Fossil shells of planktonic foraminifera in ocean sediments can be used to estimate the temperature and salinity of the waters in which they once grew. We use paired oxygen isotopic and Mg/Ca analyses of coretop shells of G. ruber (live specimen at right) for a transect of cores in the Atlantic basin that captures the full ocean basin gradients of temperature and salinity. Our data demonstrate that this approach provides reliable estimates of modern surface ocean properties and thus can be used to estimate changes in past oceans.
Arbuszewski, J.A., deMenocal, P.B., Kaplan, A., Farmer, E.C. On the fidelity of shell-derived d18Oseawater estimates. Earth and Planet. Sci. Lett., doi:10.1016/j.epsl. 2010.10.0