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CHAPTER 14 • Millennial Oscillations of Climate 257

European European FIGURE 14-6 Millennial-scale
Ice core soil properties pollen climate changes in Europe Similar to
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δ 0(‰) Poor in Rich in Cold Warm δ O changes in Greenland ice (left),
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Cold Warm clay and clay and 100% 100% millennial-scale fluctuations occur in
–40 –35 carbon carbon Herbs Trees
European soils (center) and pollen
(right). (Left: Adapted from P. Grootes
10,000 4 et al., “Comparison of Oxygen Isotope
Records from the GISP and GRIP
20,000 Greenland Ice Cores,” Nature 366 [1993]:
6 552–54. Center: Adapted from N.
30,000
Thouveny et al., “Climate Variations in
Years ago 40,000 8 Depth in core (m) Europe over the Past 140 Kyr Deduced
from Rock Magnetism,” Nature 371
[1994]: 503–6. Right: Adapted from G. M.
50,000
Woillard and W. G. Mook, “Carbon–14
10
60,000 Dates at Grande Pile: Correlation of Land
and Sea Chronologies,” Science 215 [1982]:
70,000 159–61.)
12
80,000

Greenland and colder temperatures in the North Atlantic absent from the deep basin during warmer climates
Ocean. to prevent small creatures from burrowing and churn-
Short-term fluctuations have also been discovered ing these delicate layers. Sediment mixing occurred
in the glacial sections of windblown loess deposits in during the oscillations toward colder climates, indicat-
China. Coarse loess-rich layers that indicate physical ing that burrowing activity was vigorous. The obvious
weathering during very cold intervals alternate with match in pattern between the records in the Santa Bar-
finer, clay-rich soils that indicate greater chemical bara Basin and those in Greenland ice makes it clear
weathering during warm episodes. Although the Asian that very similar millennial oscillations affected both
soil/loess sequences are not well dated, changes in that regions.
region may also match oscillations in and around the Other indications of millennial-scale oscillations in
North Atlantic. western North America come from fluctuations of
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Other climate scientists have also found millennial glacial Lake Bonneville in Utah: the younger C-dated
oscillations in regions far from the North Atlantic lake level maxima appear to correlate with major ice-
Ocean. In the Santa Barbara Basin along the Pacific rafting events in the North Atlantic. Also, millennial-
coast of North America at 35°N, several climatic signals scale advances of mountain glaciers have been found in
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match the δ O fluctuations in the Greenland ice sheet the Sierra Nevada of California, the Cascades of
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(Figure 14–7). Short-term oscillations in δ O values Oregon and Washington, and the Colorado Rockies. In
measured in the shells of planktic foraminifera indicate the United States Midwest, far from the Atlantic mar-
large (4°C or more) temperature changes in near- gins of the Laurentide ice sheet, several ice lobes appear
surface waters. In addition, the type of sediment to have fluctuated in rough synchrony with the larger
deposited in the Santa Barbara Basin fluctuates between ice-rafting episodes, hinting at a possible link between
layers mixed by burrowing animals and intervals with the land and ocean margins. A pollen record from
varvelike layering still intact. Oxygen must have been Florida also shows fluctuations during the last glaciation