On the warm inflow at the eastern boundary of the Weddell Gyre

Abstract

The Weddell Sea plays an important role for the global oceans and climate by being one of the biggest production and export areas of Antarctic Bottom Water (AABW). Circumpolar Deep Water (CDW) enters the Weddell Gyre (WG) at its eastern boundary. Then called Warm Deep Water (WDW), it is a major contributor to the formation of deep and bottom waters due to ocean-ice shelf interactions in the southern and soutwestern Weddell Sea. Hydrographic data collected between 0 and 30°E on the RV Polarstern cruise ANT XX/2 reveals a two-core structure for the eastern inflow of warm water at roughly 20°E but not further downstream at the Greenwich meridian (GM). Model results and climatological fields suggest that the two cores represent two separate modes of warm inflow. One mode is driven by eddy mixing in the northeastern corner of the WG and the other one is an advective mode, forming the southern branch of the inflow which extends beyond 30°E before turning westward. Both pathways are likely to carry waters from different origins within the Antarctic Circumpolar Current ACC, where more ventilated CDW is found at the Southern Boundary SB compared to the centre. The southern route shows considerable interannual variability in the model. A variable inflow of two types of CDW together with admixed recirculated and cooler waters from the Weddell Sea can potentially contribute to the observed variability and warming trend of WDW over the last decade at the GM.