Chapter Nineteen Elemental Proxies for Reconstructing Cenozoic Seawater Paleotemperatures from Calcareous Fossils

Abstract

Publisher Summary This chapter discusses the elemental proxies for reconstructing cenozoic seawater paleotemperatures from calcareous fossils. Oxygen isotope (δ18O) measurements in foraminifera, the standard tool in paleoceanography, have provided seminal information about the evolution of Cenozoic climate. However, their dependence on both temperature and the isotopic composition of the water — the δ18O of seawater (δ18O water) on both the extent of continental ice sheets and the local salinity — limits their utility for reconstructing past ocean temperatures, and hence the need for independent proxies for temperature. Elemental ratios in biogenic carbonates are particularly useful as they are measured on the same phase as δ18O and thus reduce the uncertainties associated with the use of different proxy carriers. It has been realized that magnesium (Mg) and strontium (Sr) have potential for reconstructing ocean paleotemperatures. Among the new elemental proxies are Mg/Ca in planktonic foraminifera and Sr/Ca in corals as recorders of sea surface temperatures (SSTs) and Mg/Ca in benthic foraminifera and ostracodes as proxies of bottom water temperatures. A clear advantage of these carbonate-based thermometers is that coupling δ18O and Mg/Ca measurements in foraminifera or Sr/Ca in corals, provides potentially a novel way to adjust for the temperature-dependency of δ18O and isolate the record of δ18Owater, which can then be used to reconstruct local changes in evaporation–precipitation (and by inference salinity) and provide valuable information about changes in continental ice volume.