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Keywords:

dinoflagellate gymnodinium-sanguineum, belgian coastal waters, equatorial pacific-ocean, long-term incubations, marine-phytoplankton, nitrogen nutrition, biochemical fractionation, c-14 bicarbonate, scotia seas, fatty-acids, 0402 Geochemistry, 0405 Oceanography, 0602 Ecology, Oceanography

Abstract:

The physiological responses of plankton to iron enrichment were investigated in experiments performed in 20-1 culture vessels. Natural phytoplankton communities in sea water, with mean ambient Fe concentrations ranging from 0.3-0.4 nM in the Antarctic Circumpolar Current to 1.2-1.9 nM in the Polar Frontal region, were incubated for several days. Upon addition of 2 nM of iron, synthesis of chlorophyll a and nutrient uptake was stimulated. The specific nitrate-uptake rates as determined by N-15-uptake experiments consistently increased, as well. as the ratios of chlorophyll a to particulate carbon. Growth rates in iron-enriched bottles were consequently enhanced relative to control bottles. The biochemical composition of the plankton community, indicated by carbon to nitrogen ratios and fatty acid composition, remained unaffected by iron addition. On the basis of C-14 incorporation into the major biochemical pools, no changes were observed in the allocation of carbon into proteins, polysaccharides, lipids and low-molecular-weight metabolites in the particulate fraction. Antarctic phytoplankton endures the low ambient iron concentrations by maintaining physiological processes at lower activity rates, whereas the biochemical composition of the plankton remains virtually unaffected. (C) 1997 Elsevier Science Ltd.