Sea surface salinity reconstruction as seen with foraminifera shells: Methods and cases studies

Abstract

Reconstruction of past salinities in surface oceans (SSS) can be done by measuring the isotopic composition of foraminifera shells found in the deep sea sediments. The proportion of heavy oxygen isotopes (18O) in the calcite of these shells depend on the temperature and the isotopic oxygen composition of the surrounded waters (δ18 Osw), this latter parameter depending on the water salinity. Mainly two equations allows to reconstructed past SSS, one estimating past temperature variations and the other one changes in the δ18 Osw through time. Uncertainties linked with these calculation can be important, and therefore quantitative reconstructions need to be taken with cautions. For some specific cases, uncertainties on temperature and δ18 Osw estimations can be reduced. For such cases, salinity reconstructions showing amplitude changes higher than 1 per mil can be considered as significative.