Mg/Ca paleothermometry in high salinity environments

Hoogakker, Babette A.A., Klinkhammer, Gary P., Elderfield, Harry, Rohling, Eelco J. and Hayward, Chris (2009) Mg/Ca paleothermometry in high salinity environments. Earth and Planetary Science Letters, 284 (3-4), 583-589. (doi:10.1016/j.epsl.2009.05.027).

Abstract

Planktonic foraminiferal Mg/Ca ratios have become a fundamental temperature proxy in past climate reconstructions. However, in the highly evaporative seas of the tropics and subtropics, anomalously high planktonic foraminiferal Mg/Ca ratios arise, possibly linked to high salinities. The extent to which salinity affects Mg uptake into foraminiferal calcite remains disputed. Some studies suggest only minor salinity effects, whereas others suggest a dominant role. Here, we present new data from the highly saline (> 40) Red Sea, which separate pure foraminiferal calcite from other phases. The results show that high Mg/Ca ratios (7 to 13 mmol/mol), found by conventional analysis of planktonic foraminifera from a Red Sea sediment core, are not caused by increased Mg uptake into foraminiferal calcite in a high salinity setting (e.g. beyond those predicted by culturing studies), but instead result from secondary high Mg-calcite overgrowths. The overgrowths likely formed near the sediment–seawater interface, from CaCO3 supersaturated interstitial seawater.

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Contributors

Author: Eelco J. Rohling

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