Reconsidering Coral Paleothermometers

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Science  17 Mar 2000:
Vol. 287, Issue 5460, pp. 1889
DOI: 10.1126/science.287.5460.1889f

One method of estimating sea surface temperatures across glacial cycles during the Quaternary relies on the measurement of the ratio of Sr to Ca in the aragonite skeletons of coral. Studies of modern corals have shown that this ratio has a simple thermodynamic dependence. The accuracy of this proxy for temperature depends on the assumption that the Sr/Ca of sea water has been constant over the relatively short time scales of these cycles, which is based on the oceanic residence times of Ca and Sr of about one and five million years, respectively.

This assumption may not be correct—Martin et al. have found coincident variations in the Sr/Ca of planktonic and benthic foraminifera from the Pacific and Atlantic basins over the past three hundred thousand years. They suggest these variations were caused by changes in the Sr/Ca of sea water, and not by temperature. This would mean that coral Sr paleothermometry has overestimated the temperature increase of the surface ocean during glacial to interglacial transitions.—HJS

Geochem. Geophys. Geosys.1, paper 1999GC000006 (1999).

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