Mg/Ca paleothermometry in high salinity environments

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 wh...

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Bibliographic Details
Published in:	Earth and planetary science letters 2009-07, Vol.284 (3), p.583-589
Main Authors:	Hoogakker, Babette A.A., Klinkhammer, Gary P., Elderfield, Harry, Rohling, Eelco J., Hayward, Chris
Format:	Article
Language:	eng
Subjects:	CaCO3 supersaturation Calcite Calcium carbonate conventional ICP-AES electron microprobe analysis Evaporative flow-through time resolved analysis Globigerinoides ruber high Mg-calcite overgrowths Magnesium Marine Mg/Ca paleothermometry Reconstruction Red Sea Salinity scanning electron microscopy Uptakes
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Summary:	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 CaCO 3 supersaturated interstitial seawater.
ISSN:	0012-821X 1385-013X