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

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posted on 2023-05-18, 13:46 authored by Andrew BowieAndrew Bowie, Pier van der MerwePier van der Merwe, Queroue, F, Trull, T, Fourquez, M, Planchon, F, Sarthou, G, Chever, F, Ashley TownsendAshley Townsend, Obernosterer, I, Sallee, J-B, Blain, S
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.

History

Publication title

Biogeosciences

Volume

12

Issue

14

Pagination

4421-4445

ISSN

1726-4170

Department/School

Institute for Marine and Antarctic Studies

Publisher

Copernicus GmbH

Place of publication

Germany

Rights statement

Copyright 2015 The Authors Licenced under Creative Commons Attribution 3.0 License http://creativecommons.org/licenses/by/3.0/

Repository Status

  • Open

Socio-economic Objectives

Measurement and assessment of marine water quality and condition

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