Biological response to physical processes in the Indian Ocean sector of the Southern Ocean: a case study in the coastal and oceanic waters

The spatial variation of chlorophyll a (Chl a) and factors influencing the high Chl a were studied during austral summer based on the physical and biogeochemical parameters collected near the coastal waters of Antarctica in 2010 and a zonal section along 60°S in 2011. In the coastal waters, high Chl a (>3 mg m⁻³) was observed near the upper layers (∼15 m) between 53°30′E and 54°30′E. A comparatively higher mesozooplankton biomass (53.33 ml 100 m⁻³) was also observed concordant with the elevated Chl a. Low saline water formed by melting of glacial ice and snow, as well as deep mixed-layer depth (60 m) due to strong wind (>11 ms⁻¹) could be the dominant factors for this biological response. In the open ocean, moderately high surface Chl a was observed (>0.6 mg m⁻³) between 47°E and 50°E along with a Deep Chlorophyll Maximum of ∼1 mg m⁻³ present at 30–40 m depth. Melt water advected from the Antarctic continent could be the prime reason for this high Chl a. The mesozooplankton biomass (22.76 ml 100 m⁻³) observed in the open ocean was comparatively lower than that in the coastal waters. Physical factors such as melting, advection of melt water from Antarctic continent, water masses and wind-induced vertical mixing may be the possible reasons that led to the increase in phytoplankton biomass (Chl a).