NOAA/WDS Paleoclimatology - Weddell Sea ODP690 Paleocene-Eocene Thermal Maximum Mg/Ca and d18O Data

Earth's hydrological cycle was profoundly perturbed by massive carbon emissions during an ancient (56 Ma) global warming event referred to as the Paleocene-Eocene thermal maximum (PETM). One approach to gaining valuable insight into the response of the hydrological cycle is to construct sea-surface salinity (SSS) records that can be used to gauge changes in the rates of evaporation and precipitation during the PETM in such climatically sensitive areas as the circum-Antarctic region. Here, we pair oxygen isotope (δ18O) and magnesium-calcium (Mg/Ca) measurements to reconstruct PETM sea-surface temperatures (SSTs) and δ18O composition of seawater (δ18Osw) at austral Site 690 (Weddell Sea). Several discrepancies emerge between the δ18O- and Mg/Ca-based SST records, with the latter indicating that the earliest PETM was punctuated by a short-lived ~4°C increase in local SSTs. Conversion of the δ18Osw values to SSS reveals a ~4 ppt decrease ~50 ka after peak PETM warming at Site 690. This negative SSS (δ18Osw) anomaly coincides with a prominent minimum in the planktic foraminifer δ18O record published for the Site 690 PETM section. Thus, our revised interpretation posits that this δ18O minimum signals a decrease in surface-ocean δ18Osw fostered by a transient increase in mean annual precipitation in the Weddell Sea region. The results of this study corroborate the view that the poleward flux of atmospheric moisture temporarily increased during a distinctive stage of the PETM.