Description: Since 2004, several hundreds of diving marine animals, mainly Antarctic and Arctic seals, were fitted with a new generation of Argos-CTD tags developed by the Sea Mammal Research Unit of the University of St. Andrews in Scotland. These tags can be used to investigate simultaneously the at-sea ecology of these animals while collecting valuable oceanographic data. Some of these species are able to travel thousands of kilometres, continuously diving to great depths (590 ± 200 m, with maxima around 2000m). Through the years, these animals have become an essential source of temperature and salinity profiles (MEOP-CTD database available at http://www.meop.net), especially for the polar oceans, complementing efficiently the Argo array. One region where the use of instrumented seals has been particularly successful is the Antarctic continental shelf. Recent contributions to the study of the Antarctic Bottom Water production area near Prydz Bay, the rapidly-thinning ice shelves in Amundsen Bay, or the stratification in the marginal ice zone, are demonstrating the rapidly growing value of these data for Polar Research.

Description: Water mass transformation (WMT) around the Antarctic margin controls Antarctica Bottom Water formation and the abyssal limb of the global meridional overturning circulation, besides mediating ocean-ice shelf exchange, ice sheet stability and its contribution to sea level rise. However, the mechanisms controlling the rate of WMT in the Antarctic shelf are poorly understood due to the lack of observations and the inability of climate models to simulate those mechanisms, particularly beneath the floating ice shelves. We used a circum-Antarctic ocean-ice shelf model to assess the contribution of surface fluxes, mixing, and ocean-ice shelf interaction to the WMT on the continental shelf. The salt budget dominates the WMT rates, with the basal melt of ice shelves driving buoyancy gain at lighter density classes and salt input at coastal polynyas driving buoyancy loss at heavier densities. We found a considerable sensitivity of the WMT rates to model horizontal resolution, tides and topography within the Filchner-Ronne, East and West Antarctica ice shelf cavities. In the Filchner-Ronne Ice Shelf, an anticyclonic circulation in front of the Ronne Depression regulates the rates of basal melting/refreezing and WMT and is substantially affected by tides and model resolution. Model resolution is also found to affect the Antarctic Slope Current in both East and West Antarctica, impacting the on-shelf heat delivery, basal melt and WMT. These results highlight the importance of resolving tides and small-scale features of the flow and topography to adequately represent water mass transformations on the shelf that directly influence the abyssal global overturning circulation.