Iron in Antarctic waters

Abstract

WE are testing the hypothesis that Antarctic phytoplankton suffer from iron deficiency1–3 which prevents them from blooming and using up the luxuriant supplies of major nutrients found in vast areas of the southern ocean. Here we report that highly productive4 (∼3 g C m−;2 day−1), neritic Gerlache Strait waters have an abundance of Fe (7.4 nmol kg−1) which facilitates phytoplankton blooming and major nutrient removal, while in low-productivity4 (∼0.1 g C m−2 day−1), offshore Drake Passage waters, the dissolved Fe levels are so low (0.16 nmol kg−1) that the phytoplankton are able to use less than 10% of the major nutrients available to them. The verification of present-day Fe deficiency is of interest as iron-stimulated phytoplankton growth may have contributed to the drawing down of atmospheric CO2 during glacial maxima2,3; it is also important because oceanic iron fertilization aimed at the enhancement of phytoplankton production may turn out to be the most feasible method of stimulating the active removal of greenhouse gas CO2 from the atmosphere, if the need arises (J.H.M., manuscript in preparation).