Life and climate in an ice age - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 13

dislodging soils and relatively unconsolidated sedimentary rocks. The weight of
the ice sheets provides a pressure force that uses debris carried in the bottom layer
of ice to grind and gouge out small pieces of even the hardest bedrock. In areas
where basal layers of ice alternately freeze and thaw through time, water trickles
down into cracks in bedrock when the ice melts and then expands when it freezes
again, breaking off large chunks of bedrock. This freeze-thaw process quarries
large slabs of bedrock and incorporates them in the ice for further grinding and
fragmentation. These and other processes at work in ice sheets erode huge
volumes of bedrock debris in all sizes. The ice sheets carry this material out
toward their margins and deposit it along their edges, where the ice melts

.
Winds then rework these deposits, creating a gradation of grains away from ice
margins. The coarsest debris remains in place but strong winds can transport
medium to fine sand over short distances. Winds also lift and carry finer silt-sized
sediment farther from source regions

...

. Winds can carry even finer (clay-sized)
dust completely around the world. Glacial-age layers in the Greenland ice sheet
contain ten times as much fine dust as interglacial layers. Chemical analysis of
this dust indicates that the main source region was Asia rather than nearby
North America. Dust transport was also greater at lower latitudes during the
LGM.''

...

Ruddiman (2007) also said:

''Despite the harshness of this environment, the steppe and tundra supported
a diverse population of large mammals, including woolly mammoths and
rhinoceroses. It is not clear how the creatures found enough food to survive
during the cold winters.''

Ruddiman discussed at length the conflicting views on the climate in the
tropics during the LGM. CLIMAP (Climate Long-range Investigation, Mapping,
and Prediction) results from ocean sediments indicated that tropical oceans were
just 1 to 2 C cooler than today, with a few regions in the Pacific being slightly
warmer than today. However, other data suggest much cooler temperatures.
Tropical mountain glaciers descended 600 to 1,000 meters, indicating a tempera-
ture drop of 4 to 6 C. Tropical vegetation on the flanks of mountains also
indicates a larger temperature drop during the LGM. Ruddiman went on to
discuss the pros and cons of both sides of the controversy, and concluded that
perhaps the ''truth lies somewhere in the middle''.
Mix et al. (2001) discussed the terminal climate during the LGM about 20,000
years ago when the ice sheets of the last ice age reached their maximum. As they
pointed out, the LGM is important because (as they stated):

. The LGM represents a global climate state dramatically different from that of

today, and thus provides a useful test of climate models' sensitivity to change.

. The LGM is reasonably close to an equilibrium state of climate (to the extent that

equilibrium is ever obtained in the recent geologic past).