Iron and manganese in the wake of the Kerguelen Islands (Southern Ocean)

As part of the ANTARES 3/F-JGOFS cruise, the distributions of dissolved iro n and manganese were measured in October 1995 in the north-east wake of the Kerguelen archipelago (48 degrees 40'-49 degrees 40'S, 68 degrees 70'-70 d egrees 50'E), an area that shows high phytoplankton biomass (CZCS and SeaWi FS data) in the middle of the High Nutrient Low Chlorophyll (HNLC) Southern Ocean. The study area (about 25,000 km(2)) comprised a branch of the Polar Front with Antarctic surface water (AASW) intruding northward, shouldering the shelf break of the Kerguelen Plateau. The coastal zone was clearly aff ected by material of lithogenic origin (riverine discharges, soil leaching by rain waters, aeolian inputs), as well as by inputs from the sediments (e ffluxes from the sediment-water interface, resuspension 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 manga nese concentrations in these waters were 0.46-0.71 and 0.68-1.3 nM, i.e. fa r over typical antarctic open ocean surface water concentrations of 0.16 nM for iron [Martin, J.H., Gordon, R.M., Fitzwater, S.E., 1990. Iron in Antar ctic waters. Nature, 345: 156-158.] and around 0.1 nM for manganese [Martin , J.H., Gordon, R.M., Fitzwater, S.E., 1990. Iron in Antarctic waters. Natu re, 345: 156-158; Sedwick, P.N., Edwards, P.R., Mackey, D.J., Griffiths, F. B., Parslow, J.S., 1997. Iron and manganese in surface waters of the Austra lian subantarctic region. Deep-Sea Res., 44: 1239-1253.]. The dissolved iro n enrichment in coastal waters of the Kerguelen Islands is much more import ant (about 10 times for dissolved iron) than for the Galapagos Islands, ano ther oasis in the HNLC Equatorial oceanic system, where the concentration i ncrease in dissolved iron in the surface waters around the islands is mostl y driven by upwelling of the Equatorial Under Current (EUC) as it reaches t he Galapagos Platform. (C) 2001 Elsevier Science B.V. All rights reserved.