Benthic supply of iron to the ocean

Iron is essential to the growth of marine micro-organisms, and when concentrations are low (such as in high nutrient low chlorophyll [HNLC] areas) the amount of carbon dioxide taken up through the biological pump is reduced, and the types of organism present are very different to those when Fe is plentiful. However, many aspects of Fe biogeochemistry are poorly known and in particular the role of sedimentary sources that may be a major supply term of Fe are not understood. Satellite images of the Southern Ocean in the austral Spring show high chlorophyll levels downstream of islands in this otherwise biologically barren region. Here we will test the hypothesis that sediments around Crozet island provide a benthic source of iron to the surface ocean and biota, thus leading to the high chlorophyll, and investigate the forms and organic associations of the Fe released from the island system as a model for benthic Fe sources. As background Fe is low and other sources weak, this is an excellent natural laboratory to study benthic Fe sources. The work will use 1) electrochemical and chemiluminescent methods coupled to size fractionation techniques to elucidate concentrations and the forms of iron and iron ligands, and 2) novel radium tracing techniques for waters that have recently been in contact with sediments will provide a time-frame for the dispersion of water and fate of iron in the water.