Mg/Ca and Sr/Ca Paleothermometry from Calcareous Marine Fossils

Due to its large heat storage capacity and importance in equator-to-pole heat transport, the ocean plays a fundamental role in the evolution of Earth's climate. Accordingly, the distribution of sea surface and bottom water temperature (BWT) and salinity is perhaps the best representation of the state of the climate system, both past and present. This article discusses four important paleotemperature proxies, namely Mg/Ca in planktonic foraminifera and Sr/Ca in corals as recorders of sea surface temperatures and Mg/Ca in benthic foraminifera and ostracodes as proxies of BWTs. A clear advantage of these carbonate-based thermometers is that coupling δ¹⁸O and Mg/Ca measurements in foraminifera or Sr/Ca in corals provides a novel way to adjust for the temperature dependency of δ¹⁸O and isolate the record of δ¹⁸O_sw. This can then be used to reconstruct local changes in the evaporation-precipitation balance (and by inference salinity) or the advection of water of different δ¹⁸O_sw and provide valuable information about changes in continental ice volume.