Journal
DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY
Volume 55, Issue 5-7, Pages 693-705Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.dsr2.2007.12.008
Keywords
iron; phytoplankton; Kerguelen; diatoms; microbial foodweb; Southern Ocean
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Natural phytoplankton assemblages collected in surface waters above the Kerguelen Plateau or in the open-ocean and single-species cultures of Southern Ocean diatoms were used to address the existence and effects of natural iron fertilization near the Kerguelen Islands (Southern Ocean). The phytoplankton was transferred during so-called translocation experiments into water collected at the surface over the Plateau, open-ocean surface water or water collected close to the sediment of the Plateau. These watertypes differed in iron (iron-rich deep water and iron-poor surface water) and silicic acid concentration (silicic acid-rich Plateau deep and open-ocean surface water, silicic acid-poor Plateau surface water). As a general trend in the natural phytoplankton assemblages, cell numbers, chlorophyll autofluorescence, photosynthetic efficiency of photosystem II, chlorophyll a and phytoplankton carbon concentrations increased especially after translocation into Plateau deep water. This response was most pronounced in terms of increase in carbon assimilation in the larger-sized phytoplankton (> 8 mu m in cell diameter), mainly diatoms. Effects of translocation on bacteria and viruses followed those of the phytoplankton. Experiments with single-species cultures of large diatoms (Fragilariopsis kerguelensis, Thalassiosira sp., Chaetoceros dichaeta), which have high it-on requirements, confirmed the observations made for the natural phytoplankton assemblages. Assuming a continuous flux of deep water to the surface over the Kerguelen Plateau, the translocation experiments provide evidence that this water contains the growth-stimulating factor, most likely iron, responsible for the formation of a phytoplankton bloom as is observed over the Kerguelen Plateau. (C) 2008 Elsevier Ltd. All rights reserved.
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