GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION DISTINGUISHED CAREER AWARD: A REMARKABLE CLIMATE CHANGE IN THE SOUTHERN HEMISPHERE

How the planet emerged from the depths of the last ice age remains an unresolved problem of paleoclimatology. Here I illustrate that in the Southern Hemisphere this transformation featured a remarkable climate change in which 75% of the glacial-interglacial warming occurred in the interval between 17,800 and 16,500 yrs ago. The data for this conclusion come from glacier-inferred temperature reconstructions in the Andes and the Southern Alps, from tree-line rise in the Chilean Lake District, and from a temperature reconstruction from the new WAIS-Divide Antarctic ice core. These records all reflect sharp and immediate responses to temperature changes in the atmosphere. Together, they indicate a synchronous, rapid, and sustained warming that began 17,800 yrs ago and spanned at least 110⁰ of longitude and at least 40⁰ of latitude. Comparison of these records shows that the amplitude of the glacial-interglacial temperature change for Antarctica (~12⁰C) was about twice that for middle southern latitudes (~6⁰C), presumably because of the amplifying effect of Antarctica’s sea-ice apron.

This decisive warming that ended the last glaciation in southern latitudes may have resulted solely from the far-field effects, through the bipolar seesaw, of the Northern Hemisphere Heinrich stadial 1. However, the warming had a rapidity, extent, and magnitude suggestive of a switch between stable modes of operation of a climate system that is linked together in a nonlinear fashion and thus is susceptible to rapid reorganizations. In such a case, Heinrich stadial 1 may have served simply as the trigger for such a reorganization.