Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 12, 4421-4445, 2015
https://doi.org/10.5194/bg-12-4421-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
29 Jul 2015
Iron budgets for three distinct biogeochemical sites around the Kerguelen Archipelago (Southern Ocean) during the natural fertilisation study, KEOPS-2
A. R. Bowie1,2,3, P. van der Merwe1, F. Quéroué1,2,3, T. Trull1,4, M. Fourquez2,5, F. Planchon3, G. Sarthou3, F. Chever3,a, A. T. Townsend6, I. Obernosterer5, J.-B. Sallée7,8,9, and S. Blain5 1Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), Private Bag 80, Hobart, Tasmania 7001, Australia
2Institute for Marine and Antarctic Studies (IMAS), University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia
3Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR6539 UBO/CNRS/IRD/IFREMER, Institut Universitaire Européen de la Mer (IUEM), Technopole Brest Iroise, 29280 Plouzané, France
4CSIRO Marine and Atmospheric Research, Castray Esplanade, Hobart, Tasmania 7000, Australia
5Université Pierre et Marie Curie, Laboratoire d'Océanographie Microbienne (LOMIC), UMR 7621 CNRS UPMC, Avenue du Fontaulé, 66650 Banyuls sur mer, France
6Central Science Laboratory (CSL), University of Tasmania, Private Bag 74, Hobart, Tasmania 7001, Australia
7Sorbonne Universités, UPMC Univ., Paris 06, UMR 7159, LOCEAN-IPSL, 75005 Paris, France
8CNRS, UMR 7159, LOCEAN-IPSL, 75005 Paris, France
9British Antarctic Survey, High Cross, Cambridge CB3 0ET, UK
anow at: National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, UK
Abstract. Iron availability in the Southern Ocean controls phytoplankton growth, community composition and the uptake of atmospheric CO2 by the biological pump. The KEOPS-2 (KErguelen Ocean and Plateau compared Study 2) "process study", took place around the Kerguelen Plateau in the Indian sector of the Southern Ocean. This is a region naturally fertilised with iron on the scale of hundreds to thousands of square kilometres, producing a mosaic of spring blooms which show distinct biological and biogeochemical responses to fertilisation. This paper presents biogeochemical iron budgets (incorporating vertical and lateral supply, internal cycling, and sinks) for three contrasting sites: an upstream high-nutrient low-chlorophyll reference, over the plateau and in the offshore plume east of the Kerguelen Islands. These budgets show that distinct regional environments driven by complex circulation and transport pathways are responsible for differences in the mode and strength of iron supply, with vertical supply dominant on the plateau and lateral supply dominant in the plume. Iron supply from "new" sources (diffusion, upwelling, entrainment, lateral advection, atmospheric dust) to the surface waters of the plume was double that above the plateau and 20 times greater than at the reference site, whilst iron demand (measured by cellular uptake) in the plume was similar to that above the plateau but 40 times greater than at the reference site. "Recycled" iron supply by bacterial regeneration and zooplankton grazing was a relatively minor component at all sites (< 8 % of new supply), in contrast to earlier findings from other biogeochemical iron budgets in the Southern Ocean. Over the plateau, a particulate iron dissolution term of 2.5 % was invoked to balance the budget; this approximately doubled the standing stock of dissolved iron in the mixed layer. The exchange of iron between dissolved, biogenic particulate and lithogenic particulate pools was highly dynamic in time and space, resulting in a decoupling of the iron supply and carbon export and, importantly, controlling the efficiency of fertilisation.

Citation: Bowie, A. R., van der Merwe, P., Quéroué, F., Trull, T., Fourquez, M., Planchon, F., Sarthou, G., Chever, F., Townsend, A. T., Obernosterer, I., Sallée, J.-B., and Blain, S.: Iron budgets for three distinct biogeochemical sites around the Kerguelen Archipelago (Southern Ocean) during the natural fertilisation study, KEOPS-2, Biogeosciences, 12, 4421-4445, https://doi.org/10.5194/bg-12-4421-2015, 2015.
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Iron biogeochemical budgets during the natural ocean fertilisation experiment KEOPS-2 showed that complex circulation and transport pathways were responsible for differences in the mode and strength of iron supply, with vertical supply dominant on the plateau and lateral supply dominant in the plume. The exchange of iron between dissolved, biogenic and lithogenic pools was highly dynamic, resulting in a decoupling of iron supply and carbon export and controlling the efficiency of fertilization.
Iron biogeochemical budgets during the natural ocean fertilisation experiment KEOPS-2 showed...
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