Late Pliocene Atlantic surface water pulses precede enhanced deeper water inflow and stratification in the Fram Strait

Enhanced northward heat transport via Atlantic water is driving Arctic Atlantification, but it is unclear how it will contribute to warming, sea-ice melt, and stratification changes in a warmer climate. Here, we present a new Late Pliocene record (ca. 3.4−3.0 Ma) of surface water mass changes from Ocean Drilling Program Site 910 based on marine palynomorphs from the Fram Strait, focusing on the mid-Piacenzian warm period (3.264−3.025 Ma), the most recent geological time interval with warmer-than-present climate. Our record shows predominantly polar surface waters in the Fram Strait, interrupted by two distinct pulses of Atlantic-sourced waters. These pulses are followed by a strongly stratified water column, with enhanced inflow of deeper Atlantic waters underneath a sea-ice−covered, fresher surface layer. Thus, future Arctic Atlantification may lead to a long-term strengthening of stratification as enhanced northward oceanic heat transport is counterbalanced by surface-layer freshening driven by sea-ice melting. The strong stratification may isolate deeper warm Atlantic water from direct ocean-atmosphere heat and moisture exchanges, potentially slowing sea-ice loss.