Wintertime oceanography of the Adélie Depression

The formation of high-salinity shelf waters beneath coastal polynyas from enhanced sea-ice production and brine rejection during wintertime is critical to the production of Antarctic Bottom Waters. We report on the first wintertime measurements of high-salinity shelf water formation over the Adélie Depression off the East Antarctic coast between 143° and 146°E, during the Mertz Glacier Polynya Experiment in July–August 1999. The general circulation and evolution of water masses in the Adélie Depression during winter are described, and in particular we quantify the rates of brine rejection (sea-ice growth), ocean heat flux, and latent heat flux, in the Mertz polynya central to the formation of high-salinity shelf waters. We find shelf waters above the minimum sill depth with sufficient density to become Adélie Land Bottom Water and suggest the highest production rates occur near Commonwealth Bay. Sea-ice growth and heat transfer rates are calculated from the divergence of heat and freshwater fields around a closed volume beneath the Mertz polynya. The sea-ice growth estimates and associated Monte Carlo errors are found to range from 4.8±1.7, 4.1±1.5, 8.4±1.7 cm d−1, respectively, over a 3-week period. The average growth rate is 5.8 cm d−1. Near the Mertz polynya the sensible heat from ocean transport is between 15±6 and 43±11 W m−2, with an average of 30 W m−2, and the latent heat budget is between 125±45 and 254±52 W m−2, with an average of 174 W m−2. We conclude that during winter the Mertz polynya is primarily a latent heat polynya.