CLIMATOLOGY

Ice-Sheet-Driven Shifts

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Science  01 Sep 2000:
Vol. 289, Issue 5484, pp. 1435
DOI: 10.1126/science.289.5484.1435a

Rapid shifts from cold to warm to cold climate, called Dansgaard-Oeschger (D-O) events, occurred during the last glacial period with a periodicity of about 1500 years and culminated in massive discharges of icebergs into the North Atlantic once every 5000 to 10,000 years. These discharges, called Heinrich events, left trails of continental debris on the seafloor that are found mostly between the latitudes of 55,° and 40° N, and are believed to have had a controlling influence on deep water formation in the North Atlantic and thus on global ocean circulation and climate.

Using two deep-sea cores from east of Greenland, van Kreveld et al. assessed the frequency and impact of iceberg production at latitudes north of the main belt of Heinrich debris. They reconstructed surface- and deep-ocean characteristics to show that iceberg production between 46,000 and 22,000 years ago had a periodicity of about 1500 years, like D-O cycles. They also determined how temperature and salinity varied and could be related to changes in ocean stratification and circulation, and how ice rafting events were tied to the surface air temperature changes recorded in Greenland ice. With these data, they construct a detailed relative timeline of a typical 1500-year climate cycle and show how the internal dynamics of the Greenland ice sheet may have acted as the primary pacemaker of the D-O events. — HJS

Paleoceanography15, 425 (2000).

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