THE LAST TWO GLACIAL MAXIMA RECORDED IN MIDDLE LATITUDE ARGENTINA

Understanding to what extent, and why, the Northern Hemisphere may have influenced global climate during the glacial period requires adequate spatial coverage of well-dated geologic records to ascertain differences and similarities between regions. Mapping and ¹⁰Be and ²⁶Al cosmogenic dating are used to estimate the timing of the last and penultimate glacial periods, between ca. 25,000 and 15,000, and ca. 175,000 and 125,000 years ago, respectively, in middle latitude Argentina, 46.5° S. Following a major advance during marine isotope stage 6, the next time glaciers reached a maximum extent was between ca. 25,000-20,000 years ago. During marine isotope stage 2 at least six glacial events occurred in less than ca. 10,000 years on the eastern side of the Andes, reflecting millennial scale climate change in Patagonia during this time. If a marine isotope stage 4 event occurred in Patagonia, it was the same extent or smaller than the last glacial maximum. In middle latitude Argentina, the timing of the last glaciation and deglaciation was broadly in phase with that in the Northern Hemisphere. Our findings are consistent with other glacial geologic (and ice core and pollen studies), which, collectively, suggest that glacial advances occurred throughout most of South America on millennial time scales during marine isotope stage 2. This major glaciation occurred despite a high in local insolation at ca. 20,000 years ago; exceptions, where ice did not advance, must reflect a local mechanism such as a severe lack of precipitation for glacial growth.