Date of Award

Spring 5-9-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

First Committee Advisor

Brenda Hall

Second Committee Member

Aaron Putnam

Third Committee Member

George Denton

Additional Committee Members

Jacquelyn Gill

Aaron Diefendorf

Thomas Lowell

Joellen Russell

Abstract

The mid-latitude westerly wind belts have been linked to abrupt climate change on regional and global scales. In particular, migration of the Southern Hemisphere westerlies (SHW) has been proposed to have had a role in the termination of the last ice age and possibly in shorter-term abrupt changes. My dissertation focuses on two sites to reconstruct the movement of the westerly wind belts and to explore the link between mean-annual wind position and climate change. Using a novel plant wax isotope record from lake sediments on Mt. Usborne (52 °S, 59 °W), East Falkland, in the South Atlantic, I constructed a multiproxy climate record from a sediment core spanning the last 23 ka (thousands of years before the present day) that documents poleward movement of the SHW during Termination 1, possibly linked to increasing winter duration. I also explored the effect that the changes to the position of the SHW at Mt. Usborne had on local plant communities during the Holocene, with relevance for future ecology. Pollen records document a highly resilient plant community, which shows only minor changes in response to shifts in moisture availability brought about by variations in SHW influence. Finally, at Baboon Lakes (37 °N, 119 °W) in central Sierra Nevada, California, I reconstructed not only changes in the mean annual position of the Northern Hemisphere westerlies (NHW), but also an independent record of fire history and water availability. With this multiproxy data set, I assess the linkage between the location of the wind belt and droughts in the American West. The data show changes in the position of the winds over the last 12 ka, with a particularly prominent poleward shift at ~8.3 ka. This movement was accompanied by decreased moisture availability and a sudden rise in forest fires as the influence of the NHW decreased. This shift to a poleward shifted NHW and the onset of the mid-Holocene warm, dry period of the American West does not seem to be driven solely by ice sheet dynamics, insolation, or North Atlantic teleconnection. More records across the region are needed to resolve the driver(s) at play.

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