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A tale of three islands: downstream natural iron fertilization in the Southern Ocean

A tale of three islands: downstream natural iron fertilization in the Southern Ocean
A tale of three islands: downstream natural iron fertilization in the Southern Ocean
Iron limitation of primary productivity prevails across much of the Southern Ocean but there are exceptions; in particular, the phytoplankton blooms associated with the Kerguelen Plateau, Crozet Islands and South Georgia. These blooms occur annually, fertilized by iron and nutrient-rich shelf waters that are transported downstream from the islands. Here we use a highresolution (1/12°) ocean general circulation model and Lagrangian particle tracking to investigate whether inter-annual variability in the potential lateral advection of iron, could explain the inter-annual variability in the spatial extent of the blooms. Comparison with ocean color data, 1998 to 2007, suggests that iron fertilization via advection can explain the extent of each island's annual bloom, but only the inter-annual variability of the Crozet bloom. The area that could potentially be fertilized by iron from Kerguelen was much larger than the bloom, suggesting that there is another primary limiting factor, potentially silicate, that controls the inter-annual variability of bloom spatial extent. For South Georgia, there are differences in the year-to-year timing of advection and consequently fertilization, but no clear explanation of the inter-annual variability observed in the bloom's spatial extent has been identified. The model results suggest that the Kerguelen and Crozet blooms are terminated by nutrient exhaustion, probably iron and or silicate, whereas the deepening of the mixed layer in winter terminates the South Georgia bloom. Therefore, iron fertilization via lateral advection alone can explain the annual variability of the Crozet bloom, but not fully that of the Kerguelen and South Georgia blooms.
Natural iron fertilization, Advection, Kerguelen, Crozet, South Georgia
3350-3371
Robinson, J.
8812551a-26bb-49c3-801f-67bfb878c7c7
Popova, E.E.
3ea572bd-f37d-4777-894b-b0d86f735820
Srokosz, M.
1e0442ce-679f-43f2-8fe4-9a0f0174d483
Yool, A.
882aeb0d-dda0-405e-844c-65b68cce5017
Robinson, J.
8812551a-26bb-49c3-801f-67bfb878c7c7
Popova, E.E.
3ea572bd-f37d-4777-894b-b0d86f735820
Srokosz, M.
1e0442ce-679f-43f2-8fe4-9a0f0174d483
Yool, A.
882aeb0d-dda0-405e-844c-65b68cce5017

Robinson, J., Popova, E.E., Srokosz, M. and Yool, A. (2016) A tale of three islands: downstream natural iron fertilization in the Southern Ocean. Journal of Geophysical Research: Oceans, 121 (5), 3350-3371. (doi:10.1002/2015JC011319).

Record type: Article

Abstract

Iron limitation of primary productivity prevails across much of the Southern Ocean but there are exceptions; in particular, the phytoplankton blooms associated with the Kerguelen Plateau, Crozet Islands and South Georgia. These blooms occur annually, fertilized by iron and nutrient-rich shelf waters that are transported downstream from the islands. Here we use a highresolution (1/12°) ocean general circulation model and Lagrangian particle tracking to investigate whether inter-annual variability in the potential lateral advection of iron, could explain the inter-annual variability in the spatial extent of the blooms. Comparison with ocean color data, 1998 to 2007, suggests that iron fertilization via advection can explain the extent of each island's annual bloom, but only the inter-annual variability of the Crozet bloom. The area that could potentially be fertilized by iron from Kerguelen was much larger than the bloom, suggesting that there is another primary limiting factor, potentially silicate, that controls the inter-annual variability of bloom spatial extent. For South Georgia, there are differences in the year-to-year timing of advection and consequently fertilization, but no clear explanation of the inter-annual variability observed in the bloom's spatial extent has been identified. The model results suggest that the Kerguelen and Crozet blooms are terminated by nutrient exhaustion, probably iron and or silicate, whereas the deepening of the mixed layer in winter terminates the South Georgia bloom. Therefore, iron fertilization via lateral advection alone can explain the annual variability of the Crozet bloom, but not fully that of the Kerguelen and South Georgia blooms.

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More information

Accepted/In Press date: 13 April 2016
e-pub ahead of print date: 22 May 2016
Published date: May 2016
Keywords: Natural iron fertilization, Advection, Kerguelen, Crozet, South Georgia
Organisations: Marine Systems Modelling, Physical Oceanography, Marine Physics and Ocean Climate

Identifiers

Local EPrints ID: 393481
URI: http://eprints.soton.ac.uk/id/eprint/393481
PURE UUID: ea7fa469-4097-4b64-9359-5121e0f517c1

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Date deposited: 26 Apr 2016 13:57
Last modified: 15 Mar 2024 00:02

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Contributors

Author: J. Robinson
Author: E.E. Popova
Author: M. Srokosz
Author: A. Yool

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