Date of Award

Summer 8-20-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Aaron Putnam

Second Committee Member

Joellen Russell

Third Committee Member

George Denton

Additional Committee Members

Kirk Maasch

Sean Birkel

Abstract

Deciphering causes of glaciations and their abrupt terminations over the last >700,000 yrs remains an important problem for understanding the behavior of the climate system and how it might change in the future. In particular, the role of the Southern Hemisphere (SH) Westerlies in global change has arisen as an important research direction. Glaciers are highly sensitive to climate change. Examination of mid-latitude glaciers under the influence of westerly wind systems in both hemispheres can help provide insight into the role of the Westerlies in climate change. In this thesis, I present a twofold strategy to refine knowledge of the links between behavior of the Westerly wind systems and glaciation: 1) I present an analysis of modern glacier snowline datasets together with results from a state-of-the-art climate reanalysis to evaluate modern controls glacier behavior. 2) I provide a paleoclimate perspective on the role of the SH Westerlies in glacial climate by presenting and interpreting a 10Be chronology of terminal moraines constructed by the former ice-age Pukaki glacier, Southern Alps, New Zealand. First, I compared climate reanalysis data products and glacier snowline elevations from the antipodal Southern Alps of New Zealand and the European Alps to evaluate how broadly these glacier systems monitor atmospheric circulation. I derived empirical orthogonal function principle components of the snowline datasets and then determined correlations with climate data using the Pearson’s correlation method. The robustness of the results were evaluated using a student’s t-test, a detrending sensitivity test, and a Monte-Carlo analysis. Our results show strong regional (European Alps) and pan-hemispheric (Southern Alps) correlations between glacier snowlines and summer temperature at all levels of the troposphere. Snowlines also exhibit strong positive correlations with the latitude of the westerly jets in respective hemispheres. Our results indicate that (1) these glacier systems monitor atmospheric temperature on wide spatial scales, and (2) the westerly winds exert a first-order control on modulating the proportion of cold vs. warm air masses passing over these glacier systems. Second, I examined the paleo-glacier record of the Southern Alps of New Zealand to evaluate the role of the Westerlies in SH ice-age climate. In particular, I examine an important problem known as ‘Mercer’s Paradox’, which is based on the observation that glacier systems in both hemispheres achieved ice-age maxima contemporaneously, despite opposing solar intensity signals. To address this problem, I present a 10Be chronology of terminal moraines constructed by the Pukaki glacier during the peak of the last ice age in the Southern Alps. My results indicate that the Pukaki glacier terminus achieved its greatest extent of the past ~65-kyrs at 20 kyrs ago, in concert with the maximal extents of Northern Hemisphere ice-sheet volume and mountain glacier maxima. These results further reinforce Mercer’s Paradox. They are also consistent with the behavior of the SH Westerlies. I suggest that the influence of equatorward-shifted austral Westerlies on Southern Alps glaciers during the last glacial maximum (LGM), and on the climate system as a whole, may provide a solution to Mercer’s Paradox. Taken together, the results from these two chapters of this thesis highlight the utility of glacial measurements as metrics for atmospheric temperatures and wind belt positions in the past, present, and future. As the planet responds to the increasing atmospheric CO2 burden, the combined impacts of global tropospheric warming and poleward-shifting westerlies will likely drive accelerated snowline rise and enhanced melt of mid-latitude glaciers in both hemispheres, much like what happened during the warming that terminated the last ice age.

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