Mg/Ca paleothermometry in high salinity environments

• Published in: Earth and Planetary Science Letters
• Main Authors: Hoogakker, B.A.A., Klinkhammer, G, Elderfield, H, Rohling, Eelco, Hayward, Chris
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier
• Subjects: Keywords: CaCO3 supersaturation; conventional ICP-AES; electron microprobe analysis; flow-through time resolved analysis; Globigerinoides ruber; high Mg-calcite overgrowths; Mg/Ca paleothermometry; Red Sea; salinity; Atomic emission spectroscopy; Calcite; Carbonate CaCO3 supersaturation; scanning electron microscopy; Planktonic foraminifera
• Online Access: http://hdl.handle.net/1885/80029; https://doi.org/10.1016/j.epsl.2009.05.027; https://openresearch-repository.anu.edu.au/bitstream/1885/80029/5/Rohling_E_2009_MgCa_paleothermometry.pdf.jpg; https://openresearch-repository.anu.edu.au/bitstream/1885/80029/7/01_Hoogakker_Mg%2FCa_paleothermometry_in_high_2009.pdf.jpg

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.