Indian Ocean and Antarctica were warm during the Younger Dryas. Changes probably were largest around the North Atlantic and probably included reduced export of North Atlantic deep water. Changes into and especially out of the event were very rapid.

ABRUPT CLIMATE CHANGES BEFORE THE YOUNGER DRYAS EVENT

The 110,000-year-long ice-core records from central Greenland (Johnsen et al., 1997; Grootes and Stuiver, 1997) confirmed that the Younger Dryas was one in a long string of large, abrupt, widespread climate changes (Figure 2.5). To a first approximation, the Younger Dryas pattern of change (size, rate, extent) occurred more than 24 times during that interval; additional evidence from marine sediments indicates similar changes over longer times in earlier ice-age cycles (McManus et al., 1998).

Such climate oscillations have a characteristic form consisting of gradual cooling followed by more abrupt cooling, a cold interval, and finally an abrupt warming. Events were most commonly spaced about 1,500 years apart, although spacing of 3,000 or 4,500 years is also observed (Mayewski et al., 1997; Yiou et al., 1997; Alley et al., 2001). The name Dansgaard/ Oeschger oscillation is often applied to such changes on the basis of early work by Dansgaard et al. (1984) and Oeschger et al. (1984). The terminology can be inconsistent; the warm times associated with these during the ice age originally were termed Dansgaard/Oeschger events, but evidence of cyclic behavior suggests that oscillation is more appropriate.

The sequence of Dansgaard/Oeschger oscillations is observed in various records, such as the histories of surface-water temperatures near Bermuda (which were cold when Greenland was cold) (Sachs and Lehman, 1999); oxygenation patterns of the bottom waters in the Santa Barbara basin (which were oxygenated when Greenland was cold) (Behl and Kennett, 1996); wind-blown dust supply to the Arabian Sea (which was dusty when Greenland was cold) (Schulz et al., 1998); and temperature records from the Byrd ice core, West Antarctica (which was warm when Greenland was cold) (Blunier and Brook, 2001). Methane decreased with almost all the Greenland coolings and rose with the warmings, although it changed more slowly than temperature (Chappellaz et al., 1997; Brook et al, 1999; Dällenbach et al., 2000). The colder phases of Dansgaard/Oeschger oscillations in the North Atlantic were marked by increased ice rafting of debris into colder, fresher surface water and by reduction in the strength of



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