soil carbon and nitrogen content, cation exchange capacity (CEC), and pH were measured through dry combustion, spectroscopy (ICP-OES), and electrode probe methods respectively. We found that plant species do not have a significant effect on soil C/N ratios (p = 0.81), CEC (p = 0.68), or pH (p = 0.22), while the sampling location has a significant effect on soil C/N ratios (p=5.48e-14), CEC (p = 1.23e-05), and pH (p = 5.96e-06). Total soil Pb concentrations were not affected by pH (p = 0.94), but showed a moderate correlation with CEC (p = 9.98e-08, correlation coefficient = 0.47), C% (p = 1.64e-14, correlation coefficient = 0.55), and N% (p = 1.42e-10, correlation coefficient = 0.63). A mixed effects model shows that plant species as a fixed effect on total Pb is not significant when sampling location is a random effect (p-value = 0.49). Based on model results, the sampling location, and therefore the park’s land-use history, has greater influence on soil Pb accumulation and geochemical properties than plant species.
Talk Abstracts
Title: Can climate resilient agricultural systems be developed to withstand Minnesota's shifting hydrologic regimes?
Authors: Lauren Bilek; Advised by Dr. Jessica Gutknecht
Keywords: Sustainability, agriculture, climate change, perennial, cover crops, soils
Abstract: Since 1895, Minnesota has experienced an increase of over three inches in annual precipitation and a rise in temperature of approximately 3℉. These trends are expected to persist, heightening the urgency to explore strategies that can safeguard our climate. A primary concern is ensuring the continued production of food, feed, and biofuels. To address this challenge, it is essential to investigate innovative agricultural approaches, including introducing novel perennial crops and cover crops. Our research specifically examines how different cropping systems influence soil health under various climate conditions. We focus on four cropping systems: conventional corn-soybean (C-S) rotations, both with and without cover crops, and the perennial grain Kernza™ (Thinopyrum intermedium), also with and without cover crops. These systems are subjected to four climate treatments, which involve manipulating water availability in the plots to mimic drought and flood conditions. Our study aims to understand how these cropping systems manage water, impact soil aggregation, and influence nitrate levels through leaching. The central question driving our research is whether climate-resilient agricultural systems can be developed to better withstand Minnesota’s changing climate.
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Title: Deciphering Solute and Reactive Transport in Triple Porosity Systems: Etched Rock Core Experiments and Numerical Modeling
Authors: Charles Soucey, Collin Sutton, Weipeng Yang, Christopher Zahasky, Peter K Kang
Keywords: Reactive transport, Carbonates, Triple porosity, Core Flooding, Imaging, Numerical Simulations, Hydrogeology, Karst
Abstract: Understanding solute and reactive transport in triple porosity systems—comprising conduits, fractures, and a porous rock matrix—is essential for a wide range of subsurface processes and applications. The inherent heterogeneity of these systems, along with solute exchange between high and low permeability regions, results in anomalous transport, including early solute arrivals and prolonged residence times. A key challenge in studying these processes is the inability to directly observe subsurface transport mechanisms. To overcome this, we employed etched dolostone cores with controlled geometry in reactive transport experiments and applied Positron Emission Tomography (PET) imaging to directly visualize solute transport. Our findings demonstrate that flow rate significantly influences solute exchange between the conduit and the fracture/matrix. PET imaging and reactive transport experiments reveal distinct solute and mineral precipitate distributions under low- and high-inertia flow conditions. Numerical simulations further highlight the role of fracture aperture in modulating solute exchange and show how higher flow rates induce 3D recirculation zones that enhance local reactivity. Tracer breakthrough curve inversions indicate that increased exchange can produce multi-peaked breakthrough curves. This multi-methodological approach—integrating etched core experiments, PET imaging, and numerical simulations—advances our understanding of solute and reactive transport processes in triple porosity media.
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Title: Distribution Of Geochemical Proxies Of Marine Primary Productivity In The Northern Part Of The Bering Sea: Implications For Paleoenvironmental Reconstructions.
Authors: Vincy Winifred, Vera Pospelova, Evangeline Fachon, Kenneth Neil Mertens, Zhen Li and Donald M. Anderson
Keywords: Bering Sea, Biogenic silica
Abstract: The northern part of the Bering Sea is a highly productive marine ecosystem characterized by dynamic and complex oceanographic conditions. In this study, we investigated geochemical parameters properties of surface sediments and their spatial variability across four distinct regions in the studied section of the Bering Sea: South Bering Strait, Norton Sound, North Inner Shelf, and North Middle Shelf. To understand sediment composition, sources of organic matter, and patterns of marine primary productivity, several geochemical proxies were measured, including total organic carbon (TOC) content, total nitrogen (TN), stable carbon isotope (δ¹³C) composition, and biogenic silica (Opal %). Our results revealed significant spatial heterogeneity across the region, with the North Middle Shelf exhibiting distinctly higher TOC (0.94-1.88%), TN (0.13-0.27%) and biogenic silica (10.72-19.70%) content. The stable carbon isotope (δ¹³C) composition ranged from -19.82‰ to -24.95‰ across the study area, with notably depleted values in the Norton Sound region (~-24.9‰) suggesting terrestrial influence from local river systems. The TOC/TN ratios and δ¹³C values pointed towards predominantly marine organic matter sources in the South Bering Strait, North Inner Shelf, and North Middle Shelf. A positive relationship between biogenic silica content and water depth (R²=0.693, p<0.01), as well as between biogenic silica and TOC (R²=0.836, p<0.01) were also observed. We found a positive correlation between sedimentary biogenic silica and the concentrations of cysts produced by heterotrophic dinoflagellates. This reflects a known trophic relationship where diatoms (a major source for biogenic silica) serve as preferable prey for heterotrophic dinoflagellates. We performed particle tracking modeling that revealed distinct trends in the lateral transport of sedimentary dinoflagellate cyst assemblages, with some sites showing isolated clusters (local influence) while others displayed more scattered regional distributions. Despite a nearly 20-year gap between this study and previous investigations in the region, the observed geochemical trends remain consistent with earlier findings (Stein et al., 2004). The comprehensive geochemical data from this work provide valuable insights into the modern sedimentation processes and organic matter sources in the northern part of the Bering Sea.
Reference: Stein, R., Stein, R., & MacDonald, R. W. (2004). The organic carbon cycle in the Arctic Ocean.
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Title: Earthquake distribution and the subducting slab thermo-petrologic structure beneath southern Colombia
Authors: Benjamin Knott-Byars, Ikuko Wada, Brandon Bishop, Linda Warren, Sungwon Cho
Keywords: Geodynamics, Subduction, Modelling, Fluids, Earthquakes
Abstract: We develop 2-D thermo-petrologic models for two transects through the southern Colombia subduction zone and compare the model-predicted temperature distributions and stability zones of hydrous minerals with seismological observations. One transect is through the Cauca region, where the seismicity in the relatively young subducting Nazca slab (10–12 Ma) is overlain by two groups of seismicity at <80 km and 90–145 km depths. The shallower and the deeper supra-slab groups are interpreted to occur in an accreted oceanic terrane and in the overriding mantle wedge, respectively. The other transect is south of the Cauca region, where both supra-slab groups are absent. The Vp/Vs in the slab are on average 1.78 and 1.76 along the north and south transects, respectively, with locally higher values of up to 1.95 along the northern transect. The Vp/Vs in the region of the deeper supra-slab group along the northern transect is ~1.78. These relatively high values likely indicate dehydration in the subducting slab and the addition of slab-derived fluids in the mantle wedge. We construct the thermo-petrologic models, using seismologically inferred slab geometries and lithological boundaries. To provide the relatively cool condition (<700ºC) for the observed seismicity, the maximum depth of decoupling (MDD) between the subducting slab and the overriding mantle needs to be anomalously deep, at ~180 and ~130 km depths for the northern and southern transects, respectively. With these MDDs, the model-predicted thermal fields result in slightly deeper peak dehydration in the subducting slab along the northern transect than the southern transect, affecting the distribution of slab-derived fluids in the subduction zone. The difference in the MDD between the two transects may explain the contrast in the distributions of intraslab and supra-slab seismicity between them.
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Title: Re-evaluation of oriented and faceted inclusions in garnet as indicators of Ultrahigh Pressure/ Temperature metamorphism
Authors: Sithari M Nanayakkara, Donna L Whitney, Christian Teyssier
Keywords: Oriented rutile needles, faceted negative crystals
Abstract: The presence of oriented rutile needles and faceted, negative crystals of quartz, plagioclase and other minerals in garnet is considered diagnostic of extreme metamorphic conditions, particularly in ultra-high temperature (UHT) and/or ultra-high pressure (UHP) terranes. However, a few instances exist where such inclusions occur in rocks lacking other evidence for extreme conditions. The sillimanite gneisses from the Skagit Gneiss Complex of the North Cascade Range (USA), which contain faceted- and oriented- inclusion bearing garnets, record peak metamorphic conditions of ~1 GPa and 725°C and therefore showing significantly low pressure and temperature conditions than most other occurrences of garnets containing such inclusions. The Barrovian metamorphic sequence in Dutchess County, NY (USA) also reports lower pressures (P < 1 GPa), yet it contains these characteristic oriented rutile needles and faceted plagioclase/quartz inclusions. This study investigates the formation mechanisms of faceted and oriented inclusions in garnets from these two terranes to refine constraints on their P–T conditions and assess whether these textures are truly diagnostic of extreme metamorphism. Petrographic analysis, electron probe analyses (EDS, WDS, BSE), and electron backscatter diffraction (EBSD) mapping are used to characterize the inclusion-garnet relationships and evaluate possible post-entrapment modifications of the garnets with these inclusion textures. The ongoing work will help determine whether the existing P–T estimates for these localities are underestimated or whether these textures, conventionally linked to UHT and UHP metamorphism, can also develop under more moderate conditions.
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Title: Petrofabric investigation of the sulfide-rich basal Duluth Complex
Authors: Ishmael Cobbinah, Christian Teyssier and Donna Whitney
Keywords: Duluth Complex, Mafic Intrusion, Fabrics, Sulfide deposits, Mineralization, AMS, XCT, EBSD
Abstract: At 1.1 billion years ago, the Midcontinent Rift nearly split the North American craton and produced voluminous magmatism. During this event, the Duluth Complex (NE Minnesota) formed as a large mafic intrusion into Archean granitoid basement (Giants Range Batholith) and Paleoproterozoic sedimentary rocks, hosting significant Cu-Ni-PGE sulfide deposits concentrated within ~400 m of its basal contact. Although the geochemistry and petrology of these deposits are well studied, the physical processes of sulfur-rich magma emplacement remain poorly understood. This study investigates whether dynamic magma flow (which produces mineral alignment or fabrics by shearing) influenced sulfide mineralization by transporting immiscible sulfide droplets within a flowing crystal-rich mush prior to deposition.
We analyzed oriented drill core samples from ten closely spaced sites spanning mineralized and unmineralized zones. Anisotropy of Magnetic Susceptibility (AMS) measurements reveal a dominant oblate (flattened) magnetic fabric with alignment that is strongest near the basal contact where sulfide mineralization occurs, and weaker in more distant unmineralized zones. Fabrics in the ore-bearing interval are also more variable in orientation, indicating a highly dynamic (likely turbulent) magma flow regime. Such vigorous flow likely ensured thorough mixing of sulfide droplets into the silicate melt, enhancing scavenging of chalcophile metals and promoting ore formation. Guided by the AMS results, thin sections are prepared from cores for EBSD analysis to measure plagioclase crystallographic orientations and compare them with magnetic fabrics. Preliminary petrography and energy-dispersive X-ray spectroscopy (EDS) indicate that chalcopyrite and pyrrhotite occur as inclusions within plagioclase and pyroxene, typically associated with Fe-rich biotite. Initial high-temperature magnetic susceptibility results suggest magnetite is a major contributor to the AMS fabric, with possible influence from pyrrhotite, though further confirmation is needed. Additionally, we are using 3D X-ray computed tomography (XCT) to visualize sulfide sizes and distribution and fabric (if any) in gabbroic cores of varied textures. As analysis continues, this study aims to integrate all data to explore potential correlations between flow fabrics and sulfide mineralization in mafic layered intrusions.
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Title: A new microphysical model for dislocation-mediated seismic-wave attenuation in the upper mantle
Authors: Diede Hein, Thomas P. Breithaupt, David Wallis, Lars Hansen
Keywords: Attenuation, upper mantle, olivine
Abstract: Observations of seismic-wave attenuation are often used to interpret conditions in the upper mantle, including temperature, grain size, and melt or water content. However, these interpretations require a detailed understanding of the physical mechanisms that cause seismic-wave attenuation. Despite considerable effort over the last three decades, a physics-based micromechanical model that can explain both laboratory attenuation experiments and seismological observations remains elusive. Forced-oscillation experiments on polycrystalline olivine and surface-wave studies indicate that attenuation scales weakly with frequency, resulting in a ‘dissipation band’ over seismic frequencies and amplitudes. Previous studies have invoked the mechanism of grain-boundary sliding, accommodated either elastically or diffusively, in conjunction with spatially heterogeneous grain-boundary geometries in polycrystalline olivine to explain this weak frequency dependence of attenuation. However, at present, there has been no self-consistent demonstration that a given distribution of grain geometries in a mantle rock leads to the frequency dependence of attenuation observed for that rock. We proffer an alternative hypothesis that elastic interactions among dislocations in olivine may be able to explain the observed viscoelastic behavior of the upper mantle. This model is known as the backstress model after the restoring force that the elastic interactions among dislocations generate and has been successfully applied to model the anelastic behavior of olivine in the laboratory over a wide range of temperatures. Here we present an extension of the backstress model to explain the weak frequency dependence of seismic-wave attenuation. The extended backstress model incorporates the intragranular spatial heterogeneity of backstresses in olivine to explain the anelastic response of olivine over a wide frequency range. We demonstrate that our model can produce a dissipation band consistent with the magnitudes of attenuation observed in the upper mantle for reasonable temperatures, dislocation densities, and stress heterogeneities. A significant implication of our model is that seismic-wave attenuation in the upper mantle may be more sensitive to variations in dislocation density, and tectonic stress history, than to variations in grain size.
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Title: Re-core-ds of Paleoclimate from Paleosols in Baringo Basin, Kenya
Authors: Madison Rafter, Emily J. Beverly, William Lukens, Kathryn Snell, John Kingston, and Carly McCarthy
Keywords: Paleoclimate, Paleosols, Sedimentology, Stable Isotopes
Abstract: Baringo Basin, Kenya, in the Eastern African Rift, preserves the most continuous record of fossiliferous Neogene strata in equatorial Eastern Africa. The BTB13 sediment core was drilled in Baringo Basin through Plio-Pleistocene paleolake strata (3.29 Ma - 2.56 Ma) and records two major climatic events: 1) the mid-Pliocene Warming Period (mPWP; 3.25 - 2.95 Ma) which is an important analogue for modern climate change, and 2) the onset of global cooling leading to the Northern Hemisphere Glaciation (NHG; ~2.75 Ma). Paleosols (n = 78) compose 57% of the 222.6 m core length from lacustrine, fluvial, alluvial, and tephra units. The paleosols were measured for the abundance of stable carbon and oxygen isotopes in pedogenic carbonates (δ13CPC and δ18OPC) to track hydrologic and environmental changes like C4 plant abundance. δ13CPC ranges from -11.7‰ to 4.5‰ VPDB (mean = -6.4‰) and shows a transition from shrubland to wooded grassland and C4 grasslands in Baringo Basin as NHG intensified. δ18O serves as a proxy for paleoprecipitation and changing seasonality due to shifts in the Eastern African Monsoon– the region’s dominant precipitation regime– and ranges from -15.5‰ to -0.3‰ VPDB (mean = -4.6‰). δ18OPC depends on the δ18O of precipitation, the δ18O of soil water (δ18Osw), and the soil temperature (TΔ47), which can be calculated using carbonate clumped isotopes (Δ47). Eight Δ47 samples were run to reconstruct TΔ47 and the δ18Osw through the core length. TΔ47 data, ranging from 15 to 29℃ (mean = 22℃), shows a gradual cooling trend (~8℃) as glaciation intensified with warmer temperatures (~26℃) correlating with the mPWP. Reconstructed δ18Osw values range from 2.9 to -3.2‰ VSMOW (mean = -1.1‰) and show fluctuations in the hydrologic cycle but no long term trend. Changes in vegetation and paleotemperature broadly correlate with known increases in temperature and pCO2 from global climate events, but further Δ47 analyses are needed to refine correlations. Ongoing work on the bulk and clay mineralogy (XRD) of the paleosols will also provide insight into environmental suitability for early hominins as soil fertility is influenced by soil salinity and mineralogy.
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Title: Assessing blue oak (Quercus douglasii) growth resilience to extreme drought across fine-scale topography in California
Authors: Sandy K. K. Wong, Daniel Griffin, Matthew L. Trumper, Zachary Principe & Michael D. White
Keywords: Dendrochronology, forest resilience, drought, mountain geography, global change biology
Abstract: Extreme hot temperatures and low precipitation were observed in California, especially during the past two decades. The combination of the two factors increase the frequency and intensity of drought events across the state. Many forest ecosystems within the state, including the drought-tolerant blue oak (Quercus douglasii)-dominated savannas and woodlands, have exhibited signs of drought stress and mortality. Despite some literature addressing the role of topographic position in mediating climate-tree growth relationships, few studies have focused on blue oak drought responses across topoclimate gradients. Tree-ring chronologies were developed from 81 blue oak individuals sampled from five topographic positions, which were selected along water year mean climatic water deficit gradient (potential minus actual evapotranspiration). To characterize tree growth response to extreme drought events in the 20th and 21st century, Lloret and Schwarz drought resilience indices were calculated and evaluated, examining tree growth before, during, and after droughts. Climate responses analysis was implied to identify climate variables that have significant influence on tree growth. The application of multiple indices provides the most holistic assessment of tree growth response to drought: it provides the information of the exact growth reduction during extreme drought, and time required to recover to pre-drought stage. Blue oak growing in drier sites had higher tree growth reduction (low resistance), high but slow recovery, long recovery period and lower drought resilience. Precipitation appears to be the most dominant climatic factor for blue oak growth. However, temperature has become increasingly influential in recent years. The phenomenon is more evident in higher elevation regions. Although blue oak in wetter sites had higher drought resilience, the increasing temperature influence on tree growth, as well as the disproportionate temperature rise at higher elevation, may increase the drought severity in wetter sites and vulnerability of these populations in future decades.
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Title: A Comparison of Methods for Estimating Excess Ice Content in Permafrost-affected Soils
Authors: Megan L. Andersen, Nicolas A. Jelinski, Julie D. Jastrow, Mikhail Kanevisky, Yuri Shur, Chien-Lu Ping, Torre Jorgenson, Roser Matamala
Keywords: excess ice, permafrost-affected soils, subsidence risk
Abstract: Accurate quantification of excess ice in permafrost-affected soils is essential for predicting ground subsidence during permafrost thaw - a critical factor in infrastructure stability and ecosystem modeling in Arctic regions. Excess ice, defined as volumetric ice content exceeding soil pore space, directly determines subsidence potential, yet estimation methods vary significantly in approach and accuracy. Our study evaluates four methods for determining excess ice content: direct measurement through sample thawing and water extraction; calculations based on physical soil properties; computational approaches using pedotransfer functions; and visual estimates. Each presents distinct advantages in different field scenarios and resource constraints. While direct measurement provides the reference standard, our findings reveal that visual estimation of excess ice correlates strongly with direct measurements. This offers significant practical implications for rapid field assessment and remote analysis. Computational methods show varying effectiveness depending on soil characteristics. This comparative analysis provides critical guidance for permafrost researchers and modelers seeking to improve subsidence predictions in thawing landscapes. By identifying the most effective and efficient estimation techniques across diverse permafrost conditions, our work enhances the accuracy of climate change impact assessments in vulnerable polar regions.
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Title: Developing a Climate Classification Framework for Antarctica: Integrating Reanalysis, K-Means Clustering, and In-Situ Observations
Authors: Julia R. Andreasen and Peter D. Neff
Keywords: Antarctica, climate classification, reanalysis data
Abstract: There are currently no detailed classification systems specific to Antarctica’s range of extreme temperatures, variable precipitation rates, and dynamic wind speeds. The Köppen classification broadly categorizes Antarctica as EF (ice cap climate), with continuous subzero temperatures and minimal precipitation, while some coastal areas, like the Antarctic Peninsula, may fall under ET (tundra climate) due to occasional summer warming. However, these broad categories overlook the continent’s diverse climate variability. Although there is some regionally focused research that analyzes Antarctic microclimates and specific meteorological phenomena, these studies also do not establish a comprehensive classification framework for the entire continent. Here, we create an Antarctic-specific classification system based on k-means clustering of ERA5 modeled reanalysis datasets (from 1979-2023). This classification identifies eight distinct climate zones based on annual and seasonal averages of temperature, precipitation, and wind speed. These classifications range from the hyper-arid and frigid polar plateau zone (zone 1), where annual temperatures reach as low as -62.52°C and precipitation is near zero, to the dynamic subpolar coastal transition zone (zone 8), where temperatures can exceed freezing, precipitation can average up to 1.73 m annually and winter wind speeds surpass 14 m/s. To further validate our classification, we compare it against the MetReader dataset, which provides field-based temperature data from 53 weather stations across Antarctica. The comparison between the ERA5 reanalysis and MetReader observations helps to refine the clustering and ensures the robustness of our climate classification. Overall, this study fills a critical gap by establishing a continent-wide framework for defining climate zones, improving our understanding of regional climate patterns across Antarctica and capturing the spatial and seasonal variability.
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Title: Analyzing the factors that affect forearc stresses using numerical models
Authors: Viven Sharma and Ikuko Wada
Keywords: Subduction zones, Forearc stresses, Numerical modeling
Abstract: We investigate the state of stress in the forearc region of subduction zones using 3-D mechanical finite element models for the forearc system force balance. Using the mechanical models for generic forearc systems with a range of model parameters, we investigate the effects of these two parameters (i.e., the downdip depth and width of plate coupling) as well as the fault strength, surface topography, and forearc width on the inner forearc stress state. 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. Our numerical model consists of an elastic overriding crust, an elastic mantle wedge corner, and a viscoelastic mantle layer. In the model, we apply the densities and the mechanical properties appropriate for the lithologies assumed in the model, including the mantle wedge corner, to incorporate their effects on forearc stresses. Our numerical modeling results indicate that the forearc tends to be in compression in subduction zones with a deeper downdip extent of plate coupling.
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Title: Investigation into the mobility and chemical forms of lead pollution in Twin Cities stormwater catchment ponds using synchrotron based X-ray absorption spectroscopy
Authors: Christof Zweifel, Lea Pollack, Ben Janke, Jacques Finlay, Emilie Snell-Rood, and Cara M Santelli
Keywords: X-ray absorption spectroscopy, lead pollution, stormwater catchment ponds
Abstract: The Minneapolis-St. Paul Metro Area is impacted by various lead sources including emissions from the downtown garbage burner, regional airports, smelters, lead paint, and the legacy of leaded gasoline. Lead in urban runoff enters catchment ponds that are often chemically- and physically-stratified, and may undergo geochemical transformations that determine lead concentration, chemical speciation, and bioaccessibility. Lead concentrations in the sediment of a sample set of over 30 catchment ponds range from 10 to 2,000 ppm, measured using X-ray fluorescence (XRF). Surface water, bottom water, and sediment porewater measured using inductively coupled plasma - mass spectrometry (ICP-MS) range from below detection to 0.002 ppm dissolved lead. Lead is predominantly in sediment, not in pond water, but has the potential to be remobilized during pond turnover and mixing or when sediment is dredged. Lead within sediments and soils consists of a variety of mineral forms or adsorbed to iron oxyhydroxides and organic matter. Each form of lead is either from the source pollutant or formed during soil weathering, offering insight into potential hazards and transformation pathways. Synchrotron based X-ray absorption spectroscopy (XAS) is uniquely able to distinguish components within the sediment bound lead, and provide an average composition for soil and sediment samples. A principal component analysis (PCA) of XAS spectra revealed different major components used to describe soil samples versus sediment samples. The fitting of the XAS spectra reveals that lead sulfide is found in higher proportions within pond sediments, and pond sediments have lower proportions of lead bound to iron oxyhydroxides. The capture of metals in ponds has important implications for urban ecology and management such as defining trends in lead concentration and bioaccessibility within urban watersheds, determining how to best maintain and dredge catchment ponds, and store the potentially hazardous waste.