Date of Award

Fall 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

First Committee Advisor

Brenda Hall

Second Committee Member

Tom Lowell

Third Committee Member

Aaron Putnam

Additional Committee Members

George Denton

Abstract

An Abstract of the Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science (in Earth and Climate Sciences)

May 2025

What causes ice-age terminations? The longstanding view is that glacial cycles are controlled by the intensity of summertime insolation in the high-latitude northern hemisphere that are somehow propagated globally. However, alternate hypotheses have emerged that cast doubt on this traditional view. As a first step toward testing different hypotheses, my goal is to reconstruct summer temperature change in the southern mid-latitudes to examine whether the last ice-age termination (17.8 - 11.7 ka) was synchronous or asynchronous across the globe. I focus in particular on the timing of the Antarctic Cold Reversal (ACR, 14.7-12.9 ka). Here, I present the first glacial geochronologic record of ice extent at Bahía Penhoat (55°S, 69°W) near the southernmost tip of South America. There are few highly resolved glacial records south of 50°S that span the ACR, making this new record important in tracking past climate changes at hemispheric and global scales.

To carry out this work, I use UAV-derived geomorphological mapping, along with 10Be surface exposure dating techniques. I then compare this record from Bahía Penhoat with previously collected data across southern South America and New Zealand, as well as in Scotland and Norway. My record suggests that the ACR culminated at 13.3±0.6 ka at Bahía Penhoat. The timing of this climate reversal is coeval with moraine construction farther north in

Argentina, across the Pacific Ocean in New Zealand, and in the northern hemisphere in both Norway and Scotland. This evidence suggests that climate conditions during this portion of the termination are globally synchronous, and thus proposed mechanisms that result in asynchronous climate behavior (e.g., the bipolar seesaw) are inconsistent with my analysis. Instead, a mechanism that can account for a globally synchronous signal, such as the Zealandia Switch, which invokes shifting of the southern hemisphere westerly winds, is necessary.

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