High primary production and vertical export of carbon over the Kerguelen Plateau as a consequence of natural iron fertilization in a high-nutrient, low-chlorophyll environment
The KEOPS cruise took place during the austral summer of 2005 on the Kerguelen Plateau. The annual bloom of the plateau is correlated with the iron supply from bottom waters as a result of internal waves generated by the tide. Fertilization allows an intense bloom of diatoms that use the stock of available silicic acid; silicon becomes limiting at the end of the productive period. Surprisingly, the intensity of nitrogen regeneration maintains the use of the nitrate stock at a very low level and diatoms grow using ammonium regenerated by heterotrophs. The phytoplankton assemblages that develop in the core of the bloom are very different from those encountered in the HNLC (high nutrient, low chlorophyll) area. Diatom biodiversity is affected by the fertilization process. The development of the bloom leads to a decrease in concentrations of dissolved inorganic carbon (DIC) and an increased vertical export of carbon. The results of KEOPS highlight the complex behavior of natural systems and the major differences with results obtained by artificial mesoscale fertilization experiments.