Warm Weddell Deep Water west of Maud Rise

Abstract

A pool of relatively warm (>1.0°C) Weddell Deep Water (WDW) immediately west of Maud Rise appears to be a quasi‐stationary feature. The “warm pool” is derived from the flow of warm WDW around the flanks of Maud Rise. An austral spring 1989 expedition of the R/V Akademik Fedorov obtained detailed measurements of the warm pool. It displays the general regional relationship of temperature maximum (t‐max) warmth to shallowness of the pycnocline, as well as mixed layer oxygen concentration well below full saturation. Depression of oxygen values is a product of injection of WDW into the mixed layer during the ice‐covered winter period. Associated with this transfer are high vertical fluxes of heat and salt which limit the thickness of the sea ice cover. In the winter the atmosphere is sufficiently cold to remove the WDW heat without massive sea ice melting, though the regional ice thickness is restricted. In the spring the atmospheric conditions cannot remove the ocean heat, and ice melting ensues before the atmospheric heat budget alone can account for the ice melt. This is clearly seen in the warm pool as very low mixed layer oxygen, which is a reflection of high WDW entrainment and vertical heat flux and is normally associated with high mixed layer salinity. Here it is coupled instead with reduced salinity, a result of approximately 0.5 m of ice melt. The Fedorov data confirm the role of oceanic heat flux in early removal of Southern Ocean sea ice at the end of winter, in that the region of highest WDW entertainment is associated with greater amounts of melt water.