The South Pacific Subtropical Mode Water in the Tasman Sea

Abstract

From the synopical CTD sections in the WOCE PR11 repeated cruises, the South Pacific Subtropical Mode Water (SPSTMW) has been identified in the region of the Tasman Front Extension (TFE) around 29’S to the east of Australia. In the depth range of 150–250m, the SPSTMW appears as a thermostad with vertical temperature gradient lower than 1.6°C (100 m)−1 and a temperature range of 16.5–19.5°C and as a pycnostad with PV lower than 2 × 10−10m−1s−1 and a potential density range of 25.4–26.0 kg m−3. Like the subtropical mode waters in the North Atlantic and North Pacific, the formation of the SPSTMW is associated with the convective mixing during the austral wintertime as manifested from the time series of the Argo floats. And cold water entrains into the mixed layer with the deepening mixed layer from September to the middle of October. During the wintertime formation process, mesoscale eddies prevailing in the TFE region play an important role in the SPSTMW formation, and have a great effect on the SPSTMW distribution in the next year. The deeper (shallower) mixed layer in wintertime, consistent with the depressed (uplifted) permanent thermocline, is formed by the anticyclonic (cyclonic) eddies, and the substantial mode water thicker than 50 m is mainly found in the region of the anticyclonic eddies where the permanent thermocline is deeper than 450 m.