Major elements, nutrients, and plankton biomass in the ice edge and an offshore region of the Indian Ocean sector of the Southern Ocean

• Published in: Polar Record
• Main Authors: Shirodkar, P. V., Goes, J. I., Alagarsamy, R., Fondekar, S. P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1992
• Subjects: General Earth and Planetary Sciences; Ecology; Geography, Planning and Development; Antarctic; Southern Ocean; Austral; Indian; Antarc*; Antarctica; Polar Record
• Online Access: http://dx.doi.org/10.1017/s0032247400013425; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0032247400013425

Abstract Physico-chemical and biological studies during the austral summer of 1986–87 in the ice-edge and a region offshore of Antarctica indicated significant spatial differences in concentrations of nutrients, dissolved oxygen (DO), Ca, Mg, and chlorophyll a , and in the rates of primary production. The waters within the ice-edge region were richer in nutrients and DO and showed a four-fold increase in chlorophyll a (1.98 mg m -3 ) and a 10-fold increase in primary productivity (0.74 mg C m -3 h -1 ) as compared with offshore waters. In the ice-edge region, Mg was high (1319 mg kg -1 ), whereas values of Ca (421.7 mg kg -1 ) were within the normal range. Offshore Ca (423.8 mg kg -1 ) and Mg (1297 mg kg -1 ) were within the expected limits. In the ice-edge region, Ca/Cl varied from 0.0202 to 0.0229, with a mean of 0.0220, and Mg/Cl varied from 0.0637 to 0.0737, with a mean of 0.0687. These figures were slightly higher than those offshore (Ca/Cl: 0.0205 to 0.0224, mean 0.0214; Mg/Cl: 0.0630 to 0.0693, mean 0.0657), indicating the addition of Mg to the waters in the ice-edge region. Nutrients in the ice-edge region showed increasing concentrations at deeper levels irrespective of their relationship with DO, indicating large amounts of preformed nutrients, a characteristic of Antarctic waters attributable to intense upwelling. Chlorophyll a showed a direct relation with primary productivity and an inverse relation with Mg, suggesting the release of Mg from biogenic matter. Offshore, phosphate-phosphorus (PO 4 -P) was significantly correlated with nitrate-nitrogen (NO 3 -N) and inversely correlated with primary productivity and chlorophyll a , indicating the utilization of PO 4 -P during high production. Significantly elevated concentrations of chlorophyll a, primary productivity and Mg, marked by a considerable decrease in nutrients, were observed at a frontal zone between 64° and 62°S.