Other data sources - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 196

Figure 6.7. (Upper panel) d 18 O from GRIP in Greenland. (Lower panel) Measured

susceptibility of lake sediments in France.

plants and how easily they are transported by wind or by animals. Wilson et al.
(2000) provided data from a site that was a former lake in the United Kingdom.
A sediment core revealed that, prior to about 9,600 ybp , the only trees were birch,
with few willow and juniper. Birch pollen probably indicates tundra (mostly dwarf
birch). There was also sedge, grass, and herb pollen. Starting around 9,600 ybp ,a
series of sharp changes occurred in the pollen record. First, the number of birches
increased sharply. They were subsequently replaced by Scotch pine, which were in
turn replaced by hazel and bog myrtle. Soon thereafter, there was great diversifica-
tion into elm, oak, and many other species of trees as the climate warmed. Even
lime pollen was found:

''Fossil pollen is especially useful in determining the number of different
kinds of trees, shrubs, and other plants that grew around a pond when each
layer formed. The core samples that scientists take from the bottom of these
ponds capture this record in long cylinders of mud. Then scientists date each
layer using radiocarbon methods and identify and count the fossilized pollen
grains. Thus, the ooze at the bottom of a pond can provide the key to unlocking
the ancient history of a forest. Scientists reconstructed the vegetation that grew
on the Great Plains and elsewhere during the Ice Age using fossil pollen and
macrofossils, or fossilized plant parts such as seeds, needles, cones, wood, and
twigs. Much of this evidence comes from cores, but plant parts also accumulate
in pack rat dens, glued together with their droppings into a mass called a midden.