A biogeochemical study of the island mass effect in the context of the Iron Hypothesis : Kerguelen Islands, Southern Ocean.

International audienceAs part of the ANTARES 3/F-JGOFS cruise, the distributions of dissolved iron and manganese were measured in October 1995 in the north-east wake of the Kerguelen archipelago, an area that shows high phytoplankton biomass in the middle of the high nutrient low chlorophyll Southern Ocean. The study area comprised a branch of the Polar Front with Antarctic Surface Water intruding northward shouldering the shelf break of the Kerguelen Plateau. The coastal zone was clearly affected by material of lithogenic origin as well as by inputs from the sediments, its near surface waters showing considerable enrichment in dissolved iron (5.3-12.6 nM) and in dissolved manganese (2.9-8.6 nM). The offshore waters, although less enriched in trace-metals, were also affected by trace-metal inputs from coastal and continental shelf origin. Dissolved iron and manganese concentrations in these waters were 0.46-0.71 nM and 0.68-1.3 nM, i.e. far over typical antarctic open ocean surface water concentrations. The dissolved iron enrichment in coastal waters of the Kerguelen Islands is much more important (about ten times) than for the Galapagos Islands, another oasis in the HNLC Equatorial oceanic system, where the concentration increase in dissolved iron in the surface waters around the islands is mostly driven by upwelling of the Equatorial UnderCurrent as it reaches the Galapagos Platform