2019 Gala

April 3-5, 2019

Keynote speaker: Breanyn MacInnes (ESS '10)

Main website

Schedule

Wednesday, April 3 :Poster Session

1:30-4:30 JHN 1st Floor

Gabrielle Alampay : Interpreting Haida Gwaii's Marine Terraces Using LIDAR Data
Surabhi Biyani : Estimating the Upper Bound of Crustal Heat Flow under Antarctica
Fred Bradley : Ice Polymorph Formation and Segregation Within High-Pressure Icy Mantles of Watery Moons
Cassie Brigham : Examining the causes of degredation of fault scarps in Iceland
Elizabeth Davis : Evidence for earthquakes from the Duwamish Waterway, Seattle
Connor Geiman : Designing a Reliable Asteroid Sample Retrieval System
Gabriel Goncalves : A New Drepanosauromoph Species from the Chinle Formation of Petrified Forest National Park, Arizona
Monica Hill : Constraining Slip Rates Along the Seattle Fault Zone Using Low Temperature Thermochronometry
Brita Horlings : Modeling firn densification through the evolution of microstructural properties
Joel Jacobsen : Anthropogenic Influence on Reactive Chlorine in the Troposphere
Bing Yu Lee : Understanding the Temporal Variation of Methane Seepage at Southern Hydrate Ridge (SHR) using Acoustics
Joshua Lee : Buildup of Larges Scale Field Test for Asteroid Sampler
Alex Lowe : A project proposal: Ancient plant community and climate of the Pacific Northwest (USA) during the Middle Miocene Climatic Optimum
Zack McIntire : On the Hydrodynamics of Crystal Clustering
Megan Mueller : Post-Collisional Evolution of Western Anatolia: Tectonostratigraphy of the Saricakaya Basin
Haley Redinger : A Comparison of Growth Strategies by U-reducing Bacterium Shewanella putrefaciens CN32
Nicole Sarieddine : Determining the month of soil carbonate formation for paleoclimate reconstruction
Kelsay Stanton : Tectonic implications recorded by Pleistocene and older marine terraces above the Cascadia Subduction Zone, Willapa Bay, Washington
Max VanArnam : Modeling Monsoon Flood Erosion in the Eastern Himalaya: using HEC-RAS to simulate velocity and depth for high discharge annual flows

Thursday, April 4

9:00-10:30 - Session 1: All Things Life, Astrobiology/Paleontology (JHN 170)

9:00 Michael Kipp: Does the C/N ratio of organic matter in ancient marine sediments record dissolved oxygen levels?
9:15 Jana Meixnerova: Expanding our understanding of Archean life using transitional metal isotopes
9:30 Lucas Fifer: Habitability implications of high CO2, CH4, and H2 gas concentrations in Enceladus’ ocean
9:45 Hillary Smith: Environmental Controls on the Earliest Animal Ecosystems
10:00 Brody Hovatter: The early Paleogene rise of eutherians and decline of multituberculates and metatherians: Insights from analysis of dental disparity, morphospace occupation, and body size of earliest Torrejonian (To1) mammals from northeastern Montana, USA
10:15 Paige Wilson: Seafood Salad: A Diverse Florule from the Late Cretaceous-age Hell Creek Formation of Montana

10:30-10:45 Break

10:45-12 - Session 2: Ice World Hoth, Glaciology (JHN 170)

10:45 Ben Hills: Inferences from a subglacial lake at the South Pole constrain ice temperature and dynamics
11:00 Alex Huth: A comparison of ice fracture models
11:15 Taryn Black: A multidecadal record of outlet glaciers in northwestern Greenland
11:30 John Christian: The Clydesdale and the Whippet: Idealized investigations of marine-terminating glacier dynamics
11:45 Trevor Hillebrand: West Antarctic Ice Sheet fluctuations during Pleistocene super-interglacials

12:00- 1:45 Lunch Break

1:45-3:00 - Session 3: Afternoon Allochtons, Structure and Tectonics (JHN 170)

1:45 Jordan Wang: Evidence for Fault-Valve Behavior in Ultracataclasites of Carbonate-Hosted Normal Faults, Central Apennines, Italy.
2:00 Sarah Harbert: Exhumation and mountain building in the Marlborough Fault System, New Zealand
2:15 Carolyn Nuyen: Crustal Deformation Near the Mendocino Triple Junction Inferred From GPS-Derived Strain Rate Maps
2:30 Mattathias Needle: Reconstructing a folded surface: from point cloud to NURBS
2:45 Ginevra Moore: Shallow offshore deformation in the Seattle fault zone

3:00-3:30 - Seminar Snacks, snacks and freshments outside JHN 075

3:30-5:00 - Colloquium: Breanyn MacInnes, keynote speaker (JHN 075) "Using tsunami deposits to distinguish slip during earthquakes"

Friday, April 5

9:00-10:15 - Session 4: Shake, Rattle, and Roll, Seismology (JHN 170)

9:00 Ian Stone: Topographic response to ground motion from modeled Seattle Fault earthquakes
9:15 Kelley Hall: Induced Stresses on the Cascadia Megathrust during ETS Events and Implications for the Triggering of Tremor
9:30 Mika Thompson: Investigating the Performance of Earthquake Early Warning Algorithms on the Cascadia Subduction Zone
9:45 Ariane Ducellier: A two-year long catalog of low-frequency earthquakes for Northern California
10:00 Emma Myers: Downward Continuation Streamer Tomography: Exploring Shallow Plate Bending Faulting and Hydration

10:15-10:30 Break

10:30-11:30 - Session 5: The Final Frontier, Planetary & Space Science (JHN 170)

10:30 Todd Anderson: Monitoring radio wave attenuation in the Earth-ionosphere waveguide with the World Wide Lightning Location Network
10:45 Ping-Chun Lin: Investigating wetted slope streaks in the McMurdo Dry Valleys, Antarctica: Do similar flows form on Mars?
11:00 Sarah King: New evidence that seasonal flows on Mars are dry, windblown sand avalanches
11:15 Andrew Shumway: The formation of low temperature perchlorate brines in Martian soils

11:30- 1:00 Lunch Break

1:00-2:00 - Session 6: Some Like It Hot A, Geochemistry (JHN 170)

1:00 Tianyi Huang: Heterogeneous potassium isotopic composition of the upper continental crust
1:15 Yan Hu: Potassium isotopic heterogeneity in subducting oceanic slabs and implications for global K cycle
1:30 Addien Wray: Geochemical effects on the adsorption of uranium onto Shewanella putrefaciens CN32
1:45 Nicolas Wogan: The Chemical Disequilibrium of Non-Photosynthetic Worlds

2:00-2:15 Break

2:15-3:00 - Session 7: Some Like It Hot B, Geochemistry (JHN-170)

2:15 Joel Gombiner: Ice age flooding of Moses Coulee, eastern Washington
2:30 Mary Alice Benson: Sediment accumulation in a manipulated bay of Puget Sound, Bellingham, Wa.
2:45 Julia Kelson: Seasonality of soil carbonate accumulation: insights from a synthesis of modern-Holocene clumped isotope data and numerical modeling

3:00-3:15 - Break

3:15-4:00 Session 8: Quick, Quick, Do Tell Me!, Up-Goer 5(JHN-170)

3:15 Lindsey Davidge: Learning about the old sky by using a light box to find middle-big waters in ice sticks
3:25 Virginia Littell: High, low, heavy, light - using these things to tell us about how and when places that are high today got so tall
3:35 Tristan Bench: Assessing Surface Erosion Rates of Rocks in the Context of Petroglyph Preservation Analyses using Cosmogenic Isotopes
3:45 Marina Duetsch: The over filling of air with water and how it controls water same places

4:00-5:30 Break

5:30-9:00 - Reception and Closing Ceremony (Vista Cafe)

Poster Session

April 3rd, 1:30-4:30pm, JHN 100-level hallway

Gabrielle Alampay: Interpreting Haida Gwaii's Marine Terraces Using LIDAR Data

In this study, I map and consider possible driving mechanisms of marine terrace formation on the archipelago of Haida Gwaii, Canada. Marine terraces are gently sloping platforms created by wave erosion along shorelines, and are preserved through crustal uplift or sea level change. In the past, native people of the islands occupied areas along the now uplifted shorelines. Archeologists have found artifacts on some of these terraces and have dated them to be ~8,500-9,000 B.P.. Southwest of the islands, there is a young subduction zone, which produced a Mw 7.8 thrust earthquake in 2012 and has been hypothesized to drive uplift in Haida Gwaii. While the islands are ice free today, they hosted an ice cap during the last glacial maximum and were in the forebulge of the Cordilleran Ice Sheet. The islands may have also uplifted from isostatic rebound as a result of the ice melting. To identify the formations, I mapped marine terraces from 1,500 km2 of high resolution elevation topography derived from LIDAR data. In the data, I find terraces throughout the study area that extend up to 18 m above sea level. Typically, only one terrace is preserved and terrace heights are about the same elevation of ~15-18 m across the study area. From this study, we can find out more information about the terraces’ geometry, if there are spatial trends in elevation, size, and distribution in order to further our understanding of what is driving the land uplift. Identifying and studying Haida Gwaii’s marine terraces are important to help archaeologists date known terraces and help geologists better understand the tectonics of the area.

Surabhi Biyani: Estimating the Upper Bound of Crustal Heat Flow under Antarctica

Geothermal flux, the amount of heat from the Earth’s interior that reaches the Earth’s surface, is an important boundary value used when modeling ice sheets in Antarctica and estimating future sea level rise. However, geothermal flux is difficult to measure directly. This research project used a numerical ice and heat flow model to estimate the upper bound for geothermal flux under ice domes in Antarctica. We applied this model to ice domes with identifiable Raymond arches, structures in the internal stratigraphy which form only when the ice is frozen to the bed. We estimated the geothermal flux at which an ice dome’s modeled basal temperature reaches the melting point, thus setting an upper bound, using site-specific values for the accumulation rate, surface temperature, and ice thickness. Where measured basal temperatures are known, we made more precise estimates of geothermal flux. Uncertainty values for the modeled flux values were derived by testing the uncertainty of each input value. Model estimates were compared with Martos et al. (2017) and An et al. (2015) geothermal flux estimates derived from remotely sensed data. Comparisons show that in regions such as the Siple Coast, estimates disagree significantly, while they mostly agree in the Antarctic Peninsula. The results of this project set an upper limit on geothermal flux values that can be used to support past and future geothermal flux estimates at these locations.

Fred Bradley: Ice Polymorph Formation and Segregation Within High-Pressure Icy Mantles of Watery Moons

Understanding the subsurface dynamics and differentiation of icy moon interiors is critical for model development, future mission planning, and guiding the search for life beyond Earth. Icy moons such as Enceladus, Ganymede, and Europa contain enormous amounts of water that form kilometers thick icy crusts which cover massive liquid oceans. These waters also likely contain solutes (e.g. MgSO₄, NaCl, Na₂SO₄) leached from the underlying silicate mantles. As a result, the interiors of these icy worlds are thought to be differentiated ocean systems with layers of ices and water whose vertical partitioning is dependent on the relative densities of each phase and decreases in melting temperature with higher salt concentrations. The experiments performed in the ESS mineral physics laboratory at UW determine not only the phase of ice expected at pressures and temperatures found within icy moons but also measures melting temperature depression for each phase as a function of salt complex and concentration. Determination of phase boundaries was measured by manually nucleating ice crystals in a diamond anvil high-pressure cell at a given temperature while ruby fluorescence spectroscopy recorded the corresponding pressure. Samples of pure water, as well as 0.5 molal, 1 molal, and 2 molal concentrations of each salt solution were studied. From in-situ sound speed measurements and X-Ray diffraction data, a local basis function representation of the free energy (Gibbs) was used to calculate and extract thermodynamic data for each aqueous solution and ice phases. These results allow for further exploration and understanding of the behavior of salty waters within the interiors of icy moons. These relationships are important for understanding the spatial distribution and partitioning of ice and aqueous solution phases, the possible geodynamic drivers such as heat transport regime and density contrasts, and predictions about the state of the hydrosphere/silicate mantle boundary.

Cassie Brigham: Examining the causes of degradation of fault scarps in Iceland

Connor Geiman: Designing a Reliable Asteroid Sample Retrieval System

Elizabeth Davis: Evidence for earthquakes from the Duwamish Waterway, Seattle

The Duwamish Waterway in the city of Seattle provides clues to the city’s earthquake hazards. The industrialized banks of the waterway locally expose intertidal mud of the former Duwamish River estuary. These deposits contain evidence for two earthquakes in the centuries since the large Seattle Fault earthquake of 900–930. (All age ranges are in calibrated years CE at two standard deviations). The evidence consists of intrusions and extrusions of andesitic sand within the mud. These sand bodies were likely produced by earthquake-induced liquefaction of the Mount Rainier lahar-runout deposits that underlie the mud. The earlier of the two inferred earthquakes is evidenced by a sand layer that extends discontinuously for at least 50 m. This layer consists of coalesced sand lenses up to 12 cm thick. The layer coincides with the upper limit of parallel, mostly vertical sand intrusions interpreted as evidence for lateral spreading. The implied earthquake likely dates to 1010–1150, as judged from radiocarbon ages of growth-position Triglochin maritima leaf bases that one of the sand lenses drapes. At least one later earthquake is evidenced by dikes in younger mud. One of these dikes approaches the stratigraphic level of T. maritima leaf bases from 1250–1290. Other dikes nearby were traced up to Bolboschoenus maritimus corms from 1470–1640. None of the injected or erupted sand bodies observed thus far reach the likely stratigraphic level of the 1700 Cascadia earthquake or the Puget Sound earthquakes of 1949, 1965, and 2001. I am grateful for guidance by Brian Atwater, Juliet Crider, and Carrie Garrison-Laney; and for diatom analysis by Eileen Hemphill-Haley.

Gabriel Goncalves: A New Drepanosauromoph Species from the Chinle Formation of Petrified Forest National Park, Arizona

Drepanosauromorpha is an extinct group of reptiles known from the Middle to Late Triassic (237–212 MA). The clade currently includes seven genera (Avicranium, Dolabrosaurus, Drepanosaurus, Hypuronector, Kyrgzsaurus, Megalancosaurus, and Vallesaurus) that are known from fossils collected in Europe (Italy, UK), North America (Arizona, New Mexico, New Jersey), and Asia (Kyrgyzstan). The first described drepanosauromorph, Drepanosaurus unguicaudatus, was based on a flattened holotype preserving most of a complete skeleton. Subsequently described drepanosauromorphs contain some of the following features: the length of the chevrons is substantially longer than caudal (tail) neural spines, the cervical (neck) vertebrae are heterocoelous (saddle-shaped articular surface), the cervical ribs are absent as distinct ossiﬁcations and the chevrons are fused to the centra. In recent years, both three-dimensionally preserved partial skeletons and isolated material of drepanosauromorphs have been found across both Europe and North America. These discoveries have helped shape our understanding of the biology and diversity of drepanosauromorphs. However, comparing isolated, three dimensionally preserved specimens to the more complete, yet two dimensionally preserved articulated specimens is difficult due to differences in preservation. Here, we describe a new drepanosauromorph species from the Chinle Formation in Petrified Forest National Park, Arizona based on the ungual phalanx of the second digit of the hand. Some of the characteristics that distinguish this claw from most drepanosauromorphs is the size of the claw. It differs significantly from all known Drepanosaurus specimens (like the Italian holotype and the Hayden Quarry Drepanosaurus) because of the ventral placement of the cotyle, the height of the claw, the lack of compression along the pre-axial/post-axial plane and a furrow along the midline. This new taxon not only shows how much morphological variation there is within Drepanosauromorpha, but this taxon also helps create a clearer understanding of the evolutionary history of smaller-bodied reptiles within the Triassic.

Logan Guillet: Ice Crater Analysis Using Advanced Surveying Techniques

This research focuses on using advanced surveying techniques as well as hand mapping to analyze force distribution during laboratory impacts of man-made projectiles into ice. This is done in the hopes of characterizing substrate damage surrounding an impact crater created by a proposed hard landing system. Knowing where these different deformation zones occur is useful in determining where the lander could sample. The landing system, the Subsurface Ice Plume Sampler (SIPS) utilizes ejecta (broken up debris thrown from the crater) to create a transient atmosphere - decelerating a secondary instrument package through momentum transfer. Small-scale experiments were done on one-ton buckets of ice using scale-sized projectiles. Between two hundred and five hundred images used to 3D models of the ice craters using the structure from motion imaging technique. Hand mapping of the deformation zones (areas of different types of fractures) was conducted to compare to the 3D model to help show the directionality of force distributions through the crater. Using both the 3D models and a hand mapping analysis of the craters, we were able to determine that the crater shapes were atypical. In a typical crater, the force disperses radially outward from the impactor; however, we determined that the majority of the force was focalized directly below the impactor. Future work includes using Rhinoceros 3D computer software to quantitatively analyze each crater’s individual morphology, curvature, and volume and compare them to traditional impact craters.

Monica Hill: Constraining Slip Rates Along the Seattle Fault Zone Using Low Temperature Thermochronometry

The Seattle Fault Zone (SFZ) is a region of complex, east-west striking thrust faults in the Puget Sound area in Washington. Radiocarbon dating of landslides has determined that the SFZ most recently ruptured ~900-930 years ago. At this time, non-glacial sedimentary rocks from the Blakeley Formation (26-37 Ma) were uplifted up to 7 meters along the hanging wall of the fault. In this study, we use low temperature (U-Th)/He thermochronology to constrain the timing and slip of the main thrust of the Seattle Fault Zone. The dating technique is used on apatite crystals from samples of the Blakeley sandstone to develop a time-temperature cooling history as the rocks were uplifted and subsequently exhumed. The apatite (U-Th)/He thermochronometer records the date that the mineral passed through 70℃ closure temperature. Based on a 25℃/km geothermal gradient, this closure temperature represents the upper 2-3 km of the crust. The samples were collected from a transect along the hanging wall of the fault, from Alki Point, Seattle in the west to East Lake Sammamish, Issaquah in the east. All samples were collected between 0.5 and 1 m from the surface, and at similar elevations in order to account for different exhumation rates. The rate of uplift along the fault will be determined by the dates recorded by the apatite thermochronometers, where younger dates indicate more rapid rates. From this data, we will back out erosion rates in order to constrain the total fault movement.

Brita Horlings

Joel Jacobsen: Anthropogenic Influence on Reactive Chlorine in the Troposphere

Reactive halogens (Cl, Br, I) effect the oxidative capacity of the atmosphere as well as the lifetime of pollutants and greenhouse gases by serving as oxidants directly and indirectly through their impact on the atmospheric abundance of the hydroxyl radical and ozone. Sea-Salt is the largest source of reactive halogens in the troposphere. A global modeling study suggests that anthropogenic activities have increased the abundance of reactive halogens in the troposphere, primarily through an increase in ozone deposition to the ocean surface which reacts with iodide in sea water to release reactive iodine to the troposphere. However, many uncertainties exist in modeling reactive halogen chemistry. Here, we investigate the trends in reactive chlorine over the last 800 years using ice core records of sodium (Na+) and chloride (Cl-). Excess Cl has been found to increase after the beginning of the anthropogenic time period (1850 C.E.). This qualitatively supports modeling studies suggesting larger amounts of reactive Cl due to anthropogenic activities.

Bing Yu Lee: Understanding the Temporal Variation of Methane Seepage at Southern Hydrate Ridge (SHR) using Acoustics

Methane reservoirs are commonly found throughout the world’s oceans and the release of methane from seafloor reservoirs is thought to make up 5 to 10% of the global atmospheric methane. In fact, the greatest deep-sea mass extinction in the last 97 Myr during the Paleocene-Eocene Thermal Maximum (PETM) may have been caused by methane release from seep sites along the upper continental slope margin. Recently, methane reservoirs along this margin have been gaining attention due to their potential to accelerate current global warming. Changes in seafloor pressure and temperature could destabilize these seafloor deposits and cause methane bubble plume release into the ocean. At SHR, an extensively studied active seep site located ~ 90 km offshore Oregon, discontinuity in methane plume release was observed, but still not well understood. Hence, using Acoustic Doppler Current Profiler (ADCP) and pressure data archived by the Ocean Observatories Initiative (OOI) Cabled Array, we will be investigating the potential correlation between tides and the presence of methane plume at SHR. Our study detects methane plume structures based on the proxies of echo contrast caused by acoustic-bubble interaction. By analyzing the derived plume structures and their correlation with 226 tidal cycles, we expect a trend of plume release triggered by low tides. Our study will provide the first high-temporal-resolution analysis on the methane plume release at SHR using OOI acoustic data.

Joshua Lee: Buildup of Larges Scale Field Test for Asteroid Sampler

Our current research with the Kinematics and Impacts Lab at the University of Washington entails the design, buildup, and field testing of an asteroid sampling system. These field tests include the buildup of two stage closer rockets, which will be highlighted in this presentation. This asteroid sampler field testing helps characterize the sampling process of impacting an asteroid at high speeds- necessitating our rocket system be capable of stable, high speed flight, even at an inverted trajectory. The booster stage, or primary stage, of the system consists of a single large motor to allow the system to reach between 3000-4000 feet above the ground. The sustainer, or second stage, consists of eight smaller motors clustered around a central body tube, allowing the second stage to be hollow. Finally, a hollow point steel nose cone caps the sustainer. Inside the nose come assembly a sample dive is attached, designed to eject during impact. Field testing of this system occurred in December 2018, with preliminary results being compiled.

Alex Lowe: A project proposal: Ancient plant community and climate of the Pacific Northwest (USA) during the Middle Miocene Climatic Optimum

The MMCO occurred ~17–14 Ma, is one of Earth’s most recent transient warming events, and may constitute our best modern analog for a warm Earth. Currently, the response of regional vegetation and climate to the MMCO in the western U.S. remains enigmatic, as previous studies utilizing different paleobotanical records arrive at conflicting inferences. For example, phytolith records suggest an open-habitat grassland – woodland mosaic persisted in Idaho from ~23–15 Ma, characterized by arid to sub-arid climates. In contrast, macrofossil records from other Pacific Northwest localities suggest that broadleaved evergreen forests spread northward to ~45 °N, following warmer, wetter, and seasonally milder climates. Comparing reconstructions from different proxies involves several confounding factors that are difficult to disentangle, including age differences, regional-specific factors (e.g., topography), and what ecological information is captured by each paleobotanical record. This collaborative project will avoid such confounding comparison by integrating plant microfossils (i.e., pollen/spores and phytoliths) and macrofossils (e.g., leaves) from eighteen PNW fossil sites that represent before, during, and after the MMCO. Fossil information will be placed into a refined temporal framework by high precision radiometric dating of interbedded tuffs. Aspects of the ancient plant community ecology will be assessed including relative abundance, diversity, leaf life span, habitat openness, and spatial heterogeneity. Climatic estimates will be developed using leaf physiognomic methods and co-existence analysis, the latter which considers the overlapping climatic tolerances of the fossil’s nearest living relatives. All these data will be integrated to assess temporal and spatial patterns in PNW climatic and vegetational response across the MMCO, and to provide insights critical to predicting the long-term effects of current anthropogenic warming.

Zack McIntire: On the Hydrodynamics of Crystal Clustering

The formation of crystal clusters may influence the mechanical behaviour of magmas. However whether clusters form largely from physical contact in a mobile state during sedimentation and stirring, or require residence in a crystal mush is not well understood. We use discrete-element fluid dynamics numerical experiments to illuminate the potential for clustering from both sedimentation and open-system mixing in a model olivine basalt reservoir for three different initial solid volume fractions. Crystal clustering is quantified using both bulk measures of clustering such as the R index and Ripley's L(r) and g(r) functions and with a variable scale technique called Voronoi tessellations, which also provide orientation data. Probability density functions for the likelihood of crystal clustering under freely circulating conditions indicates that there is nearly an equal likelihood for clustering and non-clustered textures in natural examples. A crystal cargo in igneous rock suites exhibiting a dominance of crystal clusters may be largely sampling magmatic materials formed in a crystal mush.

Megan Mueller: Post-Collisional Evolution of Western Anatolia: Tectonostratigraphy of the Saricakaya Basin

Anatolia is a complex mosaic of terranes that collided from the late Cretaceous through the Paleogene. In western Anatolia, the most significant collision occurred between the Sakarya Zone of the Pontide terrane and the Tavsanli Zone of the Tauride-Anatolide Platform. At least 700 km convergence since 90 Ma was facilitated by the subduction zone(s), today marked by the >1700 km long Izmir-Ankara-Erzincan suture. Despite the large volume of work on the numerous Anatolian terranes and collisions, basic questions regarding the onset of subduction, number and polarity of subduction zones, timing of collision, style of post-collisional deformation, and development of topography and fold and thrust belts remain enigmatic. Here, we discuss early fold-and-thrust belt development of the western Anatolian orogeny through the stratigraphic and sedimentologic evolution of the Saricakaya Basin. This basin is a small, poorly-studied sedimentary basin between the Izmir-Ankara Erzincan suture zone and basement-involved Söğüt Thrust fault, and exposes a thick, Eocene sedimentary sequence thrusted by post-collisional orogenic build-up. New age constraints from zircon U-Pb dating of volcanic deposits, and new data from U-Pb detrital zircon geochronology and sedimentary facies reveal changes in provenance and depositional environments related to the post-collisional evolution of the suture zone. We show that the Saricakaya Basin is an Eocene post-collisional wedge-top basin created by loading from the Söğüt Thrust, and the depositional environments record periods of thrust building and quiescence. Unlike the thin-skinned fold-and-thrust belt of central Anatolia, the Saricakaya Basin documents an along-strike change in deformation style and orogenic evolution.

Haley Redinger: A Comparison of Growth Strategies by U-reducing Bacterium Shewanella putrefaciens CN32

Widespread distribution of dissolved uranium (U) from natural and anthropogenic sources poses a challenge to both environmental and human health. Some bacteria are known to reduce highly soluble U(VI) into more stable U(IV), limiting the rate it may leach into subsurface environments. Therefore, understanding how this metabolism functions in situ is vital for predicting subsurface U transport. Any thorough understanding of microbial metabolisms must compare different means of energy production (i.e. catabolic reactions). This means the metabolic processes involved in U(VI) reduction must be compared to those where an alternative terminal electron acceptor (TEA) is used. The facultative anaerobic bacterium Shewanella putrefaciens strain CN32 has the focus of many recent studies on U, but there has yet to be a detailed study of its metabolic efficiency across multiple TEA’s. This work quantitatively examined the metabolic efficiency of Shewanella putrefaciens CN32 by comparing the ratio of cells produced to the total mass of protein produced when growing on three different TEA’s: O2, Fe(III), and U(VI). Furthermore, the overall health of the culture was evaluated by measuring the size of cells grown with each TEA. Initial results indicate that both a larger average cell size and larger ratio of cells to protein mass correspond with potential Gibbs energy of each catabolic reaction (in decreasing order: O2, Fe(III), U(VI) reduction). Gaining a further understanding on bacterial U reduction will allow for hazard mitigation methods to be developed and used in at-risk areas around the world.

Nicole Sarieddine: Determining the month of soil carbonate formation for paleoclimate reconstruction

Carbon dioxide concentrations have been on the rise since preindustrial times due to anthropogenic emissions. Understanding how past climates have responded to changes in the atmosphere is important to understand how our current climate will react to changes in our present-day atmosphere. Soil carbonates record the temperature at the time of their formation in their stable isotopic composition (called clumped isotope geochemistry). Ancient soil carbonates can record the temperature and allow us to better understand paleoclimates. Understanding what time of year soil carbonates form allows us to better interpret the temperature being recorded. The timing of changes in soil moisture is likely one of the most important environmental factors to consider. We test whether soil carbonates form during soil drying events using soil moisture and temperature data measured remotely by a satellite called Soil Moisture Active Passive (SMAP). This satellite has been gathering near-surface soil moisture data globally since 2015 at 35-65 km resolution. We compare the air temperature of the month with the greatest net negative soil moisture content month (determined from the satellite data) to the measured growth temperature of soil carbonates (estimated through geochemistry). We first compare the month of drying of three locales in North America, then extend the analysis globally to all locations for which soil carbonate clumped isotope data exist. Preliminary results suggest that the temperature of the month with the most drying agrees with formation temperature we estimated from clumped isotope geochemistry within one degree for a site in Nebraska and within seven degrees for a site in Wyoming. These results suggest that soil drying promotes soil carbonate formation in some environments. By using soil carbonates to explain past climates, we will improve temperature change estimates, which will help improve climate models for the future.

Kelsay Stanton: Tectonic implications recorded by Pleistocene and older marine terraces above the Cascadia Subduction Zone, Willapa Bay, Washington

What is the record of subduction-related deformation at the timescale of a million years? Pleistocene and older marine terraces up to 400 feet above sea level near Willapa Bay, southwestern Washington may provide insight to the mechanism and timing of deformation above the Cascadia Subduction Zone. GIS analyses of terrace surfaces and detailed mapping will provide geological and structural information about terrace sets previously mapped as a single unit. Dating of terrace sediments will provide estimates of terrace ages and uplift rates. Comparison of terrace uplift rates around Willapa Bay can suggest a mechanism of uplift. If uplift of a given terrace is approximately the same north to south along the coast, I infer that most uplift has been from unrecovered elastic strain related to subduction. If the uplift of a given terrace is remarkably different north to south, faults and folds in the North American plate may be causing deformation.

Max VanArnam: Modeling Monsoon Flood Erosion in the Eastern Himalaya: using HEC-RAS to simulate velocity and depth for high discharge annual flows

When seeking to better understand specific bedrock river erosional processes due to flooding, numerical modeling can help answer many questions, specifically the extent to which floods contribute to setting the landscape. The eastern Himalaya experiences multiple flooding events of different magnitude: annual monsoon floods (10^3 m3/s) and centennial outburst floods (10^5 m3/s). This region also experienced at least two ancient megafloods during the Holocene (10^6 m3/s). Previous studies of flooding in the region have assessed the potential geomorphic role of the outburst floods and megafloods; however, the relative geomorphic impact of annual monsoon flooding remains unknown. To fully understand the relative erosive power of these eastern Himalayan floods, it is necessary to compare the hydraulics of outburst dam-break floods to the hydraulics of seasonal monsoon flow. To do this, we will use HEC-RAS to numerically simulate monsoon flood flow in this region. We can analyze patterns of flow velocity and depth (HEC-RAS outputs) to understand the spatial pattern of shear stress during monsoon floods. We expect to find that monsoon flow will yield lower magnitudes of shear stress and more homogeneous patterns of potential erosion compared to those observed for the outburst floods and megafloods. Understanding these erosional spatial patterns will help us better recognize the relative contributions of various magnitude floods and the extent to which each can set the landscape.

All Things Life (Astrobiology and Paleontology)

April 4th, 9-10:30am, JHN 170

Michael Kipp: Does the C/N ratio of organic matter in ancient marine sediments record dissolved oxygen levels?

Reconstructing dissolved oxygen levels in the ancient oceans is a fundamental task in paleoceanography. Accurate assessments of dissolved oxygen levels are critical for understanding early animal evolution, the evolution of major nutrient cycles, and even recent climatic fluctuations. Despite sustained interest in this topic, there are few good quantitative proxies for dissolved oxygen in the ancient ocean. Here I explore the idea that the ratio of carbon to nitrogen (C/N) in organic matter buried in ancient marine sediments can be used to reconstruct paleo-redox conditions in the overlying water column at the time of deposition. I first evaluate C/N trends across modern marine basins, and then use published databases of ancient marine sediments to explore C/N trends in various low-oxygen paleo-environments. These exercises show that in some instances C/N ratios follow coherent patterns both between and within geological units, with higher C/N ratios tending to occur in more strongly anoxic settings. However, several confounding factors must be carefully addressed before deriving quantitative paleo-redox reconstructions from these data. I outline a cautious way forward that involves end-member mixing models and cross-comparison with other established proxies, and speculate on the potential utility of this novel geochemical tracer.

Jana Meixnerova: Expanding our understanding of Archean life using transitional metal isotopes

Our understanding of the co-evolution of life and surface environments on the early Earth hinges on our ability to decipher and correctly interpret geochemical proxies from the ancient rock record. The analytical advances in mass spectrometry of the past two decades have allowed us to consider an increasing range of geochemical signals in much smaller quantities. Perhaps most notably, the development of high-precision MC-ICP-MS enabled the application of non-traditional stable metal isotopes to research in the Earth Sciences. In geochemistry, isotopes of metals such as redox-sensitive U, Mo, and Cr have since been extensively used to track the degree of oxygenation of the ancient water column and thus helped refine our grasp of Earth’s surface geochemistry in the deep time. Another avenue for metal isotope applications is tracing of life itself, as many important groups of organisms may impart during metabolism a specific isotopic fractionation on their metalloenzymes, which can then be recovered from their remains in sediments. We have explored this possibility in the case of methane cycling microbes, which are thought to have been a dominant form of life in the Archean Eon and to have significantly contributed to the atmospheric composition at that time. We separated organic matter from bulk rock and tracked its trend in Zn, Cu, and Ni isotopes across two Archean stratigraphic sections, the 2.7 Ga lacustrine Tumbiana and marine Hardey Formations. These lithologies have been previously characterized in detail using the established carbon and nitrogen isotopes, molybdenum isotopes, and iron speciation. Our data is the first organic matter-specific metal isotope dataset from a continuous stratigraphic section on record, and our results shed a new light on the life and environment on the early Earth, with the promise of new metal isotope biomarkers for methane cycling biota.

Lucas Fifer: Habitability implications of high CO2, CH4, and H2 gas concentrations in Enceladus’ ocean

Plumes erupting from cracks in the icy surface of Enceladus, a moon of Saturn, offer a glimpse into a subsurface ocean, which has pH, salinity, and temperature conditions that may be favorable for life. Measurements of the plume chemistry by Cassini are our sole window into the ocean composition; however, a major issue is that the plume will be highly fractionated from the source ocean as it erupts to the surface. To understand the ocean chemistry, we developed a numerical model that accounts for key fractionation processes that occur: (1) as gases exsolve from the ocean surface and (2) as water vapor condenses out of the plume. We modeled fractionation due to gas exsolution using a thin-film mass transfer model for water vapor (H2O), carbon dioxide (CO2), methane (CH4), argon (Ar), ammonia (NH3), and hydrogen (H2) from the surface ocean. Then, we estimated the water vapor loss via condensation as the plume erupts through ice fissures to the surface. Our results indicate that the ocean is highly enriched in gases in the order H2 = Ar = CH4 > CO2 ⨠ NH3 compared to the plume (after correcting for condensation) because different gas species erupt at much different rates. The high CO2 gas content we estimate would acidify the ocean and implies a lower pH compared to previous studies. Furthermore, microbial life could be fueled by high H2 and CH4 gas concentrations. Alternatively, the presence of concentrated H2 and CH4 gases could be evidence against life because microbes should have consumed them. We need a rigorous understanding of these and other fractionation processes to constrain the conditions of Enceladus’ formation, its long-term evolution, and the present-day composition and habitability of its ocean.

Hillary Smith: Environmental Controls on the Earliest Animal Ecosystems

During the Cambrian Period, 541 Ma to 485.4 Ma, the radiation of animals generated substantial diversity and produced most extant phyla. However, there remains a poor understanding of nutrient cycling during this exciting evolutionary interval. Furthermore, the point at which Earth’s oceans became fully oxygenated – and widely amenable to animal life – is unknown. It thus remains unclear whether oxygen exerted the primary control on the distribution of animals during their early evolution in the Cambrian. In order to elucidate the dynamic between oxygen and early animal ecosystems, we examined the Mt. Isa drill core from the Georgina Basin, Australia, which intersects the exceptionally well-preserved ~510 Ma Currant Bush Limestone. We used measurements of organic carbon (δ13Corg) and nitrogen (δ15N) isotope ratios as proxies for oxygen and nutrient cycling in ancient marine environments. The preliminary data suggest that at ~510 Ma, the Georgina Basin water column was predominantly anoxic. Nitrogen isotope ratios (δ15N from 0 to -1‰) are indicative of anaerobic N2-fixation-dominated ecosystems. Ratios of total organic carbon to total nitrogen (25 to 30) also suggest anaerobic organic matter remineralization, as smaller ratios would be expected in well-oxygenated waters. Both of these signals are consistent with low ocean oxygen levels. The organic carbon isotope ratios (δ13Corg) range from -30‰ to -31‰, consistent with carbon fixation by oxygenic photosynthesis, suggesting that oxygen production was insufficient to fully oxygenate seawater. Future work will explore whether these signs of anoxia correlate with organic biomarker proxies for eukaryotes, indicating animal abundance, from work done by our collaborators at Australian National University. Together, these data will clarify the ecology of this mid-Cambrian animal ecosystem.

Brody Hovatter: The early Paleogene rise of eutherians and decline of multituberculates and metatherians: Insights from analysis of dental disparity, morphospace occupation, and body size of earliest Torrejonian (To1) mammals from northeastern Montana, USA

The rise of eutherian mammals following the Cretaceous-Paleogene (K-Pg) mass extinction event is well documented. However, the timing and pattern of the changeover from more ancient lineages to the lineages leading to extant eutherian orders remains poorly resolved. The Tullock Formation in northeastern Montana provides an excellent window into a key time interval to address this gap. It preserves fossils from the first ~1.2 million years after the K-Pg (66.05–64.87 Ma), spanning the Puercan (Pu1 and Pu3) and earliest Torrejonian (To1) North American Land Mammal “ages.” Analyses of earliest Paleogene local faunal dynamics have shown that from Pu3 to To1 multituberculates and metatherians sharply declined in taxonomic diversity, while eutherians came to predominate. What changes in diet and body size accompanied this transition? And what do they indicate about changes in the ecological structure of these mammalian faunas? Here we report on patterns of dental disparity, morphospace occupation, and body size in the To1 mammalian fauna from northeastern Montana. We applied landmark-based geometric morphometrics to samples of multituberculate premolars and metatherian and eutherian molars, and estimated body mass using appropriate regression formulae. Our results indicate that relative to corresponding aspects of the Pu1 mammalian fauna (i) To1 metatherians had similar levels of dental disparity, occupied regions of the morphospace corresponding to mostly animal-based diets, and were on average similar in body mass, whereas (ii) To1 eutherians had greater dental disparity, occupied a greater amount of the morphospace corresponding to plant-based diets, and exhibited greater body size disparity. Taken together, our results suggest that taxonomic and ecological diversification of eutherian mammals was underway less than 1 Ma after the K-Pg boundary and was characterized by an expansion in feeding ecologies toward herbivory.

Paige Wilson: Seafood Salad: A Diverse Florule from the Late Cretaceous-age Hell Creek Formation of Montana

The Cretaceous-Paleogene (K/Pg) boundary marks a major mass extinction resulting in global faunal turnover, notably the extinction of non-avian dinosaurs. The Hell Creek Formation in northeastern Montana contains some of the most well-studied vertebrate localities recording this mass extinction, however, very little is known of the floral record in this area. As part of an effort to reconstruct floral changes across the K/Pg in northeastern Montana, this study presents a highly diverse flora from the Seafood Salad locality, located 65 m below the K/Pg boundary in the Hell Creek Formation, Garfield County, Montana. Leaves, stems, and reproductive structures (e.g., cones and seeds) are preserved in massive, bedded siltstones as compression fossils. Seafood Salad is significant in that it is represents a “pre-disaster” community before the end-Cretaceous mass extinction. It also constitutes a unique taphonomic setting with abundant bivalve and gastropod shells preserved along with plant material. We interpret the plants in these deposits as reflecting a local riparian community. Preliminary study indicates that the Seafood Salad flora was diverse and dominated by angiosperm trees, with abundant conifer specimens of a few taxa, along with rare ginkgoes and ferns. So far, we have described over 20 morphotypes and sought to establish their affinity to modern groups and to contemporaneous taxa found in Montana, North Dakota, and New Mexico. Many taxa are found in previously published, lower Hell Creek Fm floras as well as the Hell Creek floral zones of North Dakota, but there are significant differences in taxa and abundances between these assemblages indicating that the regional vegetation in the latest Cretaceous exhibited significant spatial and temporal heterogeneity.

Ice World Hoth (Glaciology)

April 4th, 10:45am-12pm, JHN 170

Ben Hills: Inferences from a subglacial lake at the South Pole constrain ice temperature and dynamics

Liquid water persists as a subglacial lake under ~3 kilometers of ice at the South Pole. Both airborne radar (Carter et al., 2007) and seismic reflections (Peters et al., 2008) have been used to independently confirm the existence of this lake. However, the thermodynamic setting and therefore the ultimate fate of this lake has been under debate. Some authors argue that the ice in this area is cold and that the lake is now freezing. Here, we use ground-based radar and GPS to constrain the extent and the dynamic setting in which the South Pole Lake exists. We observe that the lake area is approximately 35 km2, significantly smaller than previously stated. On the other hand, the radar data show a strong bed reflection in much of the area immediately surrounding the lake, indicating the possibility of a more extensive wet bed and likely melting. In conjunction with the field observations, we use a one-dimensional temperature model to assess the likelihood of melting/freezing at the ice-water interface. Contrasting previous hypotheses, we find that a temperate bed is realistic for the range of plausible geothermal flux and paleo accumulation rates at the South Pole.

Alex Huth: A comparison of ice fracture models

The essential roles that fracture processes play in the evolution of the Antarctic ice sheet are iceberg calving, which is responsible for roughly half of Antarctic ice mass loss, and weakening of ice shelves, which reduces their ability to restrain discharge of grounded ice into the ocean. Ice fracture is typically simulated using linear elastic fracture mechanics (LEFM), continuum damage mechanics (CDM), or zero stress models. Here, we overview how these approaches differ based on their assumptions of rheology and ice geometry. Then, we compare the performance of each approach to a 2D full-Stokes model where we represented crevasses explicitly. We ran the models with a variety of basal conditions and water depths within the crevasses, and tested the full-Stokes model with both nonlinear viscous and linear elastic rheology. Based on the results, we recommend a CDM approach for capturing fracture propagation over zero stress or LEFM models due to its time-dependence and applicability regardless of geometry or viscosity assumptions, but we also discuss potential advantages of combining approaches to parameterize damage for large-scale applications. We further support our recommendation for CDM over zero stress models by testing both approaches within our material point method (MPM) for large-scale ice flow/fracture, and we use the CDM approach to simulate the 2017 calving of iceberg A-68 on the Larsen C ice shelf.

Taryn Black: A multidecadal record of outlet glaciers in northwestern Greenland

Marine-terminating outlet glaciers of the Greenland Ice Sheet are in retreat, and their retreat has accelerated over the last two decades. Previous studies of a small number of glaciers or studies over several months or years have conventionally associated these changes with climate forcing. However, there is no published literature that looks at multi-decadal retreat trends and forcings on a regional scale and at regular time intervals. We have created a record of annual outlet glacier fronts since 1972 for 92 glaciers in northwestern Greenland in order to better assess the timing and magnitude of glacier retreat. These glacier fronts were mapped from a combination of optical and synthetic aperture radar satellite imagery. This record shows that nearly every glacier in the study region has retreated over the last several decades, with only one small glacier that has significantly advanced. Widespread regional retreat in northwest Greenland began in the late 1990s and has persisted to the present. Continuing work with this glacier front record will assess the relationship between the timing of glacier retreat and various forcing mechanisms, such as air temperatures, ocean temperatures, and sea ice characteristics.

John Christian: The Clydesdale and the Whippet: Idealized investigations of marine-terminating glacier dynamics

Many marine-terminating outlet glaciers have undergone grounding line retreat in recent decades, but their long-term responses to anthropogenic warming remain uncertain. One challenge is that these glaciers are sensitive to both atmospheric and ocean forcing, but the roles of these forcing types vary widely across glacier settings. Here, we apply a recently-developed idealized model to investigate outlet glacier response in a general framework. This model is derived by tracking the fluxes of accumulation, interior ice flow, and grounding-line discharge (i.e., discharge to the ocean). It resolves two fundamental timescales of outlet glacier response: a fast multidecadal grounding-zone adjustment, and a slow millennial adjustment of the large interior reservoir. These response times fundamentally govern the glacier’s response to climate forcing. However, the idealized model also shows that the temporal characteristics of the response also depend on the type of forcing. If the forcing is applied in the interior (i.e., surface mass balance perturbations), more of its high-frequency content is filtered out before it can be realized as glacier advance or retreat. Conversely, grounding-zone forcing (i.e., ocean forcing) can quickly drive advance or retreat, though the full glacier response still requires slow adjustment of the interior. This forcing dependence applies both to the glacier’s response to noise in the climate system, and to long-term, secular climate changes, and thus has implications for attributing observed glacier change, and understanding future changes committed by our current climate.

Trevor Hillebrand: West Antarctic Ice Sheet fluctuations during Pleistocene super-interglacials

We recently recovered bedrock from a depth of 150 m beneath the West Antarctic Ice Sheet (WAIS) at the Pirrit Hills to test for exposure during past interglacial periods. Cosmogenic nuclide and optically stimulated luminescence measurements on the rock core reveal that it has been buried by ice for the entire Pleistocene, and likely for much longer. Here, we use a 540-member ensemble of 3D ice sheet model runs to understand the persistence of ice cover in this region. We explore 90 parameter combinations, two model resolutions (40 km for the whole continent; 20 km for nested WAIS domain) and three Pleistocene super-interglacial periods (Marine Isotope Stages 5e, 11, and 31). We examine possible contributions from ice shelf hydrofracture and ice cliff failure mechanisms, as well as the effects of different rates of ice shelf melting, isostatic adjustment, and basal sliding. Future experiments will involve offline coupling with climate and ocean models, as well as exploration of the uncertainties in bed topography. As more subglacial data become available to determine if and when the WAIS has collapsed in the past, ice sheet modeling can help elucidate the climate thresholds and processes involved in large-scale deglaciation.

Afternoon Allochthons (Structure and Tectonics)

April 4th, 1:45-3pm, JHN 170

Jordan Wang: Evidence for Fault-Valve Behavior in Ultracataclasites of Carbonate-Hosted Normal Faults, Central Apennines, Italy.

Faults control the strength of the crust in-part by providing structural pathways for the release and redistribution of supra-hydrostatic fluid pressures over seismic cycles. Recent studies in the dynamics of fluid-fault interactions show how the spatial and temporal changes of fluid movement in fault zones is likely co-evolving with changes in fault zone deformation, but the exact behavior of these cyclical processes has been elusive due to the transience of fault fluids, fault zone permeability, and fault rock deformation features. To understand the interplay of these complex fluid-fault processes, it is important to determine the spatial and temporal contexts of fault materials using a combination of structural and geochemical evidence. I examine fault precipitates from three carbonate-hosted normal faults of the Central Apennines, Italy, to show how deformation features on the scales of centimeters to meters retain evidence for fault-valve behavior and possible co-seismic fluid flow along slip surfaces. 13C and 18O stable isotope measurements from materials across the fault zones indicate that precipitated calcite is distinct between the fault core and damage zone, suggesting compartmentalization of different fluid sources in different regions of the fault zone. By contrast, clumped isotope temperatures of ultracataclasites formed at the faults’ principal slip surfaces are the same as clumped-isotope temperatures of more distal vein materials in the damage zone, suggesting similar fluid sources. XRF and SEM chemical analyses of the fault materials resolve this discrepancy, showing that the ultracataclasites are made of highly comminuted, fluid-precipitate calcite of the same temperature as the isolated damage zone vein fluids. These findings support the formation of the ultracataclasites by fault-valve action, in which the deeply-derived damage zone fluids overpressured the faults, causing fluid expulsion and pressure drops along the slip surfaces, where fluid-precipitate calcite crystallized and was crushed during fault rupture.

Sarah Harbert: Exhumation and mountain building in the Marlborough Fault System, New Zealand

The Marlborough Fault System (MFS) is a complex suite of right-lateral faults at the boundary between the Australian and Pacific Plates on the South Island of New Zealand. It connects the Hikurangi Subduction Zone to the north with the dextral-reverse Alpine Fault to the south. The MFS is a broad zone of high relief, including several mountain ranges which are bound by strike-slip faults. We use low-temperature thermochronology – deriving the cooling histories of rocks as they approached the Earth’s surface - to constrain the history of exhumation and mountain building in the MFS over the last ~25 Ma. Previous thermochronology studies of the Inland and Seaward Kaikoura ranges, in the southeastern MFS, revealed two main phases of exhumation. The first, during the Oligocene to mid-Miocene, was focused in hanging walls of some of the MFS faults and reflects a period of thrusting when the MFS faults were oriented more parallel to the subduction zone. The second, starting after 5 Ma, was broadly regional and thought to reflect increasingly convergent relative plate motions. Structural and paleomagnetic studies support these conclusions, showing evidence for thrusting during the Miocene, followed by vertical-axis block rotations into orientations more favorable for strike-slip faulting rather than thrusting. However, all of these studies focused primarily on one corner of the MFS. Our apatite and zircon (U-Th/He) and apatite fission track thermochronology dataset provides cooling ages across nearly the entire MFS. We are able to extend the domain of Oligocene-mid-Miocene thrusting, as well as present variations in timing and amount of more recent exhumation.

Carolyn Nuyen: Crustal Deformation Near the Mendocino Triple Junction Inferred From GPS-Derived Strain Rate Maps

Crustal deformation in southernmost Cascadia represents the confluence of transpressive and convergent tectonics around the Mendocino Triple Junction (MTJ), which defines the intersection of the North American, Gorda, and Pacific plates. The transition between these major systems is achieved in part by faulting and deformation along the North American plate boundary, as well as large-scale rotation of the crust in southern Cascadia. However, the spatiotemporal history of deformation around the MTJ is poorly resolved due to previously sparse instrument coverage. Fortunately, GPS instrumentation in this area has increased significantly over the past decade, providing improved resolution on long enough time series to discern and refine steady strain rates. This work uses GPS data to investigate horizontal strain rates in southern Cascadia and how strain is accommodated through distributed and localized processes. To achieve this, we generate regional strain rate maps from horizontal GPS time series data collected over the past decade. We use multiple methods to clean the time series, including applying a monthly moving average, removing offsets from earthquakes and common mode signals, and employing a seasonal decomposition technique. We examine strain rate maps spanning from 2007-2017 to explore the heterogeneity of strain and its correlation with quaternary fault zones around the MTJ. Our results indicate that strain rates change across the MTJ from north to south, with compressional signals to the north and extensional signals to the south. We observe high maximum shear strain rates broadly across the San Andreas fault system, indicating that strain is distributed across multiple major fault strands. Lastly, we observe a band of high maximum shear strain rates north of the MTJ around the vicinity of the Mad River fault zone. We examine the interseismic slip rates in this region to gain insight into the seismic hazards associated with these faults.

Mattathias Needle: Reconstructing a folded surface: from point cloud to NURBS

Three-dimensional fold geometries can be interpolated from 2D exposures of folds or acquired from subsurface seismic data; but at the Bear Valley Strip Mine (Pennsylvania), there is a 3D exposure of a sandstone fold train comprised of the Whaleback Anticline and two adjacent anticlines. The Whaleback provides an opportunity to investigate the relationship of fold geometry to strain distribution as the walkability of the structure facilitates detailed observations of mesoscale expressions of strain on the fold’s surface. I generated a point cloud of the Bear Valley Strip Mine using Structure-from-Motion photogrammetry, but how do I develop a smooth and accurate surface geometry to relate fold geometry to the observable strain? Previous works on reconstructing fold geometries used km-scale map-derived data to develop a gridded surface and spectral analysis to remove noise. This technique is not ideal for the Whaleback because the exposed fold train is 102 m in scale and the Whaleback has an overturned limb, a geometry that is ignored by height-map raster data. An alternative to a raster grid would be generating a polygonal mesh; but meshing the point cloud would incorporate many of the small irregularities in the sandstone surface and produce non-physical interpolations across data gaps. Non-uniform rational basis splines (NURBS) are ubiquitous in computer-aided design to generate 3D surfaces comprised of a network of polynomial functions. Parameterizing a surface with NURBS can be accomplished over a variety of scales. NURBS can appropriately represent an overturned limb, as a single NURB-spline is a group of single-functions knotted together. Unlike mesh-generation, the orientation of NURBS are merely influenced by control points -- the control points act as “magnets” pulling on a spline. I applied NURBS to the point cloud and produced a smooth, continuous folded surface that spans the extent of the exposed sandstone. The NURBS interpolated plausible geometries for the fold train’s synclines where point-cloud data are lacking. Because the NURBS surface is a network of polynomial functions, the surface is mathematically operable within the language we use to describe fold form.

Ginevra Moore: Shallow offshore deformation in the Seattle fault zone

The Seattle fault zone (SFZ) is an east-west striking, north-vergent thrust fault system that is located beneath the greater Seattle area. In A.D. 900-930, a M 7.0-7.5 earthquake ruptured a blind, south dipping thrust fault in the SFZ. The event caused surface folding that produced up to 8 meters of land level changes, a local tsunami, and probable concurrent surface rupture on north dipping back-thrusts in the SFZ hanging wall. Over the last few decades, kilometer-scale geophysical datasets, lidar topography, and paleoseismology studies have been used to constrain the onshore SFZ geometry. From these observations, several regional structural models have been developed to explain the connectivity and kinematics of the SFZ at depth. However, current models lack information from offshore studies of the shallow subsurface. In 2017, a high-resolution seismic reflection dataset of the SFZ was acquired in the Puget Sound and Lake Washington. The dataset consists of multichannel reflection profiles from boomer and sparker sources with collocated chirp imagery. Here, we present interpretations of this new multi-resolution seismic dataset, resolving lithologic discontinuities in the upper 300 meters of the subsurface. We integrate our offshore seismic interpretations with a geomorphic analysis of both new and existing bathymetric datasets, along with published observations of shoreline elevation changes associated with the A.D. 900-930 event. We find: 1) evidence that onshore scarps continue in offshore seismic sections, 2) shallow deformation features that coincide with the near-surface locations of previously identified crustal scale structures, and 3) expressions of folding and vertical displacement of inferred Quaternary and Oligocene deposits, providing a strategy to assess the relative timing of deformation on the SFZ.

Shake, Rattle, and Roll (Seismology)

April 5th, 9-10:15am, JHN 170

Ian Stone: Topographic response to ground motion from modeled Seattle Fault earthquakes

Topography significantly amplifies earthquake ground motion under special conditions, but is rarely considered during seismic hazard analysis. In this project, we attempt to model the response of surface topography to scenario Seattle Fault earthquakes using 3D spectral element method modeling. A topographic surface and mesh with 30-meter resolution allow us to model site response in and around the city of Seattle up to ~3Hz. Using 3D velocity and attenuation models cognizant of local basin structure and shallow geology, we simulate a variety of scenario Seattle Fault earthquakes and compare the results with and without topography. We demonstrate that shaking is primarily affected on topographic highs and slopes, where we see locally amplified ground motion. Cliff faces adjacent to the Puget Sound show a consistently elevated and localized pattern of amplification. Topographic effects at a given site are highly dependent on topography shape, ground motion frequency and source location. Our findings could have significant implications regarding landslide hazard and hill-slope engineering in the city.

Kelley Hall: Induced Stresses on the Cascadia Megathrust during ETS Events and Implications for the Triggering of Tremor

We explore how fault stress evolves on the Cascadia megathrust during an episodic tremor and slow slip (ETS) event and compare the stress change to the spatial evolution of tremor. In order to explore spatio-temporal relationships between tremor and slow slip, we used displacement time series from ~50 GPS stations together with PNSN tremor locations to image the propagation of slip for two large ETSs in Northern Cascadia in 2010 and 2012. The Extended Network Inversion Filter (Segall and Matthews, 1997) is used to solve for the time-dependent fault slip. Our results for the 2010 event yield a Mw 6.8 event that began near Seattle on August 8th and propagated mainly to the north with some smaller slip to the south, similar to the tremor propagation pattern, and consistent with our static inversion results in Hall et al. (2018). To evaluate the effect of propagation direction on ETS, we analyzed the 2012 ETS, which initiated on Vancouver Island on August 25th and propagated southward yielding a Mw 6.8 event. For both events, the slip-pulse nature of the ETS process is clearly imaged by the inversion, with some fault patches continuing to slip for several days after tremor has passed through, but not for the entire duration of the event. Notably, we observe small amounts of tremor occurring ahead of the slipping region, and we found that this observation is independent of the along-strike propagation direction. We perform sensitivity tests using synthetic data to evaluate whether the spatial-temporal shift in the tremor and fault slip is resolvable given the necessary smoothing of the inversion. To explore the stress state, we used Poly3D to calculate the distributed stress change on the fault given the time-dependent slip distribution for each event, and compared these results to the tremor locations. We infer that the tremor must be sensitive to kPa of stress, as has been demonstrated in studies of tidally-triggered tremor (Houston, 2015; Hawthorne, 2010). We hypothesize that the initial bursts of tremor are triggered by the small leading stresses ahead of the propagating slip pulse.

Mika Thompson: Investigating the Performance of Earthquake Early Warning Algorithms on the Cascadia Subduction Zone

Earthquake early warning (EEW) algorithms use the first few seconds of an ongoing earthquake to rapidly predict when and where strong ground shaking is expected. The usefulness of an EEW alert depends on the accuracy of ground motion predictions and whether the alert provides enough warning to take mitigating actions. The low level of background seismicity at the Cascadia subduction zone (CSZ) makes it difficult to test EEW algorithms. However, we can assess the expected performance of point-source and finite-source EEW algorithms for events on the CSZ with a global dataset of local recordings of subduction zone earthquakes and a suite of thirty 3-D ground motion simulations of M9 Cascadia megathrust rupture scenarios. By re-arranging seismic stations to mimic the station density and source-to-site distances in the Pacific Northwest, we test the accuracy and timeliness of EEW algorithms in Cascadia and estimate expected warning times.

Ariane Ducellier: A two-year long catalog of low-frequency earthquakes for Northern California

Low-frequency earthquakes (LFEs) are small magnitude earthquakes, with typical magnitude less than 2, and reduced amplitudes at frequencies greater than 10 Hz relative to ordinary small earthquakes. Their occurrence is often associated with tectonic tremor and slow slip events along the plate boundary in subduction zones and occasionally transform fault zones. They are usually grouped into families of events, with all the earthquakes of a given family originating from the same small patch on the plate interface, and recurring more or less episodically in a bursty manner. They can be identified by looking for waveforms repeating simultaneously at several seismic stations. When enough (a few hundred) low-frequency earthquakes have been identified for a given family, a template waveform can be obtained by stacking all the waveforms corresponding to all the low-frequency earthquakes identified. Once a template is available, additional low-frequency earthquakes can be found by cross-correlating seismic data with the template, and assuming that a low-frequency earthquake is occurring whenever the value of the cross-correlation is higher than a chosen threshold. In this study, we use the templates obtained by Plourde et al. (2015) using data recorded by the FAME (EarthScope Flexible Array Mendocino Experiment) network in Northern California during an episode of high tremor activity in April 2008, and we extend their catalog to the whole two years (2007-2009) during which the seismic stations were installed.

Emma Myers: Downward Continuation Streamer Tomography: Exploring Shallow Plate Bending Faulting and Hydration

Plate bending faults are a common incoming slab feature to subduction zones, but their ability to act as a means for crustal or upper mantle hydration greatly vary. Imaging the velocity variations typical for plate hydration as well as discrete subsurface fault structures requires both crustal scale and fine, shallow geophysical methods. Streamer tomography with a long-offset streamer benefits from the short shot spacing used in active source surveys recorded on hundreds of receivers to provide both deeper penetrating refraction arrivals as well as dense horizontal ray coverage. However, deep water and/or low velocity material can result in near-offset refractions being overprinted by seafloor reflection arrivals for a significant portion of each shot gather. Downward continuation, a method for redefining the datum used in streamer tomography from essentially the sea surface to just above the seafloor, allows for suppression of the seafloor reflection and increased near-offset first arrival refractions for the shallowest turning rays. I propose that the 12.5 km long streamer data collected during the 2016 PICTURES (Pisagua-Iquique Crustal Tomography to Understand the Region of the Earthquake Source) experiment over a transect of the subducting Iquique Ridge along the Peru-Chile Trench with water depths of 3-8 km provides an optimal dataset for implementing downward continuation streamer tomography to characterize this portion of the incoming Nazca plate. This method of high-resolution shallow imaging of the upper most couple kilometers of the incoming plate can improve our understanding of decreased crustal velocities and their correlation to bathymetric and reflection imaged faulting. The distribution in depth and along-axis of plate bending faults and associated seismic velocity variations can provide insight to the hydration state of the incoming plate, which may subsequently influence seismicity at depth along the megathrust in this region.

The Final Frontier (Space and Planetary Science)

April 5th, 10:30-11:15am, JHN 170

Todd Anderson: Monitoring radio wave attenuation in the Earth-ionosphere waveguide with the World Wide Lightning Location Network

Solar events and Sun-magnetosphere interactions can cause significant impacts on Earth’s ionosphere. Solar flares and Earth-impacting coronal mass ejections enhance ionization in the lower ionosphere, inhibiting radio wave propagation in the Earth-ionosphere waveguide (EIWG). This enhanced ionization is observed in specific locations by ionosondes, and VLF radio wave propagation studies have previously been performed to assess the impact of space weather on the EIWG. However, these studies are typically limited by small numbers of fixed VLF transmitters and receivers, e.g. MSK stations, and as such can only observe the region of the EIWG along the few propagation paths between transmitters and receivers. Here, we use global lightning as a VLF source, and an existing lightning detection network as a receiver. The World Wide Lightning Detection Network (WWLLN) uses ~100 stations around the world to detect VLF sferics and locate associated lightning strokes. By mapping sferic propagation paths between lightning strokes and WWLLN stations, and considering how this distribution of paths changes during solar events, we can observe attenuation regions in the EIWG caused by space weather. By comparing these to existing global attenuation estimates (e.g. from the NOAA D-Region Absorption Prediction model) and ionograms, we can build a near-real-time monitor of the lower ionosphere with global coverage.

Ping-Chun Lin: Investigating wetted slope streaks in the McMurdo Dry Valleys, Antarctica: Do similar flows form on Mars?

Seasonal dark streaks on Mars known as Recurring Slope Lineae (RSL) propagate down steep, warm slopes and appear to be liquid water flows. However, the mechanism behind RSL formation is controversial, and both dry granular flow and percolating water hypotheses have been proposed. To determine if liquid water is responsible for RSL formation, I investigated similar dark streaks generated by percolating water in the McMurdo Dry Valleys (MDV) of Antarctica, an extremely cold and dry Mars analog site. The goal of this research is to identify the source of water to the MDV streaks, and to compare the MDV streaks to Martian RSL. I characterized the MDV streaks by (1) analyzing a ~30-day time-lapse video of the streaks collected on site, (2) investigating the drainage hydrology with a Digital Elevation Model, and (3) comparing hundreds of satellite images of the streaks from 2003-2017. My results show that the MDV streaks are very different from Martian RSL, which indicates that liquid water is not involved in RSL formation. Unlike Martian RSL, I found out that MDV streaks propagate downslope at much slower rates compared to Martian RSL, and do not grow and retreat seasonally. In addition, MDV streaks have distinctive patterns that are not apparent in Martian RSLs, and rapidly darken/lighten in response to relative humidity changes. Finally, MDV streaks form in response to extremely warm summer temperatures, conditions which are unlikely to prevail on Mars. These results are important for understanding how and if liquid water occurs on Mars’ surface.

Sarah King: New evidence that seasonal flows on Mars are dry, windblown sand avalanches

Recurring slope lineae (RSL) observed on Mars appear to be flows of liquid water because they seasonally propagate down sunny slopes in the spring and fade during the winter. Liquid water suggests the potential for life on Mars’ surface and has implications for future exploration; however, recent hypotheses contend that RSL form via dry sand avalanches. To test wet vs. dry flow hypotheses, we analyzed images and topographic data from Garni crater taken by the High Resolution Imaging Science Experiment (HiRISE) during the Martian summer and winter. Our results show that RSL size correlates with areas where we expect high windblown sand deposition, such as on the SE lee side of the crater, or in small gullies below large headwalls. Additionally, RSL do not appear on the wind-scoured NW side of the crater. These surface relationships indicate that RSL in Garni crater form via a dry process in which windblown sand is deposited by prevailing NE winds and seasonally avalanches down steep slopes. To further test our conclusions, we are examining additional confirmed RSL sites on Mars to see if they display the same behavior.

Andrew Shumway: The formation of low temperature perchlorate brines in Martian soils

Water is critical for life as we know it, but liquid water is only possible on Mars today as thin films adsorbed onto soils or as salt solutions because of cold and dry conditions. Salts and soils allow liquid water to form by lowering the freezing point, reducing the evaporation rate, and absorbing water vapor from the atmosphere. Although the stability of water-salt (brines) and water-soil mixtures are well-known on Mars, the stability of realistic soil-brine mixtures are practically unexplored. To address this knowledge gap, I studied the formation of perchlorate brines in simulated Martian soil at 25°C by measuring water activity – which indicates the amount of water available to chemical and biological processes. Perchlorates in particular merit this investigation because they have been detected in Martian soil and are believed to have the greatest ability to form brine under Martian surface conditions. To measure the stability of adsorbed perchlorate brines, I analyzed soil-brine samples at temperatures as low as -150°C with a differential scanning calorimeter, which identifies phase transitions by measuring changes in a sample’s heat flux. I find that adsorption onto soils greatly suppresses the temperature of ice and salt formation compared to pure brines. This indicates water is far more stable in soil-brine mixtures than in pure brines at realistic Martian concentrations, and that liquid water could form at much colder and drier conditions than previously thought. Under dry Mars-like conditions (relative humidity <50%) I find that adsorbed perchlorate brine is so stable that it does not freeze, and instead remains liquid down to -150°C. Water in adsorbed brines would be available to potential microbes, but the water activity I measure would be extremely challenging for life.

Some Like It Hot (Geochemistry)

April 5th, 1-3:00pm, JHN 170

Tianyi Huang: Heterogeneous potassium isotopic composition of the upper continental crust

Assessing the potassium isotopic composition of the upper continental crust is important for: (1) understanding the processes by which the crust is generated and modified; (2) constraining the K isotopic budget of silicate Earth. High-precision K isotopic data are measured for 70 well-characterized individual and composite samples from the upper continental crust, with a wide variety of petrology including diorite, granodiorite, granite, loess, shale, graywacke, pelite, and tillite, to constrain the K isotopic composition of the upper continental crust. δ41K varies significantly in I-type and S-type granites from Australia, A-type granites and granitoid composites from China, mainly reflecting influences from source heterogeneity. The post-Archean Australia shales (PAAS) and sedimentary composites from China have heterogeneous K isotopic compositions, while loess samples from around the world display limited K isotopic variation. δ41K values display a larger dispersion in shales than loess, with more intense weathering and higher chemical index of alteration (CIA). In addition, K isotopic compositions of most sedimentary samples are similar to or lighter than oceanic basalts. These observations suggest that chemical weathering significantly fractionates K isotopes. To summarize, the upper continental crust has a heterogeneous K isotopic composition, ranging from -0.68 to -0.12‰ with the average of -0.44 ± 0.19‰ (95% c.i., n = 70), which may be dominantly produced by K isotope fractionation during low-temperature water-rock interactions.

Yan Hu: Potassium isotopic heterogeneity in subducting oceanic slabs and implications for global K cycle

A key control on terrestrial potassium (K) cycling occurs through the subduction of K-rich marine sediments and altered oceanic crust (AOC). This paper reveals that a preference for the light K isotope during seafloor alteration and authigenic clay formation explains the enrichment of heavy K isotope in seawater relative to its riverine input and the bulk silicate Earth. Using the latest analytical techniques, we find a remarkable isotopic variability in the two major marine K sinks, with δ41K values ranging from −1.29 to −0.018‰ in drill core subducting sediments worldwide and from −0.593 to −0.049‰ across the oldest AOC in western Pacific. The primary control on δ41K variability in sediments is the abundance of clay minerals, either being inherited from weathering or formed in situ during diagenetic alteration, both of which typically favor isotopically light K except when K is being incorporated in its hydrated form. In comparison to the sediments, the bulk AOC (−0.327‰) underwent a net gain in isotopically heavy K relative to fresh basalts, despite its preferential uptake of light K isotope from seawater. Given such a previously unrecognized heterogeneous K isotopic composition, subduction of oceanic slabs has a profound influence on the K isotopic evolution of the continental crust and the mantle. Furthermore, these results show the promise of K isotope geochemistry in tracing subduction recycling of K, and its potential for distinguishing crustal inputs from subducted sediments (low δ41K) and AOC (high δ41K).

Addien Wray: Geochemical effects on the adsorption of uranium onto Shewanella putrefaciens CN32

The adsorption of chemical species onto charged surfaces is critical in regulating their transport in the environment. Notably, bacterial cell walls have negatively charged functional groups known to adsorb a variety of metals. Recent work has focused on the adsorption of radionuclides onto bacterial surfaces, given the widespread distribution of radionuclides from both anthropogenic and natural sources. Uranium has been of particular interest given its high potential for mobility under oxidizing conditions, where the soluble U(VI) is the dominant oxidation state. U(VI) is found primarily as complexation products of the uranyl ion, UO2(2+), as governed by in situ geochemical conditions. Importantly, the ability of those uranyl species to adsorb onto bacterial surfaces is varied. Therefore, the adsorption of U(VI) onto bacterial surfaces depends on geochemical variables such as pH, the co-presence of other cations, and ionic strength. We investigated the adsorption of U(VI) onto the gram-negative bacterium Shewanella putrefaciens strain CN32. This was done from pH 3-10, both with only U(VI) and with U(VI), Ca(II), and Mn(IV) co-present. These experiments were repeated over a range of ionic strengths, from 0.01 M to 0.5 M. Results demonstrate a monomodal relationship between U(VI) adsorption and pH, with a peak in the circumneutral range. As expected, ionic strength positively correlated with adsorption, independent of pH. Experiments with a co-presence of Ca(II) and Mn(IV) have yet to be completed, but we expect a uniform decrease in U(VI) adsorption with increasing concentration of those cations.

Nicolas Wogan: The Chemical Disequilibrium of Non-Photosynthetic Worlds

Krissansen-Totton et al. 2016 calculated the chemical disequilibrium of the atmosphere-ocean system on several planets and moons in our solar system. They found that Earth atmosphere-ocean system has significantly more available Gibbs energy (or chemical disequilibrium) than any other planet. This disequilibrium is maintained by life; most significantly by oxygenic photosynthesis. They propose high atmosphere-ocean chemical disequilibrium as a possible biosignature for exoplanets similar to the modern earth – planets with large photosynthetic biospheres. While a chemical disequilibrium metric seems to be a promising method for detecting life on photosynthetic worlds like our own, it remains to be determined how this metric applies to purely chemosynthetic worlds. We use two approaches for exploring the chemical disequilibrium of non-photosynthetic environments. The first approach is mostly completed, while we can only offer preliminary results for the second approach. First, we investigate the chemical disequilibrium of a modern chemosynthetic ecosystem – Antarctic Subglacial Lake Whillans (SLW). We perform two Gibbs energy calculations: one of the observed “living” SLW, and another of a modeled “dead” SLW. The “dead” SLW has a modeled steady-state chemistry such that there is not life influencing chemical cycling in the lake. We find that modeled “dead” SLW has more available Gibbs energy than the observed “dead” SLW. This result indicates that for purely chemosynthetic environments, anomalous chemical equilibrium is indicative of life. We also use photochemical-ecosystem models to determine plausible atmosphere-ocean chemical disequilibrium for Earth dominated by four different ecosystems: (1) no ecosystem (before the origin of life), (2) CO consumption only, (3) CO consumption and methanogenesis, and (4) CO consumption, methanogenesis and anoxygenic photosynthesis. These calculations, when completed, will more directly evaluate the chemical disequilibrium biosignature metric on purely chemosynthetic worlds.

Break 2:00 - 2:15pm

Joel Gombiner: Ice age flooding of Moses Coulee, eastern Washington

Pleistocene glacial flooding from the southern margin of the Cordilleran Ice Sheet formed the Channeled Scabland canyon system. Moses Coulee is one of the largest canyons, but unlike other Scabland canyons, Moses Coulee lacks connectivity to the Columbia River. Is the connection between the Columbia River and Moses Coulee buried by sediment (Bretz et al., 1956), eroded by glaciation (Bretz, 1959), very subtle (Hanson, 1970), or was the water source actually subglacial water from the Okanogan Lobe (Lesemann and Brennand, 2009)? This talk will discuss the source of Moses Coulee floodwaters using field observations, geochronology, and sediment provenance.

Mary Alice Benson: Sediment accumulation in a manipulated bay of Puget Sound, Bellingham, Wa.

Mud Bay, located in Bellingham, Washington, is infilling at a rate greater than expected sea-level rise. This study will quantitatively determine the degree of bay infilling. In 2013, based on qualitative studies, the City of Bellingham identified the pocket estuary of Mud Bay as a 10-year restoration priority due to degradation of habitat from sediment accumulation. Mud bay is an important habitat for eelgrass, shellfish and birds. Chuckanut creek, the primary fluvial input into the bay, has historically been a steelhead spawning ground. Anthropogenic factors that could have increased sediment input include logging, mining and quarrying in proximal areas. A rip-rap train trestle, constructed across the mouth of the bay, limits energy from tides, waves, and storm surge. During the construction of Interstate 5 additional sediment could have been transported to the bay by Chuckanut Creek. To determine the degree of bay infilling, cores were collected from four sites in the intertidal zone of the study area, near the mouth of Chuckanut Creek. Using 210Pb geochronology, sediment-accumulation rates were measured as 0.2 to 1.07 cm yr-1, with spatial variations attributed to differences in tidal currents and fluvial supply at each coring location. Accumulation rates were corroborated using 137Cs at one coring site. Both geochronological analyses established sediment-accumulation rates of ~0.8 cm yr-1 at this location. Sedimentary structure was examined using X-radiographs, and grain-size distributions were incrementally conducted for each coring site using a Beckman Coulter LS 13-320 laser diffraction particle-size analyzer. Relative sea-level rise projections for the next century for this location are ~30 cm, with a probability of exceedance of 95%. Accommodation is decreasing because rates of infilling exceed that of local sea-level rise. Additional work is needed to determine what fraction of the observed infilling is attributed to anthropogenic stressors, instead of natural causes.

Julia Kelson: Seasonality of soil carbonate accumulation: insights from a synthesis of modern-Holocene clumped isotope data and numerical modeling

The ability to reconstruct ancient climates on land is critical for investigating the evolution of habitats, ecology, climate, tectonics, and landforms. Soil carbonates are an important archive of terrestrial paleoclimate because they are ubiquitous in the geologic record. However, we currently lack a process-based understanding of what time of year soil carbonates form. Seasonal variations in temperature are generally larger than the secular or spatial changes in temperature that we are interested in quantifying, thus, it is critical that we understand the seasonal bias of paleosol carbonate formation. To address this problem, we first compare growth temperatures of modern soil carbonates estimate through clumped isotope thermometry to monitored local temperatures. We find that most carbonates have a warm season bias, but the magnitude of this bias varies from 1-20 °C. Next, we use a 1D numerical model (HYDRUS) of soil physics and chemistry to explore factors that could control the seasonal bias. We simulate the transport of water, heat, and solutes in soils to test the hypothesis that the timing of soil carbonate growth is sensitive to changes in soil moisture. Preliminary model simulations show that soil carbonate formation occurs throughout the year, but that most carbonate accumulation occurs after large rain events when soil carbonates dissolve and reprecipitate deeper in the soil column. Through this modeling effort, we seek to build a process-based understanding for soil carbonate formation. We will identify which environmental factors are most important and which can be identified from paleosols for use in reconstructing paleoclimates.

Quick, Quick, Do Tell Me! (Up-Goer 5)

April 5th, 3:15-4pm, JHN 170

Lindsey Davidge: Learning about the old sky by using a light box to find middle-big waters in ice sticks

At the top and bottom of the world where it is very very cold, water and ice fall from the sky and stay on the ground for a long time. Sometimes we get very long sticks of ice out of the ground that have cold ice from many tens of hundred hundred years ago, and the things in the cold ice tell us about the sky tens of hundred hundred years ago. We learn more about the old sky when we find new things in the ice sticks. We usually find different kinds of air and different kinds of water from the old sky. The number of big waters tells us about how hot or cold the sky was. There are also less big waters that are still bigger than normal waters, but there aren't very many of them so they are harder to find. Finding the middle-big waters in the ice sticks will tell us new stuff about how wet or dry the old sky was. A new light box makes it easier to find the middle-big waters, but to find the middle-big waters in the ice sticks we first need to make them more like air. We use a hot box and some other things to get the ice sticks ready for the light box to find the middle-big waters. Our light box finds normal waters, middle-big waters, and big waters, but right now it only finds different kinds of waters in normal water. Soon, this light box will be able to find the middle-big waters in real ice sticks so that we can learn more about the old sky.

Virginia Littell: High, low, heavy, light - using these things to tell us about how and when places that are high today got so tall

Some people who study this ball we live on really want to know about how, when and why the highest places on this ball got so high. One place many people study to answer these questions is the dry, huge, tall area across the big water from where we live in the direction that the sun sets. There are a couple ways to figure out how tall this high place was before now, but the one this study focuses on uses rain. We can use rain to know how tall a place was by using the fact that how heavy or light the water is in the rain is controlled by how short or tall a place is. If we have numbers for these things today at our huge, tall area, and a way to know how heavy the rain was before, we can use both to figure out how high the same place was when the older rain fell. However, there is one big problem that people have not tried to figure out yet that could change our understanding of the timing of how high the huge, tall area was before today. This study will show how rocks from low areas near the huge, tall area can better both our understanding of very old rain in the area and our answers to when the huge, tall place got so tall. It is important for people who study things like the rocks, remains of animals or green sun-loving things, and/or old rain/winds of this area to know what it was like in the past because it does away with some not-known things that could change what we learn from their studies.

Tristan Bench: Assessing Surface Erosion Rates of Rocks in the Context of Petroglyph Preservation Analyses using Cosmogenic Isotopes

Petroglyphs are human-made images created by the anthropogenic removal of material on a rock surface. The images are often subjected to various natural and anthropogenic conditions that cause them to degrade over time and eventually disappear. The ability to quantify surface erosion rates and assess the environmental effects on petroglyph surfaces is crucial for planning preservation strategies. An effective method to assess surface erosion rates is measuring the buildup of cosmogenic nuclide 10Be in rock surfaces over time. Natural high- energy cosmic rays striking rock surfaces will convert 16O to 10Be in silicic minerals, which will accumulate as a function of time and surface shielding, thereby allowing the isotope to be used as a chronometer for surface exposure and erosion. Bulk samples taken from Bighorn Basin, Wyoming, Valley of Fire, Nevada, and San Juan River Corridor near Sand Island, Utah, will be prepared for 10Be analysis using Accelerator Mass Spectrometry to establish erosion rates of rock surfaces. No samples directly from petroglyph surfaces will be taken; surfaces in environmental proximity to the petroglyphs are just as effective for analysis and will be obtained for study. Acquiring quantitative erosion data using this method provides a better understanding of the erosive history of petroglyph surfaces and can help identify unique environmental and historical implications to erosion, such as erosion episodicity (whether spallated, gradual, etc.) via applied modelling techniques. This knowledge may offer needed data for communities and parks wanting to optimize the preservation of their material heritage.

Marina Duetsch: The over filling of air with water and how it controls water same places

Water same places can help us learn about the world's ring of water from when it comes out of the land or big and deep water to when it builds soft white things in the sky that make rain. This is because they change their number when water goes from one form to another. So the number of same places in water tells us something about what happens in the water ring. One important part of the water ring that controls the number of same places is where water becomes sky ice. This usually happens where the air is over filled with water, and the over filling of the air is important for the number of same places in the ice that eventually falls down from the sky. Many computers don't have over filling of air, that's why the same places part uses a line instead, which gets bigger when the air gets colder, but this is probably not what happens in real life. Only a rather new computer uses the actual over filling of air. Here we use this new computer to see if the line that the old computers used makes sense, and how this controls water same places in ground ice. The answer is that the over filling of air is more than just a line, but the number of same places can still be explained quite well by a line, especially if the line is not straight.