Variability of Inflowing Current Into the Dotson Ice Shelf and Its Cause in the Amundsen Sea

Abstract

The inflow of warm and salty Circumpolar Deep Water affects the melting of the ice shelf on the Amundsen Sea, a significant contributor to global sea level rise. Multi-year mooring data (2014-2016 and 2018-2020) from the front of the Dotson Ice Shelf show the modified Circumpolar Deep Water layer was thicker during 2018-2020 than during 2014-2016. During 2014-2016, Ocean surface stress curl influenced the barotropic process and strengthened southward velocity, while during 2018-2020, it caused lift and downwelling of thermocline depth, increasing the impact of the baroclinic process in ocean circulation. The heat transport to the ice shelf during 2018-2020 (57.42 MW m-1) was half as much as it was during 2014-2016 (111.06 MW m-1) due to a weaker lower layer current. The difference in ocean circulation between two periods, caused by a difference in warm layer thickness, ultimately impacts the heat transport entering the ice shelf cavity. Warm and salty water from the deep ocean flows into the ice shelf cavities in the West Antarctic, causing the ice to melt and contribute to global sea level rise. We measured the current and water properties in front of the Dotson Ice Shelf during 2014-2016 and 2018-2020 and found that the warm layer was thicker during the latter period. Unlike during 2014-2016 when ocean surface stress curl created a spatial imbalance in sea level and affected the southward current due to pressure gradients, during 2018-2020, ocean surface stress curl changed the density by causing upwelling and downwelling. This density change influenced the velocity variation toward the ice shelf. Although the mCDW layer was ticker, the heat influx to the ice shelf during 2018-2020 was half as much as it was during 2014-2016. The difference in ocean current during these two periods, due to differences in the warm layer thickness, ultimately affects how much heat is transported into the ice shelf cavity. The modified circumpolar deep water layer was thicker in 2018-2020 than that during 2014-2016 The baroclinic effect plays a more important role in the variability of the current entering the ice shelf during 2018-2020 Differences in the seasonal cycle of the ocean surface stress curl can affect ocean circulation by changing ocean conditions