Primary productivity, phytoplankton standing crop and physico-chemical characteristics of the Antarctic and adjacent central Indian Ocean waters

Abstract

Primary productivity, phytoplankton pigments and physico-chemical properties were studied in Antarctic waters and adjoining Indian Ocean between 11 degrees and 67 degrees E longitudes from polynya region (60 degrees S) to equator during the austral summer season viz. 4th January to 23rd March, 1990. The higher concentration of dissolved oxygen (11.33 mg L sup(-1)) due to photosynthesis was observed. The temperature was low (-2.0 degrees to 2.1 degrees C) in the coastal ice-edge zone. Often, temperature recorded above zero, lowered the salinity from 34.9 to 33.16 x 10 sup(-3). Though there was no direct correlation of nutrients to primary productivity, the constant higher concentration of phosphate (av. 4.12 mu mol dm sup(-3)), nitrate (18.67 mu mol dm sup(-3)) and nitrite (2.74 mu mol dm sup(-3)) in the coastal ice zone than those of Antarctic oceanic region (phosphate 3.03, nitrate 16.17 mu mol dm sup(-3)) and central Indian Ocean (phosphate 2.39, nitrate 15.77 and nitrite 2.47 mu mol dm sup(-3)) indicated regeneration of nutrients in the coastal ice-edge zone which supported fairly high growth of phytoplankton (av. 69.89 x 10 sup(4) cells L sup(-1)). This resulted in markedly high values of chlorophyll and primary productivity (av. Chl a) 2.68 mg m sup(-3), PP 1.68 mg C m sup(-3) h sup(-1)) in the coastal ice-edge zone as compared to those in the Antarctic oceanic region (chl. a) 0.74 mg m sup(-3), PP 0.18 mg C m sup(-3) h sup(-1)) and central Indian Ocean (chl a) 1.86 mg m sup(-3), PP 0.55 mg C m sup(-3) h sup(-1)). Fairly higher values of standing crop and column production in the coastal ice-edge zone (av. 179.39 mg m sup(-3) and 15.8 mg m sup(-2) h sup(-1)) than that of Antarctic oceanic region (49.25 mg m sup(-3) and 1.92 mg C m sup(-2) h sup(-1)) and other oceanic region (124.88 mg m sup(-3) and 6.71 mg C m sup(-2) h sup(-1)) suggested the coastal ice edge zone to be far more productive. Low values (0.003-0.009 mg C [mg chl a)] sup(-1) h sup(-1)) of assimilation number (AN) or photosynthetic rate and high concentration of phaeophytin (av. 12.35-23.50 mg m sup(-3)) recorded in floating ice samples was the indication of unhealthy phytoplankton cells frozen in the ice