Extending the SST gradient into the Arctic: Paleoclimate evidence and future climate implications

The most recent geologic interval characterized by surface temperatures similar to those projected for the end of this century occurred about 3.3 to 3.0 Ma, during the mid-Piacenzian Age of the Pliocene Epoch. Climate reconstructions of this warm period are integral to understanding both past warm climate equilibria and to predicting responses to today's transient climate. The Arctic Ocean is of particular interest because in this region climate proxies are rare, and climate models struggle to predict climate sensitivity and the response of sea ice. In order to provide the first quantitative climate data from this region during this interval, we estimated sea surface temperatures (SST) from Ocean Drilling Program Sites 907 and 909 in the Nordic Seas and from Site 911 in the Arctic Ocean based on Mg/Ca of Neogloboquadrina pachyderma (sinistrally coiled) and alkenone unsaturation indices. SST estimates indicate much warmer than modern conditions in the Arctic Ocean with temperatures as high as 18°C. SST anomalies (mid-Piacenzian minus modern) increase with latitude across the North Atlantic and into the Arctic, extending and confirming the reduced mid- Piacenzian pole-to-equator temperature gradient. The agreement between proxies and with previously documented qualitative assessments of intense warming in this region corroborate a poleward transport of heat and at least seasonally ice-free Arctic, conditions that may serve as a possible analog to future climate if the current rate of Arctic sea-ice reduction continues.