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

Published online by Cambridge University Press:  27 October 2009

P. V. Shirodkar ,
J. I. Goes ,
R. Alagarsamy  and
S. P. Fondekar
P. V. Shirodkar
Affiliation:
National Institute of Oceanography, Dona Paula, Goa 403 004, India.
J. I. Goes
Affiliation:
National Institute of Oceanography, Dona Paula, Goa 403 004, India.
R. Alagarsamy
Affiliation:
National Institute of Oceanography, Dona Paula, Goa 403 004, India.
S. P. Fondekar
Affiliation:
National Institute of Oceanography, Dona Paula, Goa 403 004, India.
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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 (PO4-P) was significantly correlated with nitrate-nitrogen (NO3-N) and inversely correlated with primary productivity and chlorophyll a, indicating the utilization of PO4-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.

Type
Articles
Information
Polar Record , Volume 28 , Issue 165 , April 1992 , pp. 127 - 136
Copyright
Copyright © Cambridge University Press 1992

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