Iron budgets for three distinct biogeochemical sites around the Kerguelen Archipelago (Southern Ocean) during the natural fertilisation study, KEOPS-2

Type Article
Date 2015
Language English
Author(s) Bowie A. R.1, 2, 3, Van Der Merwe P.1, Queroue Fabien1, 2, 3, Trull Thomas1, 4, Fourquez M.2, 5, Planchon F.3, Sarthou Geraldine3, Chever Fanny3, Townsend A. T.6, Obernosterer I.5, Sallee Jean-Baptiste7, 8, 9, Blain S.5
Affiliation(s) 1 : ACE CRC, Hobart, Tas 7001, Australia.
2 : Univ Tasmania, IMAS, Hobart, Tas 7001, Australia.
3 : IUEM, UBO CNRS IRD IFREMER UMR6539, Lab Sci Environm Marin LEMAR, F-29280 Plouzane, France.
4 : CSIRO Marine & Atmospher Res, Hobart, Tas 7000, Australia.
5 : Univ Paris 06, Lab Oceanog Microbienne LOMIC, UMR CNRS UPMC 7621, F-66650 Banyuls Sur Mer, France.
6 : Univ Tasmania, CSL, Hobart, Tas 7001, Australia.
7 : Univ Paris 06, Sorbonne Univ, UMR 7159, LOCEAN IPSL, F-75005 Paris, France.
8 : CNRS, UMR 7159, LOCEAN IPSL, F-75005 Paris, France.
9 : British Antarctic Survey, Cambridge CB3 0ET, England.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2015 , Vol. 12 , N. 14 , P. 4421-4445
DOI 10.5194/bg-12-4421-2015
WOS© Times Cited 43
Note KEOPS2: Kerguelen Ocean and Plateau Study 2 Editor(s): S. Blain, I. Obernosterer, B. Queguiner, T. Trull, and G. Herndl
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 path-ways 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 bio-geochemical 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 ex-change 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.
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Bowie A. R., Van Der Merwe P., Queroue Fabien, Trull Thomas, Fourquez M., Planchon F., Sarthou Geraldine, Chever Fanny, Townsend A. T., Obernosterer I., Sallee Jean-Baptiste, Blain S. (2015). Iron budgets for three distinct biogeochemical sites around the Kerguelen Archipelago (Southern Ocean) during the natural fertilisation study, KEOPS-2. Biogeosciences, 12(14), 4421-4445. Publisher's official version : https://doi.org/10.5194/bg-12-4421-2015 , Open Access version : https://archimer.ifremer.fr/doc/00276/38726/