Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Aaron E. Putnam

Second Committee Member

George H. Denton

Third Committee Member

Joerg M. Schaefer

Additional Committee Members

Brenda L. Hall

Gordon R.M. Bromley

Peter O. Koons

Kirk A. Maasch

Abstract

Late-Pleistocene glacial cycles represent the largest natural changes to Earth’s climate over the past one million years, and yet determining the underlying drivers remains a major mystery in paleoclimate. The observation of generally synchronous glaciation and deglaciation between the polar hemispheres (Mercer, 1984) runs contrary to long-standing ice age theory (e.g. Milankovitch, 1941), and was recently dubbed ‘Mercer’s Paradox’ (Denton et al., 2021). In this thesis I derive regional climate records from mountain glaciers along an interhemispheric Australasian transect, extending from the Mongolian Altai to the Southern Alps of New Zealand, to test the existence of Mercer’s Paradox in the Asia-Zealandia sector of the planet, just as Mercer (1984) had observed for North and South America. My approach involved developing high-resolution geomorphologic maps, 10Be surface-exposure chronologies, and snowline reconstructions from glacial landforms in the Altai Mountains of Western Mongolia (49°N), the Southern Alps of New Zealand (44°S), and the Shaluli Shan of the southeastern Tibetan Plateau (30°N) in order to document regional climate changes marking the most recent ice age (i.e. the Last Glaciation; ~70 – 18 ka; Denton et al., 2021) and subsequent warming (i.e. the last glacial termination; ~18 – 11 ka; Denton et al., 2021). My results show that mountain glaciers in the Mongolian Altai (49°N) achieved maximal extents at the same time as mountain glaciers in New Zealand (44°S), despite being located in opposing polar hemispheres and in different climate regimes (continental vs. oceanic). In addition, mountain glaciers in the monsoonal high-elevation Tibetan Plateau (30°N) also fluctuated in concert with mid-latitude glacier systems during the Last Glaciation and last glacial termination. These mountain glacier records reveal the existence of Mercer’s Paradox in the Asian/Australasian sector of the planet and indicate that any solution to the problem of Late-Pleistocene glacial cycles must account for synchronous behavior of mountain glaciers in both hemispheres during the last glacial cycle, likely driven by rapid changes in the radiation budget of the planet. I suggest that heat export from the Indo-Pacific Warm Pool may be an important driver responsible for unifying millennial-scale glacier records from around the globe during the late Pleistocene, as well as driving mountain glacier ice loss during the last glacial termination that was sufficiently rapid to outpace other proposed radiative forcing agents.

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