Life and climate in an ice age - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 2

that the world was a stormy place with high winds that whipped up dust from
land and salt from oceans. The dustiness would suggest that many areas of the
Earth were arid. And indeed, the prevailing view seems to be that the Earth was
predominantly arid during ice ages, although some areas, particularly the
Southwestern U. S., were extremely wet. Yet, there had to be winds that carried
moisture to northern climes in order to drop some 10 12 m 3 of ice per year on the
growing ice sheets. Since the temperature drop during ice ages at high latitudes
was far greater than the temperature drop in the tropics, the temperature differen-
tial between the tropics and polar areas was greater during ice ages, creating a
greater driving force for flow of atmosphere toward polar areas.
A comparison of the distribution of vegetation for all the continents of the
world at the height of the last ice age with the distribution today was provided by
Adams and Faure (1997). Their comparison for North and Central America is
provided here in Figures 1.1 and 1.2 . According to this model, the distribution of
flora (and presumably fauna as well) migrated toward the equator during ice ages,
and areas adjacent to the ice sheets were converted to tundra and semi-desert.
Burroughs (2005) provides a similar flora map of Europe.
Barton et al. (2002) provide a window into life, flora, and fauna in North
America as the last ice age began to wane:
''Flying over the ice fields of Canada it is easy to imagine being back in the
last Ice Age. There is ice as far as the eye can see. Glaciers roll down the valleys,
towering ice sculptures rise out of the mountainsides, and exquisite turquoise
pools glisten in the fissures below.''
Figure 1.3 shows the Wrangell-Saint Elias ice field on the Alaska-Yukon
border. It is the largest non-polar ice field in the world and shows what much of
the continent would have looked like at the height of the glaciation around 20,000
years ago. Barton et al. (2002) describe this scene as follows:
''Sheets of ice stretch as far as the eye can see, with strange shell-like patterns
scalloped into the surface. Snow clings to mountainsides in great crumbling
chunks while in the glaciers below, ultramarine pools glint in the sunlight. Rivers
run across this glacial landscape and suddenly disappear through the ice to the
valleys below. The ice here is up to 900m deep and the glaciers move up to 200m
a year as they grind and sculpt the landscape around them.''
During the last ice age, glaciers radically changed the north of the continent,
leading to the human invasion of North America through the creation of the
Bering land bridge. At the peak of the last ice age the land bridge was 1,600 km
wide (see Figure 1.4 ). For the first time since the previous ice age (about 100,000
years prior), animals could travel across the land bridge from Siberia into the
North American continent. According to Barton et al. (2002):
''The land bridge was part of a larger ice-free area called Beringia, which