The role of the deep ocean in North Atlantic climate change between 70 and 130 kyr ago
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THE suggestion(1) that changes in North Atlantic Deep Water (NADW) production are linked through surface heat flux to the atmospheric temperature over Greenland is supported by earlier indications(2,3) that NADW production decreased during glacial times, and by the subsequent finding(4-6) that it declined during the Younger Dryas cool period at the end of the last glaciation. Changes in North Atlantic surface temperatures have been found? to mirror high-frequency temperature changes recorded in Greenland ice cores over the past 80 kyr, but the connection to abyssal circulation has yet to be established, except for one or two isolated oscillations(8,9). Here we present carbon and oxygen isotope analyses of benthic foraminifera in a high-resolution North Atlantic deepsea sediment core for the period 70-130 kyr ago. These data allow us to reconstruct the history of NADW production, which shows a close correlation with Greenland climate variability for much of this time interval, suggesting that the climate influence of NADW variability was widespread. We see no evidence, however, for changes in NADW production during substage 5e (the Eemian interglacial period), in contrast with recent ice-core data(10) which suggest severe climate instability in Greenland during this time period. Our results may support suggestions, based on data from a second ice core, that this apparent instability is am artefact caused by ice flow(11). Alternatively, the Eemian climate instability may have had a different origin from the subsequent climate events.