OCEANS: Tracing Ocean Circulation

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Science  23 Jun 2000:
Vol. 288, Issue 5474, pp. 2097e-2099
DOI: 10.1126/science.288.5474.2097e

Understanding past climate depends, to a large extent, on understanding the circulation of oceanic deep water masses because the atmosphere contains so much less mass and heat than the oceans and because most of the oceans are deep water. One way to study deep ocean paleocirculation is to measure the distribution of nutrient tracers contained in the shells of benthic foraminifera; the deep water masses in which these forams grow have many distinctive chemical and physical characteristics that are reflected in the composition of their calcium carbonate skeletons. However, different tracers can give conflicting results.

Marchitto et al. have identified a promising new proxy, Zn. Their measurements of Zn/Ca in two taxa of Holocene benthic foraminifera show that the ratio mirrors that of the bottom water where the forams grow. They suggest that Zn/Ca, used in conjunction with data on Cd/Ca (another deep water tracer), may be useful in solving one of the central puzzles in oceanography and paleoclimatology: how the carbonate ion concentration of the ocean has varied in the past.—HJS

Paleoceanography 15, 299 (2000).

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