Spatiotemporal variability of chlorophyll a in the Atlantic and Indian sectors of the Southern Ocean during February-April of 2000 according to satellite and expeditionary data.

Abstract

In February and April 2000, in the Southern Ocean between Africa and Antarctica, concentration of chlorophyll (Cchs) in the surface layer was not high (0.1-0.3 mg/m**3). Zones of increased Cchs values (0.6-2.0 and over 2.0 mg/m**3) were located between the Southern Subtropical and Subantarctic fronts, near the Polar front, and to the south of the Antarctic Divergence. From February to April, in open areas of the Southern Ocean, a general Cchs decrease was observed. A similar trend was also noted in near-shore seas of the East Antarctic. At the shelf of the Sea of Cosmonauts, within the upper mixed layer, the content of chlorophyll amounted to 0.34-0.37 mg/m**3 . In the area of the continental slope, we registered formation of a subsurface chlorophyll maximum (0.52-0.56 mg/m**3) at 20 m depth, which deepened to 70 m when passing to the deepwater area. The positive correlation with a high coefficient (r = 0.939) between the field and satellite data (Cchs and Csat, respectively) allows one to conclude about applicability of the SeaWiFS algorithm for estimation of chlorophyll content within the surface layer in the Antarctic areas studied. In the course of ice formation in Prydz Bay, during five days, content of chlorophyll in different phases of new ice increased by a factor of 2.9, whereas values of this parameter in the surrounding waters remained quite invariable. The Csat values were 6.3 times as high as those obtained experimentally for sludge ice. Because of large areas occupied by floating ice, the sole usage of satellite data may cause great errors in productivity estimation of for the East Antarctic seas.