The Last Glacial Maximum
We used 5704 14C, 10Be, and 3
He ages that span the interval from 10,000 to 50,000 years ago
(10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global
ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions
occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern
summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all
ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in
these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an
increase in northern summer insolation, providing the source for an abrupt rise in sea level. The
onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent
with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.
Publication Date: 2009
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