Distribution of modified Circumpolar Deep Water and its threat in Vincennes Bay, East Antarctica

The Antarctic Bottom Water formation site Vincennes Bay, East Antarctica is experiencing a substantial intrusion of modified Circumpolar Deep Water (mCDW), which may inhibit the formation of Dense Shelf Water (DSW) and drive basal melting of the ice shelves. Based on hydrographic data obtained from March to November in 2012, we evaluated the spatial spread of mCDW over the continental shelf region of Vincennes Bay and the associated temporal evolution of water properties, as well as the sea ice formation effect on water column in the coastal polynya. Results show that two branches of mCDW occupied the deep layers of the continental shelf, distinguished by the potential density (smaller than 27.8 kg/m3 or not) when potential temperature theta=-0.5 degrees C in the theta-salinity space. The warmer and less dense branch observed on the east plateau, accessed the eastern ice shelves in the coastal polynya to drive basal melting of ice shelves. In contrast, the other colder and denser branch in the mid-depression reached the western Underwood Ice Shelf. DSW formation was detectable in the coastal polynya during September-November, proving the occurrence of deep convection. Surface heat loss and brine rejection during the intensive sea ice formation contributed to the destratification of the water column in the coastal polynya. It was estimated that at least 1.11 +/- 0.79 TW heat carried by mCDW into the inner part of the polynya.