Page 282 - Earth's Climate Past and Future

258 PART IV • Deglacial Climate Changes

Santa FIGURE 14-7 Millennial fluctuations in the Santa
Barbara 18
Planktic Ice-core Barbara Basin The pattern of δ O changes in planktic
18
18
δ O δ O Basin foraminifera from surface waters of California’s Santa
Cold Warm Cold Warm sediments
18
3 2 1 0 -40 -35 Lam Mixed Barbara Basin (left) closely matches δ O changes in
0
Greenland ice (center). Fluctuations between intervals
of varved sediments in the Santa Barbara Basin and
intervals disturbed by burrowing animals show the
same pattern (right). (Adapted from I. L. Hendy and
J. P. Kennett, “Latest Quaternary North Pacific
10,000
Surface-Water Responses Imply Atmosphere-Driven
Climatic Instability,” Geology 27 [1999]: 291–94.)
Laminated
20,000

Years ago

30,000

40,000

50,000

between pine pollen, indicative of wetter conditions, 14-5 Oscillations in Antarctica
and grass and oak pollen, indicative of dry conditions.
Fluctuations toward wetter conditions in Florida appear The presence of millennial oscillations through much
to correlate with major ice-rafting episodes in the of the northern hemisphere raised the obvious question
North Atlantic. Evidence of millennial fluctuations has of whether or not they were global in extent, and ice
also been found in the northern tropics: fluctuations in cores from Antarctica are an obvious place to look for
the amount of dust delivered to the Arabian Sea, in the an answer. Antarctic ice cores do contain short-term
18
deposition of organic carbon off the coast of Pakistan; δ O oscillations, but they are smaller in size and do not
in the level of North African lakes, and in the abun- have the same timing as those in Greenland ice. Even
dance of plankton in the equatorial Atlantic. though the absolute dating accuracy is insufficient to