Date of Award

2011

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Brenda L. Hall

Second Committee Member

Michael R. Kaplan

Third Committee Member

Jorge Strelin

Abstract

Variations in Earth‘s orbital parameters affect insolation and are thought to drive ice-age cycles (Milankovitch Theory). Northern and southern mid-latitudes show opposing insolation signals, because of the effect of precession. Despite this difference, paleoclimate records from both hemispheres display broadly synchronous glacialinterglacial climate changes tied to northern hemisphere insolation. This would imply that southern hemisphere glaciers advanced in the face of increasing local summer insolation during the last glacial maximum and thus raises questions about the orbital theory of ice ages. Well-dated paleoclimate records are important for testing hypotheses concerning the origin of ice ages, particularly in the southern hemisphere. Glaciers are sensitive recorders of past climate. In this thesis, I used precise mapping of moraines deposited by outlet glaciers, together with 10Be exposure and radiocarbon ages, to establish the timing of ice fluctuations throughout the last glacial period in Torres del Paine, Patagonia (51°S). I also determined the relationship of ice fluctuations to potential forcing factors, such as insolation and CO2. My data show that the Patagonian ice sheet deposited seven moraine belts in the Torres del Paine region during the last ice age, with advances to the outer moraines at ~49,000, 41,000, ~16,500 and 14,200 years ago. Glacial fluctuations were accompanied by the formation of paleolake Tehuelche. Maximum ice extent occurred during MIS 3, a finding that has been documented so far only rarely in South America. The chronology also shows that the Patagonian ice sheet expanded between 14,200 and 12,600 ka, providing conclusive evidence for the full duration of the Antarctic Cold Reversal in the southern mid-latitudes, as recorded by glaciers. I conclude that southern mid-latitude glacier expansions occurred irrespective of the insolation phase and seem to have coincided with stadials in Antarctica and northern shifts of the southern westerly wind belt, which likely played a key role driving near simultaneous changes throughout the southern hemisphere.

Download

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Included in

Glaciology Commons

Share