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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.

Item Type:	Refereed Article
Keywords:	Fe, dissolved iron, Southern Ocean, Kerguelen Island, iron budget
Research Division:	Earth Sciences
Research Group:	Oceanography
Research Field:	Chemical oceanography
Objective Division:	Environmental Management
Objective Group:	Marine systems and management
Objective Field:	Measurement and assessment of marine water quality and condition
UTAS Author:	Bowie, AR (Professor Andrew Bowie)
UTAS Author:	van der Merwe, P (Dr Pier van der Merwe)
UTAS Author:	Queroue, F (Mr Fabien Queroue)
UTAS Author:	Trull, T (Professor Thomas Trull)
UTAS Author:	Fourquez, M (Dr Marion Fourquez)
UTAS Author:	Townsend, AT (Associate Professor Ashley Townsend)
ID Code:	103859
Year Published:	2015
Deposited By:	CRC-Antarctic Climate & Ecosystems
Deposited On:	2015-10-28
Last Modified:	2017-10-31
Downloads:	371 View Download Statistics