Antarctic Surface Water
Antarctic Surface Water (AASW) is a water mass in the Antarctic Zone of the Southern Ocean. AASW is found in the upper 200 meters south of the Polar Front (PF) and is cold, fresh, and high in oxygen and nutrients relative to the subantarctic surface waters, although it is high in nutrients compared to underyling waters.
The most easily distinguishable characteristics of AASW in summer sections is a intense temperature minimum at about 200 m that marks the base of the winter mixed layer. The water around this minimum is also commonly known as Winter Water, and ranges from 50 m deep in the Weddell Gyre to nearly 1000 m immediately north of the PF. It is characterized by extremely low temperatures ranging down to the freezing point of -1.9o C and low salinities as the result of ice melting in the summer in the upper 100-250 m of the water column.
The predominant flow of Antarctic Surface Water is an eastwardly flowing wind driven current known as the Antarctic Circumpolar Current. Features such as the Weddell Gyre in the Weddell Sea act as an overlay to that eastern flowing circumpolar current.
Water Chemistry and Ecology
Nutrient and biomass content is not uniform throughout the Antartic Zone; for example nutrient levels in the Bellingshausen Sea and Amundsen Sea are notably lower than for other parts of the circumpolar seas.
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