that caused the collapse of the Classic Mayan civilization. Black et al. (1999) demonstrated that decadal-to-multicentury variations in wind-driven upwelling in the Cariaco Basin, and by inference the mean position of the ITCZ, were closely linked to North Atlantic SSTs over the past eight centuries. Other records from upwelling areas off Pakistan (e.g., von Rad et al. 1999) and zones of layered sediment deposited under anoxic conditions—such as fjords along the coast of British Columbia, Canada—also possess marine sediments with distinct seasonal layers that offer high-resolution histories of late Holocene climate.

Records from rapidly accumulating sediments in the Atlantic Ocean also provide information about temperature changes over the last 2,000 years. The temperature proxies derived from benthic and planktic foraminifera in the northwestern Atlantic Ocean (Keigwin and Pickart 1999, Marchitto and deMenocal 2003), the Bermuda Rise (Keigwin 1996, Keigwin and Boyle 2000), and off the west coast of Africa (deMenocal et al. 2000), as well as from marine diatoms (silica-shelled algae; Jiang et al. 2002), all reveal changes in surface ocean temperatures or surface ocean temperatures transmitted to depth by sinking water masses. To varying degrees, both the Little Ice Age and the warm period around medieval times are revealed by these records (Figures 5-4 and 5-5). It has been suggested that Holocene climate variations indicated by peaks in ice-

FIGURE 5-4 Variation of bottom temperature on the Labrador current inferred from Mg/Ca ratios in forams and the relation to the measure of ice-rafted debris (IRD) showing variations in North Atlantic temperature changes as reflected in deep-sea sediments. SOURCE: Marchitto and deMenocal (2003). Reproduced by permission of American Geophysical Union; copyright 2003.



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