indicate enhanced nutrient upwelling and thus higher productivity caused by increased trade wind strength during the Younger Dryas (Hughen et al., 1996), or decreased riverine runoff from adjacent land masses (Peterson et al., 2000).

In the last decade, substantial paleooceanographic oscillations correlated with the Younger Dryas have been documented from as far away as the North Pacific. In the Santa Barbara Basin (Kennett and Ingram, 1995) and the Gulf of California (Keigwin and Jones, 1990), sediments that are normally anoxic became oxic during the Younger Dryas. Evidence of rapid climate variability in the northwestern Pacific over the last 95,000 years has been observed (Kotilainen and Shackleton, 1995). Even the eastern equatorial Pacific has yielded a Younger Dryas event determined from δ18O and δ13C records (Koutavas and Lynch-Steiglitz, 1999).

In the North Arabian Sea and Indian Ocean, high-frequency climate variability linked to events in the Northern Hemisphere has also been demonstrated (Schulz et al., 1998). Off the coast of Africa at Ocean Drilling Program Site 658, an arid period corresponding to the Younger Dryas punctuated a longer humid period (deMenocal et al., 2000a). Between 20°N and 20°S, Younger Dryas cooling is observed on the basis of alkenone paleothermometry (Bard et al., 1997). In a sediment record that links land to ocean, Maslin and Burns (2000) documented evidence of a dry Younger Dryas in the tropical Atlantic Amazon Fan. As reviewed by Boyle (2000), work including that by Boyle and Keigwin (1987) and Bond et al. (1997) showed that changes in proxies from bottom-dwelling foraminiferal shells indicate reduction in deep export of waters that sank in the North Atlantic during the Younger Dryas. Alley and Clark (1999) reviewed evidence from several marine cores that show warmth during the Younger Dyras in the southern Atlantic and Indian Oceans, opposite to most global anomalies but consistent with the warmth indicated in most Antarctic ice cores at that time (Steig et al., 1998; Bender et al., 1999; Blunier and Brook, 2001).

Overall, the available data indicate that the Younger Dryas was a strong event with a global footprint. Available data are not sufficient to identify the climate anomaly everywhere, and further understanding almost certainly will require more data. Different paleoclimatic recorders respond to different aspects of the climate system with different time resolution, so it is not surprising that the picture is not perfectly clear. Broadly, however, the Younger Dryas was a cold, dry, and windy time in much of the world although with locally wetter regions probably linked to storm-track shifts. The far southern Atlantic and many regions downwind in the southern

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement