Mg/Ca paleothermometry in high salinity environments

• Published in: Earth and Planetary Science Letters
• Main Authors: Hoogakker, Babette A.A., Klinkhammer, Gary P., Elderfield, Harry, Rohling, Eelco J., Hayward, Chris
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2009
• Subjects: Planktonic foraminifera
• Online Access: https://eprints.soton.ac.uk/67394/

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.