Advances in the estimation of surface heat fluxes and thermohaline variability in Terra Nova Bay Polynya - Ross Sea, Antarctica

The Ross Sea is characterized by the presence of persistent ice-free areas during the austral winter (polynyas). One of which is recurrently detected in the coastal area of Terra Nova Bay (TNB) and is important in the modification of the thermohaline structure of the whole Ross Sea. Brine release during sea ice formation increases the salinity of the subsurface water, resulting in the formation of High Salinity Shelf Water (HSSW), the densest water mass of the Southern Ocean. The aim of this study is to investigate the processes that occur in the TNB polynya and the role of the air-sea interactions in the determination of its opening, activity and on the HSSW production that can ventilate the abyssal ocean circulation. First, we analysed the role of the katabatic winds using meteorological data by the Automatic Weather Station Eneide and Rita and ECMWF data, from 1994 to 2015. In the second step the open water fractions from 2005 and 2015, detected by the Ice Surface Temperature (IST) imagery derived from the MODIS data, were used to estimate the opening and the activity of the polynya during the winter season. Then, we estimated the surface heat budget via empirical formulae in the investigated period. During the freezing season, heat flux from the ocean to the atmosphere can be assumed to result directly in ice production considering that ocean column is at its freezing point. Assuming that ice production rate depends on the net heat flux and on the polynya extension, it is possible to calculate the total production of salt released during sea ice formation and HSSW volume. The HSSW production results switched from the lowest values during the first years of the investigated period to the highest values for the last period. Finally a comparison between the estimated HSSW production and the salinity observed within the TNB water column show similar tendency in the last years after 2002, while during the period 1995-1998 the behaviour is different. Our results could be explained by a different contribution of the Circumpolar Deep Water inflow and HSSW production in the TNB area.