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Figure 10.5. Extent of Northern Hemisphere glacial ice during the Last Glacial Maximum
(from Denton and Hughes (eds.), 1981 , by permission of John Wiley and Sons).
δ 18 O in ice cores means colder conditions over Greenland. A higher percentage
of left-coiling N. Pachyderma (a cold water planktonic foram) is interpreted as
lower sea surface temperatures. The scale for the percentage of N. Pachyderma
is reversed, providing easier comparison with the ice core record. Changes often
began and ended rapidly - much faster than indicated in this low-resolution figure.
We will return to this issue shortly.
The LGM occurred anywhere from 18-25 ka, depending on the region and inter-
pretation. In Figure 10.2 , we see a minimum in δ 18 O (i.e., coldest conditions) at
stage 2.2, around 18 ka. Figure 10.5 summarizes the approximate extent of Northern
Hemisphere ice sheets during the LGM. Although some aspects of this figure are
controversial and some have been revised (see later discussion), it makes the funda-
mental point that glaciation was widespread. The Laurentide Ice Sheet was the larg-
est after that of Antarctica. It covered most of Canada, merging in the west with the
Cordilleran Ice Sheet and the Innuitian ice sheet over the Canadian Arctic islands,
and reaching into the northern United States. Moraine features such as Cape Cod
and Long Island are geomorphological relics of the Laurentide Ice Sheet. In Europe,
the Fennoscandian (or Scandinavian) Ice Sheet covered Scandinavia and part of
western Russia. Glacial ice covered parts of the ocean shelf areas off northwest
Russia but most of Siberia was ice free. During the LGM, sea level was 120-135 m
lower than today. The Bering land bridge, connecting eastern Siberia with western
Alaska, last emerged at about 70 ka. The land bridge is of great anthropological
importance in that it allowed the migration of humans into North America.
Deglaciation - the transition from the LGM to the Holocene, was not a period
of uniform warming, but was interrupted by cold events. The most notable was the
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