Tropical forcing of Circumpolar Deep Water Inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica

Outlet glaciers draining the Antarctic Ice Sheet into the Amundsen Sea 1 Embayment (ASE) have accelerated in recent decades, most likely as a result of increased 2 melting of their ice shelf termini by warm Circumpolar Deep Water (CDW). An ocean 3 model forced with climate reanalysis data shows that, beginning in the early 1990s, an 4 increase in westerly wind stress over the continental shelf edge drove an increase in 5 CDW inflow onto the shelf. The change in local wind stress occurred predominantly in 6 fall and early winter, associated with anomalous high sea level pressure (SLP) to the 7 north of the ASE and an increase in sea surface temperature in the central tropical Pacific. 8 The SLP change is associated with geopotential height anomalies in the middle and upper 9 troposphere, characteristic of a stationary Rossby wave response to tropical SST forcing, 10 rather than with changes in the zonally symmetric circulation. Tropical Pacific warming 11 similar to that of the 1990s occurred in the 1940s, and thus is a candidate for initiating the 12 current period of ASE glacier retreat. Further warming of the tropical Pacific can be 13 expected to contribute to continued CDW inflow and continued melting of ASE outlet 14 glaciers. 15