Water Masses and Mixing Near the Antarctic Slope Front

Abstract

The most important water mass for mixing processes at the continental margin of Antarctica is Circumpolar Deep Water (CDW) from the Antarctic Circumpolar Current. The varying characteristics of the CDW near the continental slope of Antarctica are traced around the continent, and the neutral density at the temperature maximum of CDW is proposed to define the top of the CDW layer. The bottom of the CDW layer is considered to be the densest water with a circumpolar distribution. We define the other water masses of the continental margin relative to the regional variety of CDW. Antarctic Surface Water is lighter than CDW, and Antarctic Bottom Water is denser. Shelf Water is denser than CDW and colder than θ=−1.7°C. Various mixtures involving CDW are called Modified CDW if they have the same density as the regional variety of CDW offshore from the slope, but are colder. To identify common features of the continental slope region, nine vertical sections of temperature and salinity and the corresponding θ-S diagrams from different sectors are examined. The most prominent feature of the slope is the Antarctic Slope Front, which we associate with the westward-flowing Antarctic slope current. The structure of the density field at the Front changes, depending on the density of water on the continental shelf. The Antarctic Slope Front appears to be a continuous feature throughout the central and western Pacific, Indian and Atlantic sectors of the Southern Ocean, extending westward from 120° W in the Amundsen Sea to Drake Passage. The Antarctic Slope Front seems to be instrumental in the production of Modified CDW which, in turn, contributes salinity to facilitate the formation of Shelf Water.