Theses Defenses

Bradley Keith B.S.

M.S. candidate
Advisor: Dr. Samantha Bova

Half-Precession Pacing of the Southern Westerly Winds and the Patagonia Ice Sheet over the Last 900,000 Years

Friday, April 26, 2024 at 9:45 am
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Abstract
Reconstructions of the Patagonian Ice Sheet (PIS) indicate a high sensitivity of the ice mass to changes in Southern Hemisphere climate. The longest of these records, however, is constrained to the last glacial-interglacial cycle which limits our understanding of ice-ocean-atmosphere linkages on orbital timescales. Here, we present a 900 ky record of bulk sediment geochemistry at Site J1001 located ~120 km offshore of Patagonia. We find that variations in the terrigenous sediment geochemistry at site J1001 are dominantly controlled by provenance changes, which are linked to variations in the extent of the PIS. We find two primary sediment endmembers through a factor analysis consistent with previous studies: one sourced primarily from the Andes Mountain range, enriched in Fe and Ti, and one from coastal source rocks, enriched in Rb. The relative abundance of these sediment endmembers varies at glacial-interglacial, obliquity, and unexpectedly, half-precession timescales. We link variability in these endmembers to changes in the extent of PIS, with more Rb-rich coastal sourced sediment being deposited at J1001 during glacial periods when the ice sheet extends towards the coast. We further suggest that the half-precession signal arises due to the location of J1001 near the midpoint of the SWWs latitudinal range, which results in the mean position of the winds, and thus maximum precipitation, passing overhead twice a precession cycle, bringing increased precipitation and fueling advances in the central PIS edge during glacial intervals. These results suggest that advance and retreat cycles of the PIS are highly sensitive to variations in the position of the SWWs via their influence on regional precipitation balance. 

Gabriella Mann

B.S. candidate
Advisor: Dr. Samantha Bova

CO₂ drives sea surface temperatures in the Eastern Equatorial Pacific during Marine Isotope Stage 9

Friday, April 26, 2024 at 10:30 am
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Abstract
There is limited research on the mechanisms that drive sea surface temperatures (SSTs) in the Eastern Equatorial Pacific (EEP). The Pacific is the largest ocean basin and contributes proportionally to heat transport across the globe, making it an important area for understanding global SSTs. The purpose of this study is to investigate the SSTs during Marine Isotope Stage 9 (MIS 9), an interglacial period dated from 337,000 to 300,000 years ago, to better understand the climatic patterns of this period. This research investigates the transition from interglacial to glacial conditions during the late stages of MIS 9, focusing on variations in SSTs and their potential drivers. Alkenone paleothermometry methods were applied to samples from Ocean Drilling Program (ODP) Site 1240 in the EEP to reconstruct past SSTs. These methods indicate that atmospheric CO2 levels are a primary driver of tropical SSTs, even in regions characterized by strong upwelling. Findings show a temporal SST range from 22.79°C to 26.02°C that indicates a correlation between increased atmospheric CO2 levels and higher SSTs. Contrasting with previous studies that highlighted oceanic processes like upwelling, this research highlights CO2 as a dominant mechanism driving SSTs during MIS 9. These results suggest the necessity for further research into the role of CO2 in SST regulation and its implications for future climate models.

Jennasea Fisher

B.S. candidate
Advisor: Dr. Matthew Weingarten

Evidence for Active Faults as Hydraulic Barriers to Groundwater Flow in Warner Springs Basin

Friday, April 26, 2024 at 11 am
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Abstract
Fluid flow along active faults can play a crucial role in the long-term fault behavior as fault permeability exhibits a strong control on stress accommodation at depth (Hill et al., 2023). Broadly speaking, the spatial distribution of fault hydraulic properties within the southern San Andreas Fault system, encompassing the San Andreas Fault (SAF), the San Jacinto Fault (SJF) and Elsinore Fault (EF), are constrained poorly. Here, we aim to investigate the hydrogeologic properties of the fault strands along the Julian section of the Elsinore Fault within Warner Springs Basin. We focus our study on discerning whether the mapped faults serve as groundwater flow conduits, barriers or conduit-barrier systems. Within our study area, the Agua Tibia South and Agua Tibia North faults are both NW-SE trending, subvertical, right-lateral strike slip faults, which are constrained from well logs and prior surficial geologic investigations. The coexistence of active, well-constrained fault geometries, as well as long-term pumping and monitoring well data within the basin made Warner Springs a prime candidate to investigate fault hydrogeologic properties. We hypothesize the active faults in Warner Springs subbasin act as barriers to flow, resulting in observable differences in groundwater response to pumping from one fault compartment to another. The methods used in this analysis include kriging techniques in ArcGIS Pro for spatial interpolation, time series analysis to compare pumping and monitoring well data, and the Cooper-Jacob Method to estimate hydraulic conductivity of pumping-monitoring well pairs. Preliminary results reveal a complex hydrogeological landscape, suggesting a combination of groundwater flow barrier and conduit-like behavior across the basin’s faults. Time-series analysis of pumping and monitoring well data show the Agua Tibia South Fault predominantly exhibits barrier-like behavior, compartmentalizing the upstream and downstream portions of the watershed. Spatial interpolation of monitoring well data shows additional evidence for barrier-like behavior as mapped water levels are elongated along-strike of some of the mapped faults within the subbasin. Hydraulic conductivity estimates range over two orders of magnitude with lower conductivity values estimated north of the Agua Tibia South Fault and higher values estimated south of the fault. These findings just scrape the surface of the complex interplay between fault structures and groundwater flow in the basin, but show promise for better understanding the hydraulic behavior of faults within the subbasin.

Caitlin O’Keefe

B.S. candidate
Advisor: Dr. Rafael Almeida

Defining the Main Martir Thrust in Bahia De Los Angeles, Baja California, Mexico

Friday, April 26, 2024 at 11:30 am
watch Caitlin’s talk

Abstract
This research endeavor aims to locate the Main Martir thrust outside Bahia de Los Angeles, through comprehensive field mapping techniques, age dating methodologies, examination of thin sections, and data analysis. The ductile thrust marks a significant boundary, presumed to be a suture, marking the collision between continental basement with an oceanic basin and island arc. The study aims to furnish a more detailed understanding of the Main Martir Fault and provide a comprehensive structural analysis of the field area.

Casey Schroeder

B.S. candidate
Advisor: Dr. Anna Foster

Using InSAR to determine surface deformation along Northern Ecuador’s active fault system

Friday, April 26, 2024 at 12 pm