Distributions and sources of dissolved iron in the polar oceans

PhD ceremony: Mr. M.B. Klunder, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Distributions and sources of dissolved iron in the polar oceans

Promotor(s): prof. H.J.W. de Baar

Faculty: Mathematics and Natural Sciences

The availability of iron is very important for algal growth in the ocean, thus for the entire ocean food web. Maarten Klunder investigated the distribution and sources of dissolved iron in the Polar Oceans. Iron is measured in high resolution in water samples divided over the entire depth of the ocean. In the Arctic Ocean it appeared that iron from the Siberian rivers is transported with the Transpolar Drift and reaches the middle of the Arctic Ocean. Further towards the Canadian side, iron concentrations decrease the concentration is determined by melting ice and biological factors. In the deep Arctic Ocean, hydrothermal vents are an important source of iron. In the Makarov Basin, a low iron concentration is attributed to the lack of input sources and the influence of organic ligands. In the Southern Ocean an inverse relation between fluorescence, indicative for algal growth, and dissolved iron is found. The common pattern of increasing iron concentrations towards continental shelves is not present in the Weddell Sea, likely as a result of the ice sheet extending far beyond the continent. Local sources of iron are dust deposition at the surface and hydrothermal vents at depth. At the zero meridian the nitrate:phosphate and nitrate:silicate uptake increases with dissolved iron whereas in the Western Weddell Sea there was no relation. This can be explained by the significantly larger algae at the zero meridian, for which there is a much larger effect of iron on the nutrient uptake and thus on the growth.