Page 241 - Earth's Climate Past and Future

CHAPTER 12 • Last Glacial Maximum 217

FIGURE 12-7 Pollen distributions and climate Today the distribution of pollen in
80 the northern midwestern United States reflects control by (A) precipitation and
60 (B) temperature. (C) Prairie grasses and herbs are most abundant where rainfall is low,
and tree pollen is more common in wetter eastern regions. (D) Spruce trees proliferate
in the colder north, (E) oak in the warmer south. (Adapted from T. Webb III, “Holocene
Palynology and Climate,” in Paleoclimate Analysis and Modeling, ed. A. Hecht [New York: Wiley,
80
1985].)
60
A Annual precipitation (cm)

Mean July temperature (°C) 15
2 30
2 25 Spruce pollen

6 20
6

10 10
5
B Annual temperature (°C) 0
0 500 1000 1500
20 Annual precipitation (mm)
40

40 20

C Prairie pollen (%)

20 50

Mean July temperature (°C) 10
25
20
D Spruce pollen (%) 30
15

Oak pollen
Prairie pollen
0
20 5 0 500 1000 1500 0 500 1000 1500
Annual precipitation (mm)
40
20 FIGURE 12-8 Pollen percentages and climate The
40
abundances of spruce, oak, and prairie pollen follow distinct
E Oak pollen (%) temperature and precipitation patterns. Colors indicate the
same pollen abundances as in Figure 12-7. (Adapted from
T. Webb III et al., “Climatic Change in Eastern North America
During the Past 18,000 Years: Comparisons of Pollen Data with
Model Results,” in North America and Adjacent Oceans During the Last
Deglaciation, ed. W. F. Ruddiman and H. E. Wright [Boulder, CO:
Geological Society of America, 1987].)