Climate Science

A Constant Conveyor

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Science  07 May 2004:
Vol. 304, Issue 5672, pp. 797
DOI: 10.1126/science.304.5672.797c

One of the most commonly accepted views of the relation between climate and ocean circulation is known popularly as the “global conveyer,” meaning that deep water forms in the North Atlantic Ocean in large amounts during interglacial periods and in smaller volumes during glacial intervals, producing significant changes in the rate of large-scale ocean circulation. Much of the evidence for this belief is based on studies of the carbon isotopic composition of benthic foraminifera, i.e., those that lived on the sea floor over the last glacial/interglacial cycle.

Raymo et al. examine this proposition in more detail by comparing and contrasting carbon isotopic profiles from seven sites in the North Atlantic covering the last 27 glacial cycles, a time span of nearly 2 million years. They suggest that the production rate of North Atlantic Deep Water (NADW), the motive force behind the global conveyer, has not varied significantly on glacial time scales during most of that interval, despite dramatic differences in climate state and ice volume. Instead, they propose (i) that the variability of NADW production observed over the last deglaciation is not typical, (ii) that the carbon isotopic signature in the region where much of the NADW originates is unusual during this anomalously warm interglacial period, and (iii) that this possibility must be considered when using benthic carbon isotopic records to infer past ocean circulation changes. — HJS

Paleoceanography 19,10.1029/2003PA000921 (2004).

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