Multiple glacial maxima of similar extent at ~20e45 ka on Mt. Usborne, East Falkland, South Atlantic region – Quaternary Science Reviews – B.L. Hall, T.V. Lowell, P. Brickle

ELSEVIER – Quaternary Science Reviews 250 (2020) 106677


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 (~60e70 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 ~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 ~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.