Date of Award

Spring 5-2018

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Quaternary and Climate Studies

Advisor

Aaron Putnam

Second Committee Member

George Denton

Third Committee Member

Brenda Hall

Additional Committee Members

Karl Kreutz

Alice Doughty

Abstract

The last glacial termination (~19-11 ka) marks the end of the last ice age and the transition to modern interglacial conditions. The mechanisms that triggered deglaciation are unresolved. Various hypotheses for deglacial warming involve changes in Earth’s orbit, an 80-ppm increase in atmospheric CO­2, a ‘bipolar seesaw’ in oceanic-heat redistribution, and shifting wind belts. Here, I present a 10Be surface-exposure chronology for a system of glacial landforms in the Tsagaan Gol-Potanin Glacier valley in the Mongolian Altai (49°N, 88°E) to determine the nature of the termination in interior Asia. Located near the center of Earth’s largest continent, the glaciers in the Mongolian Altai are well situated to test the roles of various climate mechanisms in driving the last glacial termination. My chronology is underpinned by detailed glacial-geomorphic maps made using satellite and drone imagery. The surface-exposure chronology reveals that moraine formation occurred at 23.24 ± 0.50 ka and 28.08 ± 0.58 ka during the local Last Glacial Maximum (LLGM). Glacial erratics bracketing small, discontinuous moraines are the youngest samples from the LLGM, ranging from 19.54 ± 0.36 ka to 22.11 ± 0.41 ka. The termination is documented by glacial erratics on a mid-valley bedrock mountain, Holy Mountain, and erratics next to the modern Potanin Glacier. The Holy Mountain samples record 253 m of ice-surface lowering between 18.23 ± 0.34 ka and 15.69 ± 0.34 ka. Glacial erratics outboard of the Potanin Glacier form two populations, at 16.20 ± 0.09 ka and 17.71 ± 0.19 ka, indicating that the termination was underway by 17.71 ± 0.19 ka. I reconstructed paleo-snowlines using the accumulation-area ratio (AAR) method to translate the glacial record into a climate signal. From the LLGM to modern, snowline rose 1100 ± 90 m, equating to a temperature increase of 6.0 ± 0.5°C using a lapse rate of 0.0055°C/m. At least 640 ± 90 m of snowline rise, or 3.5 ± 0.5°C of warming, occurred by 17.71 ± 0.19 ka. Rising atmospheric CO2 and reorganization of North Atlantic oceanic circulation lag the warming documented in this study. Possible mechanisms for deglaciation in the Mongolian Altai include rising local summer insolation, poleward heat export from the tropics, or a poleward shift of the westerly wind belts.

Comments

As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.

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