Improving past sea surface temperature estimates based on planktonic fossil faunas

A new method of past sea surface temperature (SST) reconstruction based on the modem analog technique (Prell, 1985) and on the indirect approach (Bartlein et al., 1986) has been developed: the revised analog method (RAM). Applied to planktonic foraminifera, this technique leads to significant improvements in modern SST reconstruction with respect to former methods: our estimates are characterized by much lower residuals and a better coverage of the observed SST range. Moreover, the error of RAM estimates of past SSTs is lower than that associated with former reconstructions, particularly at middle and high latitudes. In low latitudes, cold season SSTs reconstructed by RAM during glacials are 1 degrees-3 degrees C lower than previously estimated. Our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics.