Contributor

Maria Beatrice Magnani

Subject Area

Earth, Atmospheric and Marine Sciences

Abstract

Over the past few decades, the notion of exogenic processes (e.g. weathering, erosion) contributing to mountain building rather than destruction has become increasingly supported through both direct observations and modeling. As a result, the details of the link between erosion, and therefore climate, and the tectonic evolution of mountain ranges, have progressively become established. One of the key observations emerging from the climate-tectonic debate has been the role of glaciers as powerful landscape sculptors, sensitive to climate signals. The reconstruction of glacial environments evolution and the recovery of patterns of glacial erosion over time have proven key to understanding feedbacks between climate and tectonic processes. Particularly glacial erosion rates show a marked increase toward the present, attributed to an increased variability of the climate in the last few million years. Whether this increase represents a genuine signal or is the result of a time averaging bias is still debated. To date, rates of glacial erosion and glacial erosion controls remain poorly understood, due to our lack of direct observation, particularly over different time scales, and due to poor preservation of glacial landforms in subaerial conditions. The sedimentary record preserved subaqueously in proglacial environments has the potential to offer observational constraints for understanding the relationship between climate, erosion, and tectonics. This dissertation addresses glacial erosion rates by providing first-order constraints on 1) the evolution of glacier grounding line positions through time as expressed in proglacial subaqueous settings, 2) the variations in sediment yields and erosion rates associated with glacial retreats and re-advances, and 3) the variables controlling erosion rates of lake-terminating glaciers. In this dissertation, I focus on the Southern Patagonia Icefield, where I reconstruct the subaqueous evolution and calculate new glacial erosion rates estimated from sediment accumulations in Lago Argentino, a proglacial basin with a nearly complete preserved sedimentary record. I use high-resolution seismic reflection data to examine the stratigraphic record in Lago Argentino and to constrain the timing of deposition in the context of the existing glacial chronology of the area. I identify subaqueously-preserved evidence of glacier readvances during the Last Glacial Termination, a record that has been missing from the terrestrial glacial landforms in the area, and that supports a broad synchronous response of Southern Patagonian glaciers to deglacial climate forcing. I use the interpreted seismic units and their corresponding timing to calculate erosion rates through the past ∼20,000 yrs, averaged over time intervals ranging from sub-decadal to millennial. I explore erosion rates variability through time and with changes in temperature, precipitation, retreat rates, and ice velocity. The data show that erosion rates have varied substantially, from 0.4±0.1 to 82.4±17.6 mm/yr, with no systematic increase (or decrease) through time. Rather, erosion occurs during discrete, intense events separated by times of quiescence. In addition, I find that glacial erosion rates have comparable magnitudes when averaged over similar time intervals. The data show a power-law increase in glacial erosion rates with decreasing averaging time interval, consistent with other observations globally. Given the observed intermittent character of glacial erosion, I attribute this increase to a time averaging bias, rather than to an escalation in magnitude of erosional pulses toward the present. I also find that glacial erosion rates for one of the fastest retreating glaciers in the Southern Patagonia Icefield, the Upsala Glacier, exhibit a strong positive correlation with retreat rates and ice velocities, facilitated by the temperate climate of Patagonia and modulated by the overdeepened lake bathymetry and distribution of subaqueous moraines.

Degree Date

12-2024

Document Type

Dissertation

Degree Name

Ph.D.

Department

Roy M. Huffington Department of Earth Sciences

Advisor

Maria Beatrice Magnani

Second Advisor

Matthew Hornbach

Third Advisor

Brian Stump

Fourth Advisor

Crayton Yapp

Fifth Advisor

Emi Ito

Number of Pages

119

Format

.pdf

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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