Other data sources - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 197

These middens provide valuable evidence of past vegetation because they last for
thousands of years. Additional evidence comes from logs and land snails that
became buried beneath the thick layers of soil that glacial winds spread across the
land. Scientists know from this kind of evidence that the enormous expanse of
grasslands so familiar to us did not exist on the Great Plains during the Ice Age.
White spruce forests covered the plains, although grasses still grew in openings
among the trees'' (Bonnicksen, 2000).

Colinvaux (2007) wrote an extraordinary book detailing 50 years of research
in an attempt to define the climate of the Amazon region during the past Ice Age
based primarily on pollen records and plant fossils. His results suggest that
rainforests continued unabated through the Ice Age but were partly infiltrated by
species normally restricted to higher elevations. This is in contrast to the widely
held belief that aridification converted most rainforests to savannas and that only
smaller pockets of rainforest (refuges) remained through the Ice Age.
Various pollen studies have shown how the various vegetation strata on
mountainsides descended to lower altitudes during ice ages (Andriessen et al.,
1993). In some cases, time series of terrestrial climates were extracted and com-
pared with time series from ocean sediments (e.g., Tzedakis et al., 2006). The
details of these studies are beyond the scope of this topic. Most pollen studies are
relegated to the period since the end of the past Ice Age.

6.5 PHYSICAL INDICATORS

6.5.1 Ice sheet moraines

Moraines (i.e., debris bulldozed into place by the advancing ice sheet front) mark
the perimeter of past ice extent. Marine oxygen isotope records suggest that each
of the great ice ages culminated with roughly the same ice volume (Broecker,
2002). Where moraines from earlier ice maxima are preserved, they support this
interpretation. However, although the location of the southern margins of the
North American and Eurasian ice sheets is clearly defined by moraines, consider-
able uncertainty remains concerning the extent of ice along their northern
perimeters. Based on the extent of moraines, computer simulations of the height
and contour of past ice sheets fitted to these boundaries are only accurate to
about 30%.

6.5.2 Coral terraces

Corals provide a widely used archive to investigate past variations in sea level.
Because many coral species survive only in shallow water, fossil corals found
above or below present reefs preserve indications of past sea levels. As Lambeck
et al. (2002) emphasized,