Geological Sciences Theses and Dissertations

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Open Access
A Biogeochemical Study of Groundwater Arsenic Contamination in the Southern Willamette Basin, Oregon, USA
(University of Oregon, 2016-11-21) Maguffin, Scott; Jin, Qusheng
The mobilization and transformation of arsenic within the critical zone is a major cause of human suffering worldwide. Microorganisms, as they grow and utilize organic matter, accelerate redox processes that can transform and mobilize arsenic within aquifers on a large scale. As such, naturally occurring groundwater arsenic is a particularly hazardous problem that is chronically poisoning over 100 million people annually. Historically, groundwater arsenic research has been focused on the two principal inorganic arsenic species: arsenate [As(V)] and arsenite [As(III)]. Recently, organic arsenic species have garnered more attention due to their mobility, toxicity, and contemporary recognition of the ephemeral yet significant role they have in the global arsenic cycle. Here, I discuss laboratory and in situ experiments focused on exploring how microorganisms transform, mobilize, and sequester arsenic within a biogeochemically complex aquifer system. In my laboratory experiments, I collected aquifer sediments from a naturally contaminated bedrock aquifer and incubated a series of laboratory microcosms. Our results show that simultaneously robust iron and sulfate reduction temporarily mitigated arsenic contamination but then directed arsenic to an unstable adsorbed phase were it was later mobilized. Second, I discuss two aquifer injection experiments designed to examine in situ microbial redox processes and the further explore the potential to stimulate arsenic sequestration through arsenic-sulfide precipitation. Our results show that in situ stimulation of microbial metabolisms accelerated the reduction of arsenic bearing iron (oxy)hydroxides as well as sulfate and arsenic reduction. Within 3 weeks of these contemporaneously occurring redox reactions, 90% of the dissolved inorganic arsenic was removed (~2000 ppb) and an effective long-term, anaerobically stable, sequestration of arsenic was observed by way of a significant increase of arsenic-sulfide precipitate. Finally, using both the laboratory and field experiments, I explore the potential of organic arsenic production rates under stimulated conditions. We report new methylation rates that are consequential to the potential efficacy of enhanced, biologically-driven arsenic remediation and the reconsidered significance of biomethylation pathways in aquifers. These results expand our current understanding of the metabolic reach aquifer microorganisms potentially have over the fate of arsenic.
Open Access
A Genus-level Phylogenetic Analysis of Antilocapridae and implications for the evolution of headgear morphology and paleoecology
(University of Oregon, 2020-02-27) Flora, Holley; Davis, Edward
The shapes of artiodactyl headgear play key roles in interactions with their environment and each other. Consequently, headgear morphology can be used to predict behavior. For example, larger, recurved horns are typical of gregarious, large-bodied animals fighting for mates. Smaller spike-like horns are more characteristic of small-bodied, paired mates from closed environments. Here, I report a genus-level cladistic analysis of the extinct family, Antilocapridae, testing prior hypotheses of evolutionary history and headgear evolution. I included 53 post-cranial, cranial, and headgear characters, expanding on previous analyses by developing 14 novel character traits. This phylogenetic analysis not only establishes ancestral headgear morphology of Antilocapridae but allows inferences of major social structure changes. These results confirm previous works inferred through comparison with artiodactyl families that antilocaprids evolved from small-bodied monogamous pairs to large-bodied gregarious herds. Our findings show multiple originations of herding social behavior.
Open Access
A New Method of Genome-Scale Metabolic Model Validation for Biogeochemical Application
(University of Oregon, 2017-09-06) Shapiro, Benjamin; Jin, Qusheng
We propose a new method to integrate genome-scale metabolic models into biogeochemical reaction modeling. This method predicts rates of microbial metabolisms by combining flux balance analysis (FBA) with microbial rate laws. We applied this new hybrid method to methanogenesis by Methanosarcina barkeri. Our results show that the new method predicts well the progress of acetoclastic, methanol, and diauxic metabolism by M. barkeri. The hybrid method represents an improvement over dynamic FBA. We validated genome-scale metabolic models of Methanosarcina barkeri, Methanosarcina acetivorans, Geobacter metallireducens, Shewanella oneidensis, Shewanella putrefaciens and Shewanella sp. MR4 for application to biogeochemical modeling. FBA was used to predict the response of cell metabolism, and ATP and biomass yield. Our analysis provides improvements to these models for the purpose of applications to natural environments.
Open Access
After the Flow: Landscape Response to the Emplacement of Holocene Lava Flows, Central Oregon Cascades, USA
(University of Oregon, 2012) Deligne, Natalia; Deligne, Natalia; Cashman, Katharine
Effusive volcanic eruptions repave landscapes rapidly with lava flows, resetting the underlying landscape and ecosystem. The unique physical properties of lava pose interesting challenges for recovery, as lava flows can be highly permeable while lava itself is dense, sterile, and generally inhospitable towards life. This dissertation examines two aspects of landscape recovery following lava flow emplacement: (1) hydrologic adaptation of surface and groundwater to recent volcanism and (2) plant colonization of young lava flows. I examine two sites in the central Oregon Cascades: the c. 3 ka Sand Mountain volcanic field (SMVF), located in the headwaters of the McKenzie River, a critical water resource for the state of Oregon, and the c. 1.5 ka Collier Cone lava flow, originating on the north flanks of North Sister volcano. My investigation of the SMVF and upper McKenzie River watershed reveals a complex volcanic history with profound impacts on the configuration and short-term discharge of the McKenzie River: lava flows from the SMVF and other Holocene vents have buried, dammed, and altered the path of the McKenzie River. Moreover, given the large groundwater contribution from the SMVF to the McKenzie River, I estimate that SMVF activity caused McKenzie River discharge in present-day Eugene, Oregon to decrease by up to 20% for days to months at a time; future regional mafic volcanic activity could have a similar impact. The SMVF and the Collier Cone lava flow are notable for the juxtaposition of barren exposed lava and mature forests on the same or similarly aged lava flows. I use a combination of LiDAR analysis, field observations, and soil characterization to examine soil and vegetation at these two sites and find that the presence of an external soil source greatly facilitates plant establishment, growth, and survival. Here, external soil sources are syn- or post-eruptive tephra (SMVF) or flood-borne deposits (Collier Cone lava flow). External soil appears to provide a substrate for plants to grow in along with key nutrients and sufficient moisture; overall, external soil sources are key for the initial recovery following an effusive volcanic disturbance. This dissertation includes co-authored material submitted for publication.
Open Access
Analysis of an Exposed Portion of the Badwater Turtleback Shear-zone, Death Valley, California, USA
(University of Oregon, 2018-04-10) Jarrett, Corey; Miller, Marli
The exposed shear zone within the footwall of the Badwater turtleback presents an excellent opportunity to explore the brittle-ductile transition. Within this shear zone, a variety of lithologies preserve the last stages of crystal-plastic deformation concurrent with exhumation of the turtleback. The included field study captures a snapshot of each lithologic element during the last stages of ductile deformation. The exposed shear zone's journey through the brittle-ductile transition is analyzed using the deformation mechanisms of calcite and quartz. A history of strain partitioning is constructed through comparison of the strain and temperature environments needed to facilitate each mechanism of crystal-plastic deformation. As the shear zone cooled, strain was partitioned from quartz-rich mylonitic gneiss to the calcite-dominated marbles and mylonites. Correlation of deformation temperatures with previous studies further constrains the timing of the last stage of ductile deformation to between 13 and 6 Ma.
Open Access
Analysis of Off-axis, Low-velocity Zones on the Flanks of the Endeavour Segment of the Juan de Fuca Ridge
(University of Oregon, 2012) Wells, Anne; Wells, Anne; Hooft, Emilie
Seismic data from the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge reveal several crustal-level, low-velocity, high-attenuation regions on the eastern and western ridge flanks 7 to 16 km from the neovolcanic zone. I examine Pg amplitude anomalies for a wide variety of source-receiver azimuths in the Endeavour active source seismic tomography data. I use finite difference waveform forward modeling to estimate the dimensions, depth, and seismic properties of the best-observed inferred anomalous regions. The attenuating regions extend 10-15 km beneath axis-parallel bathymetric highs and from 2 to 4 km below the seafloor. The velocity reduction is small (~8%) and the attenuation large (QP ≈ 8-40) suggesting the presence of partial melt. I infer that melt focusing toward the neovolcanic zone is incomplete and that tectonic interactions with the Heckle seamount chain and/or the large segment-bounding overlapping spreading centers may promote off-axis melt delivery at the Endeavour segment.
Open Access
Ancient soils of Earth and Mars
(University of Oregon, 2023-03-24) Broz, Adrian; Roering, Josh
Three to four billion years ago the surface of Mars may have been habitable. Ancient martian rocks that were subject to aqueous alteration in near-surface environments may store a record of this habitable paleoclimate, and they may also be favorable environments for the preservation of biosignatures. Some of the oldest altered rocks on Mars appear to be similar in mineralogy and geochemistry to ancient, buried soils (paleosols) on Earth. By using terrestrial paleosols as an analog for Mars, this dissertation seeks to constrain the organic preservation potential of martian paleosols. This is a first step towards understanding if putative martian paleosols should be considered high priority targets for in-situ drilling campaigns and sample return to Earth.The objectives of this work were to a) identify the factors that have led to enhanced preservation of organic matter in terrestrial paleosols from throughout Earth’s 3.7 billion year old geological record; b) determine if the mineralogy and alteration history of Eocene (33 million-year-old) paleosols from eastern Oregon can be identified with Mars rover-like instruments; and c) determine if trace amounts of organic carbon in the Oregon paleosols can be detected with evolved gas analysis (EGA), a technique currently employed by the NASA Curiosity Mars Rover to search for past signs of life on Mars. A data compilation of previously published organic matter content of paleosols spanning ~3 billion years of Earth history showed that soil redox state before burial was a major factor that was associated with enhanced preservation of organic matter in paleosols. Chemically reduced paleosols were found to preserve organic carbon at abundances two to three orders of magnitude greater than oxidized paleosols. Next, evolved gas analysis, spectroscopy, and x-ray diffraction were determined to be suitable techniques for constraining the mineralogy and alteration history of 33-million-year-old paleosols from Oregon. Very low amounts of organic carbon (~0.01 wt. %) and fragments of organic molecules in oxidized paleosols were able to be observed with EGA, suggesting these techniques may be suitable for detecting low amounts of organic carbon in similar materials on Mars. This work indicates that putative paleosols / weathering profiles on Mars should be considered high priority targets for in-situ biosignature detection and eventual sample return to Earth.
Open Access
Anthropogenic and Non-Anthropogenic Contributions to End-Pleistocene Megafaunal Extinctions in the American West
(University of Oregon, 2019-09-18) Finkelman, Leonard; Davis, Edward
Widespread extinctions of mammalian megafauna at the end of the Pleistocene epoch remain insufficiently explained. In North America, approximately sixty megafaunal species disappeared in a window between 13 and 11 ka that is coincident both with large-scale climate changes and with human arrival on the continent. Analytical methods may distinguish these factors’ relative contributions to megafaunal extinctions. Here I give one such analysis for megafaunal taxa from the American west. I compiled a comprehensive chronology of fossil occurrences for eight taxa and used the Gaussian-resampled, inverse-weighted method to infer their likely true extinction dates; these inferences were then compared with human occupation, temperature, and palynological data from sites west of the North American continental divide. Results suggest that human activity, climate shifts, and vegetation change made distinct contributions to megafaunal extinctions. Ecological state shifts offer a unified account of the causal contributions of all three factors.
Open Access
Ash Sintering in the Presence of a CO2-H2O Vapor
(University of Oregon, 2018-09-06) Hoxsie, Erin; Reed, Mark
We carried out rhyolite ash sintering experiments in the presence of a mixed CO2-H2O vapor using both fine and coarse ash. Fine ash is barely sintered after 7 minutes and fully densified after about 30 minutes. Coarse ash is barely sintered after 45 minutes and fully densified after a few hours. Vesicle relaxation from initially angular shapes to spherical shapes takes longer than estimated from scaling relations. The experimental sintering and vesicle relaxation timescales substantiate the hypothesis that natural obsidian pyroclasts from Mono Craters, California (USA) form by ash sintering. Two observations are interpreted as the most direct evidence yet that CO2 flushing from a deeper magmatic was involved in the eruption: (1) the preservation of sharp-tipped vesicles in domains of clasts that have high dissolved CO2 concentrations, and (2) the anticorrelation between H2O and CO2 observed in multiple clasts. This thesis includes previously unpublished co-authored material.
Open Access
Assessment of Character Variation in the Crania and Teeth of Modern Artiodactyls for Better Species Diagnosis in the Fossil Record
(University of Oregon, 2016-11-21) Emery, Meaghan; Davis, Edward
Accurately distinguishing species in the fossil record is difficult when the extent of osteological variation in many modern animals is unknown. Research into intraspecific variation has been conducted in a number of groups, but has not been conducted for systematics use in most modern artiodactyls. In this dissertation I quantify intraspecific variation of teeth in 14 species of modern artiodactyl, then test how accurately cranial characters diagnose modern, sympatric species of duikers, and use this information to reassess the artiodactyl diversity of a fossil group: the superfamily Merycoidodontoidea in the John Day Fossil Beds. Ultimately, variation is not constant between orders or different size classes, is influenced by morphology, size, and dimorphism, and this variation should be incorporated into fossil diagnoses to avoid both overconfidence of diagnosis and under-recognition of possible intraspecific variation.
Open Access
Bed Force Distributions in Granular Flows
(University of Oregon, 2021-04-29) Winner, Amelia; Dufek, Josef
Granular flows are particle-laden gravity currents that are ubiquitous in nature in a variety of different geologic settings. Their high mobility and potential for harm to human populations and infrastructure motivate workers to better understand their dynamics in hopes of predicting their behavior and runout. Forecasting the movement of these hazardous flows, however, requires understanding the mass and momentum transfer between the flow and its substrate. In this dissertation, I analyze the normalized frequency-magnitude distribution of bed force excursions generated by idealized granular flows through a combination of laboratory experiments and discrete element simulations. I explore a wide range of flow behaviors by varying mean grain size, shear rate, and standard deviation of grain size. In the discrete element simulations, I also explore the role of interstitial fluids in determining the shape of the bed force distributions by varying fluid density and viscosity. The flows explored in this dissertation span three flow regimes, encapsulating elastic-quasi-static, elastic-inertial, and inertial-collisional behaviors. Resulting distributions show a dependence of the best-fit functional form on flow regime with diffuse boundaries between regimes. Bed force distributions are sensitive to changes in shear rate and the standard deviation of grain size, weakly sensitive to changes in fluid properties, and robust to changes in mean grain size. Distribution tails generally become more elongated with increasing values of inertial and Stokes numbers. The results of this work highlight the relative erosive potential for granular flows in different flow regimes, showing a higher erosive potential for flows exhibiting more inertial behaviors. In addition to my analysis of bed force distributions in granular flows, I explore the effects of sediment redistribution on sea level in the Bengal Basin and Ganges-Brahmaputra-Meghna river system which is responsible for transporting roughly 1 billion tons of sediment annually. Using a gravitationally self-consistent sea level model, I show that sediment redistribution in this region is likely responsible for ~ 30 m of sea-level change over the last glacial cycle, but the results of these simulations are sensitive to model input parameters such as the effective elastic lithospheric thickness and mantle viscosity profile.
Open Access
CALCULATION OF EMPIRICAL CORRELATION COEFFICIENTS IN MULTI-COMPONENT OXIDE SYSTEMS FOR THE REDUCTION OF ELECTRON MICROPROBE DATA
(University of Oregon, 1977-09) Dalheim, Peggy Ann
The purpose of this project was twofold - to synthesize several electron microprobe glass standards in the system: SiO2 - Al 2O 3 -- Cao -- MgO, and to utilize these standards in empirically calculating a set of binary correlation coefficients for use in the Bence-Albee data reduction method. Ten standards were prepared using the four end member oxides in coarse, crystalline form as starting materials (99.9+% purity). The careful synthesis and extensive analysis of the standards insured that they are homogeneous with compositions known to better than 5xl0- 4 oxide weight percent. The X-ray intensities measured for Si, Al, Ca and Mg in the standards and the oxides, plus the known compositions of the glasses provided the information necessary to empirically derive the set of binary correlation coefficients ("alpha factors") within the SiO2 - Al2O3 - CaO - MgO system.
Open Access
Carbon and Oxygen Isotope Fractionation in Laboratory-Precipitated, Inorganic Calcite
(University of Oregon, 2015-08-18) Baker, Evan; Watkins, James
Carbon and oxygen isotopes in calcite crystals provide a record of the environmental conditions under which the crystals formed. To investigate the influence of temperature, pH, and growth rate on isotope discrimination by calcite, we measured carbon and oxygen isotope fractionation through a series of calcite precipitation experiments at T = 25C and pH = 7.5 - 9.3. We observe that neither the carbon nor oxygen isotope compositions correspond to the theoretical equilibrium isotope fractionation between calcite and solution. We also demonstrate that the fractionation of oxygen isotopes between calcite and water decreases with increasing pH, consistent with available data from experiments in which the enzyme carbonic anhydrase was used. Finally, we compare the carbon and oxygen isotopes of our calcite crystals to those of biogenic carbonates. This thesis includes previously unpublished co-authored material.
Open Access
Characterization of Aftershock Sequences from Large Strike-Slip Earthquakes Along Geometrically Complex Faults
(University of Oregon, 2018-09-06) Sexton, Emily; Thomas, Amanda
Large earthquakes often exhibit complex slip distributions and occur along non-planar faults, resulting in variable stress changes throughout the fault region. To better discern the role of stress changes and fluid flow on aftershock sequences, we examine areas of enhanced and reduced mean stress along the structurally complex strike-slip faults that hosted the 1992 Landers, 2010 El-Mayor Cucapah, and 2016 Kumamoto earthquakes. We characterize the behavior of aftershock sequences with the Epidemic Type Aftershock-Sequence Model and use the Maximum Log Likelihood method to determine the optimal set of ETAS parameter values along each fault. This study indicates that extensional areas experience greater secondary aftershock triggering and a higher density of aftershocks directly following the mainshock, which could be attributed to fluid influx. However, our results also highlight some shortcomings of the ETAS model, including high parameter correlation, and influence of catalog size and magnitude cutoff on parameter estimations.
Open Access
Characterizing Ice-Magma Features in the Central Oregon Cascades
(University of Oregon, 2022-02-18) Colón Umpierre, Ana; Townsend, Meredith
Hogg Rock is a basaltic-andesite dome located in the Central Oregon Cascades. Its flat top, steep sides, and glacial striations and lakes have led to the interpretation that Hogg Rock was a dome that erupted subglacially. It is also highly fractured, a characteristic often found in ice-magma deposits. We mapped the fractures at Hogg Rock and found three different types of fractures: cube joints, plate joints (also known as entablature), and pseudo- columnar joints. We also mapped the orientations of the fractures where possible. We found that the fractures were mainly horizontal and radially oriented around the butte, suggesting that Hogg Rock cooled from the outside in, and further supporting the interpretation that Hogg Rock erupted subglacially. We also measured the fracture density of the joints, and found that the platey joints represented the finest scale of jointing.
Open Access
Characterizing Landslide Movement at the Boulder Creek Earthflow, Northern California, Using L-band InSAR
(University of Oregon, 2009-09) Stimely, Laura Lyn, 1982-
Spatial and temporal patterns of movement of the Boulder Creek earthflow were investigated using 26 interferograms derived from ALOS satellite radar images acquired between February 2007 and February 2008. Persistently unstable hillslopes in Northern California are ideally suited to the study of the dynamics and morphological signature of earthflows, as the deeply sheared melange lithology, high seasonal rainfall, and fast uplift rates promote widespread deep-seated landsliding. In addition to identifying multiple active landslides in the region, L-band InSAR reveals varying deformation rates in the accumulation, transport, and toe regions of the Boulder Creek earthflow. Downslope displacement rates up to 1.8 m/yr are observed on the earthflow over a I-year period. The pattern of deformation is similar to that observed from 1944-2006 inferred from aerial photography. Interferograms highlight spatially variable rates controlled by lithology and gullies, and movement correlates with seasonal rainfall with a phase lag of ~2 months.
Open Access
Characterizing the Solar Wind-Magnetosphere Viscous Interaction in the Outer Solar System: Analytical Assessment of the Probability of the Kelvin Helmholtz Instability Growth at Uranus and Neptune
(University of Oregon, 2022-02-18) Olsen, Angela; Paty, Carol
Uranus and Neptune have dynamic magnetopause interfaces to the solar wind due to the orientation of their rotation and magnetic axes. The magnetohydrodynamic plasma description suggests that solar wind conditions in the outer solar system encourage magnetosphere boundaries at Uranus and Neptune to be more Kelvin-Helmholtz (KH) unstable, but no quantitative assessment has been performed. This study employs an analytical model to test the condition for KH instability growth at the outermost planets in the solar system. The solar wind and tilted planetary magnetic field are separated by a surface representing the magnetopause. Values from each region are applied to the KH condition to evaluate if the instability is possible. The model is evaluated for both Uranus and Neptune at solstice and equinox geometries, under a variety of solar wind interplanetary magnetic fields, and over the course of its daily rotation.
Open Access
CHEMICAL CONTROLS ON THE BIOTIC AND ABIOTIC RELEASE OF CHROMIUM AND VANADIUM
(University of Oregon, 2024-03-25) Balogun, Fatai; Polizzotto, Matthew
Contamination of ground and well water by Cr and V from anthropogenic and geogenic sources has gained considerable attention over the last few decades due to environmental and public health concerns. The specific threat of Cr and V contamination is dictated by their redox speciation. In the natural environment, redox active phases such as ubiquitous Iron and manganese (oxyhydr)oxides are known to modulate mechanisms responsible for the mobility and bioavailability of Cr and V. Also, Cr and V availability is dependent on the reactivity of natural organic matter, which may serve as a major reductant of oxidized species, sorbent, and facilitator of mineral dissolution. Despite this knowledge, the specific constraints on the mechanisms of Cr and V oxidation, release, and retention by different organic carbon types, Fe and, Mn(oxyhydr)oxides in model and natural systems are not well understood. Accordingly, the objectives of this work were to (1) gain a more detailed mechanistic understanding of how organic carbon proxies and Mn-oxide influence Cr oxidation and release; (2) determine the host phases for Cr and V in aquifer materials and quantify their adsorption capacities; (3) determine the impact of organic matter and Mn-oxide proxies on the biotic and abiotic release of Cr and V in aquifer materials. Our experiments showed that aliphatic citric acid produced 8.5 times less Cr(VI) than aromatic gallic acid. In chemically variable saprolites, the affinity for V was 8 – 11 times greater than for Cr. Amorphous phases were inferred to be the major host phases for Cr and V. Lastly, organic carbon abiotically released Cr and V from solid host phases, while Mn-oxide influenced the release of Cr and V only in Redlair saprolite. This work underscores the need to integrate organic carbon types and mineralogical controls into predictive models for redox-sensitive metal dynamics and environmental availability. This dissertation includes previously published and unpublished coauthored material.
Open Access
Climate and Ecological Change in Oligo-Miocene Mammals
(University of Oregon, 2011-12) Orcutt, John D.
Whether or not a causal relationship exists between climate and mammal body size is one of the longest-standing and most intractable questions in ecology. The classic model of body size evolution (Bergmann's Rule) holds that body size is driven by temperature, but more recent hypotheses have suggested that other climatic variables or biotic interactions may play a more important role. The use of paleoecological data to address this question allows variables that are tightly correlated in modern ecosystems to be teased apart and allows body size patterns to be observed through time, adding an extra dimension to analyses. This dissertation details the findings of two paleoecological tests of Bergmann's Rule in the Oligo-Miocene (30-5 Ma), one tracking body size and climate through time in the northwestern United States and another tracking geographic body size trends through time along the west coast of North America. In both cases, body size was analyzed in three representative families of mammals: equids, canids, and sciurids. Such large-scale analyses are dependent on fossils that can be placed in a reliable taxonomic, geologic, and temporal context, and this dissertation also focuses on a reevaluation of the canid fauna of Oregon's Juntura Formation that places a critically important Late Miocene carnivore fauna in just such a context. Two genera of canids - Epicyon and Carpocyon - are described from the fauna for the first time, with important implications for regional biostratigraphy. The body size analyses show no consistent relationship between body size and any climatic variable. Further, body size patterns vary widely between taxa at several levels, suggesting that one universal driver of body size evolution does not exist. Not only is there no evidence for Bergmann's Rule in Oligo-Miocene mammals, but comparative analyses of geographic body size patterns in the modern genera Odocoileus, Canis, and Spermophilus fail to show the latitudinal gradients upon which Bergmann's Rule is predicated. The apparent existence of such trends in some taxa may be the result of anthropogenic extirpation at low latitudes, further underscoring the importance of including paleontological data when formulating models predicting the response of biotic variables to environmental change.
Embargo
Climate Regulates Stable Weathering Fluxes over Interglacial-Glacial Cycles
(University of Oregon, 2018-04-10) Schachtman, Nathan; Roering, Joshua
Feedbacks between climate, tectonics and erosion drive mineral dissolution in the subsurface and may provide strong controls on chemical weathering as a mechanism for modulating climate through CO2 drawdown. However, few quantitative evaluations of chemical weathering intensity or flux variations with time exist to support this hypothesized feedback. Trace element concentrations in colluvial sediment demonstrate that in unglaciated mid-latitude terrain, climate exerts a strong control on chemical weathering intensity and erosion over glacial-interglacial cycles by modulating the efficacy of abiotic and biotic processes. Weakly chemically altered sediment corresponds with high erosion rates during the Last Glacial interval (vice versa during the Holocene) such that we observe stable weathering rates despite variations in temperature and vegetation. Our results suggest that climate-weathering feedbacks in mid-latitude regions may be weaker than previously hypothesized and provide a new framework to explain stable solute fluxes over Milankovitch climate fluctuations.