Quantification of algal iron requirements in the Subantarctic Southern Ocean.

• Main Authors: Blain, Stéphane, Sedwick, Peter, Griffiths, Brian, Queguiner, Bernard, Bucciarelli, Eva, Fiala, Michel, Pondaven, Philippe, Tréguer, Paul
• Other Authors: Laboratoire d'océanographie et de biogéochimie (LOB), Université de la Méditerranée - Aix-Marseille 2-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Bermuda Biological Station for Research (BBSR), Bermuda Biological Station for Research, Institute of Antarctic and Southern Ocean Studies (IASOS), University of Tasmania Hobart, Australia (UTAS), Division of Marine and Atmospheric Research (CSIRO), Commonwealth Scientific and Industrial Research Organisation Canberra (CSIRO), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'océanographie biologique de Banyuls (LOBB), Observatoire océanologique de Banyuls (OOB), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2002
• Subjects: algal iron requirements; Subantarctic Southern Ocean (Indian sector); [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Southern Ocean; Indian
• Online Access: https://hal.science/hal-00480620

International audience Shipboard iron-addition incubation experiments were carried out in the Indian sector of the Subantarctic Southern Ocean duringthe Antares-IV campaign in late January–February 1999. The aim of these experiments was to estimate the dissolved iron requirements of the native phytoplankton community in this oceanic region, in order to improve the parameterisation of iron as a limitingnutrient in a coupled 1D physical–biogeochemical ocean model. The experiments were conducted with plankton collected from the upper water column (B20m depth) at three sites in the Crozet Basin between 43–461S and 61–651E: (1) the Polar Front Zone (PFZ, dissolved Fe=0.33 nM), (2) the confluence of the Subantarctic and Subtropical Fronts (SAF/STF, dissolved Fe=0.29 nM), and (3) the southern Subtropical Zone (STZ, dissolved Fe=0.09 nM). Experimental results from each site indicate that algal community growth rates varied as a function of added iron concentration. Monod saturation functions fitted to the experimental data yield estimates for the community half-saturation constant for growth with respect to iron (Km) of 0.41–0.45nM Fe (PFZ), 0.055–0.086nM Fe (SAF/STF) and 0.092–0.093nM Fe (STZ, with macronutrients added), each of which has an estimated uncertainty of 720%. The Km estimate for the SAF/STF site reflects the mixed algal assemblage (diatoms+nanoplankton+dinoflagellates) that grew in the experimental incubations, whereas the Km estimates for the PFZ and STZ sites probably reflect the Fe requirements of the small pennate diatoms such as Pseudo-nitzschia spp., which dominated the algal biomass produced in these experiments. The fact that there are significant differences between the Km estimates for the PFZ and STZ sites suggests that similar diatom assemblages may have quite different iron requirements, perhaps due to differences in environmental conditions (e.g., light, macronutrient levels). We also examine the sensitivity of a onedimensional coupled physical–biogeochemical model to the choice of Km for ...