Oceanic fronts along 45 degrees across Antarctic circumpolar current during austral Summer 2004

Abstract

A pilot expedition was launched to monitor the oceanic fronts in the southwestern sector of the Indian Ocean during January–February 2004. Major fronts along 45 degrees E between 40 and 56 degrees S were delineated and their spatial variations during 6–17 February have been compared with earlier studies. The Agulhas Return Front (ARF) has been identified between 40 degrees 15 minutes and 41 degrees 15 minutes S with a change in temperature from 19 to 17 degrees C and a change in salinity from 35.54 to 35.39 ppt at the surface. The position of Subtropical Front (STF) was observed between 41 degrees 15 minutes and 42 degrees 15 minutes S, with a rapid decrease in surface temperature from 17 to 10.6 degrees C and salinity from 35.35 to 34.05 ppt. The Subantarctic Front has been located between latitudes 42 degrees 30 minutes and 47 degrees S, with a change in surface temperature from 9.7 to 6.3 degrees C and change in surface salinity from 34.0 to 33.85 ppt. One of the significant findings here compared to previous studies is the identification of ARF and STF with almost equal width of approx. 110 km. In addition, the Surface Polar Front and the Subsurface Polar Front were also identified between 48 and 52 degrees S. Temperature minimum layer has been located between 49 and 56 degrees S and extends from 150 to 200 m. Its existence has been attributed to the residue of the previous winter mixed layer capped by seasonal warming and freshen-ing. The freshwater input thickness from 49 to 56 degrees S was estimated to be 55 (+) or (-) 15cm, with a major thickness (69 cm) at 54 degrees S. It is suggested that the freshening south of the polar front could be due to the advection of melt water originating from the Weddell Basin.