Chlorophyllα distribution in the Indian sector of the Antarctic Ocean in 1978-1979

Abstract

Horizontal and vertical distributions of chlorophyll a in the Indian sector of the Antarctic Ocean were investigated during the 20th Japanese Antarctic Research Expedition in 1978-1979. Surface observations including the two hours interval observation were carried out on the southward leg between 34°S, 110°E and 60°S, 90°E in middle December, on the westward leg between 90°and 39°E south of 60°S in late December to early January, and on the northward leg between 65°S, 40°E and 34°S, 51°E in late February to early March. Vertical observations down to a 500m depth were done at six stations on the northward leg south of 52°S latitude. While high surface chlorophyll a concentrations (more than 1.0mg/m^3) were seen around the Antarctic Convergence on the southward leg, high concentrations more than 0.5mg/m^3 were distributed around the Subtropical Convergence on the northward leg. Difference in the latitudinal variations of surface chlorophyll a between the two legs suggested the seasonal periodicity of phytoplankton. Longitudinal variation on the westward leg seemed to be related with the upwellings of water. Integrated chlorophyll a stocks for a 0-250m water column were in a range of 16.8-39.4mg/m^2 and a weak subsurface chlorophyll a maximum was seen around 50-100m depths.