Multiple glacial maxima of similar extent at ∼20-45 ka on Mt. Usborne, East Falkland, South Atlantic region

The pattern, timing, and origin of Southern Hemisphere climate change during the last glaciation remains a pressing problem, with implications for the role of orbital forcing in ice-age cycles. Here, we present geomorphological and cosmogenic exposure age data from East Falkland in the South Atlantic region that show onset of glacial conditions by marine isotope stage 4 (similar to 60-70 ka), with expansion of ice to its maximum extent of the last glaciation. At least seven geomorphological units marked by multiple crests on composite moraines indicate glacier expansion on Mt. Usborne, the highest peak of East Falkland. From similar to 20 to 45 ka, glaciers fluctuated on a millennial timescale with near-maximum conditions being reached repeatedly. Overall ice extent appears to have shrunk slightly through time, with evidence of glaciation at similar to 20 ka preserved only in the highest-elevation cirques. This long glacial maximum is inconsistent both with local orbital control and orbital forcing as expressed in the traditional Milankovitch hypothesis. The timing of millennial glacier expansions occurred between Northern Hemisphere Heinrich Stadials and resembles that documented for New Zealand glaciers, suggesting at least a trans-Pacific expression. We postulate that periodic recessions corresponded with southward expansion of the southern westerlies during Heinrich Stadials and warming air and ocean temperatures over the South Atlantic region. (C) 2020 Elsevier Ltd. All rights reserved.