Calibration of Na partitioning in the calcitic foraminifer Operculina ammonoides under variable Ca concentration: Toward reconstructing past seawater composition

Reconstructions of past changes in the seawater calcium concentration (Casw) are critical for understanding the long-term changes in ocean chemistry, the carbon cycle and for accurate application of elemental proxies (El/CaCaCO3) in foraminifera (e.g., Mg/Ca as proxy of temperature). Here we show that Na/Ca ratios in foraminiferal shells could be used for reconstructing Casw and Mg/Ca in the past oceans. Ca has a short residence time in the...