WHOI PO

Seasonal changes in water mass properties are discussed in thermohaline coordinates. Examples are presented from Drake Passage using the SR1b CTD transects and the CSIRO atlas of regional seas seasonal climatology. In addition, the analysis will be presented for the whole Southern Ocean using the recent release of the ECCO state estimate. The amount of water within temperature and salinity classes and changes therein are used to estimate transports across iso-therms and iso-halines. These transports are considered in combination with surface buoyancy flux climatologies to determine the relative contributions of surface buoyancy fluxes and sub-surface mixing to changes in the distribution of water in thermohaline coordinates. The framework developed provides unique insights into the water masses that are present within Drake Passage, including the erosion of Antarctic Winter Water (AAWW) during the summer months and the interaction between the Circumpolar Deep Waters (CDW) and Antarctic Intermediate Water (AAIW). The results presented are consistent with summertime wind-driven inflation of the CDW layer and deflation of the AAIW layer, with the production of new AAIW occurring in the winter as a mixture of CDW, remnant AAWW and surface waters.