Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Aaron E. Putnam

Second Committee Member

George H. Denton

Third Committee Member

Brenda Hall

Additional Committee Members

Katherine A. Allen

Alice Doughty

Abstract

Here I use geomorphic mapping and 10Be surface-exposure dating to address the paradox that lies within the general understanding of the mechanisms driving ice-age climate and glacial cycles. The long-standing and widely accepted Murphy-Milankovitch hypothesis suggests glacial cycles are controlled by the local intensity of summer-time insolation. By this hypothesis, glacier maxima should be achieved at times of low insolation intensity and asynchronously between the polar hemispheres, a pattern which is inconsistent with the glacial geomorphic record. The 10Be chronology I have constructed of moraines at Soda Lake, Wind River Range, Wyoming, U.S.A. shows nine glacial advances to near maximal conditions 144.8 ± 4.0 kya, 44.6 ± 1.6 kya, 32.5 ± 1.0 kya, 30.1 ± 0.9 kya, 27.5 ± 0.8 kya, 23.2 ± 0.6 kya, 21.9 ± 0.6 kya, 20.7 ± 0.6 kya, and 19.6 ± 0.6 kya. Glacial maxima occurred at Soda Lake during times of various local summer insolation intensities, indicating that the Murphy-Milankovitch hypothesis is not a sufficient mechanism for explaining ice-age climate dynamics. Not only does the Soda Lake chronology show glacial maxima occurring through an entire insolation cycle, but it also provides evidence for synchronous glaciation between the polar hemispheres when compared to chronologies from the Southern Alps, New Zealand; Chilean Andes, South America; and Falkland Islands, Southern Atlantic Ocean. Records from these austral locations also indicate that glacier extent is not controlled by local summer insolation. Any proposed driver of ice-age climate must account for the bi-hemispheric synchrony of glaciation shown here along with the paucity of control that local summer insolation intensity has over glacier extent.

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