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Fluxes of particulate iron from the upper ocean around the Crozet Islands: A naturally iron-fertilized environment in the Southern Ocean

Fluxes of particulate iron from the upper ocean around the Crozet Islands: A naturally iron-fertilized environment in the Southern Ocean
Fluxes of particulate iron from the upper ocean around the Crozet Islands: A naturally iron-fertilized environment in the Southern Ocean
Despite a large macronutrient reservoir, the Southern Ocean has low levels of chlorophyll, primarily due to low iron availability. Exceptions to this situation are island systems where natural terrestrial iron inputs allow the development of large blooms. Particulate organic carbon (POC) and particulate (labile and refractory) iron analyses were performed on large (>53 ?m) particles collected at the base of the mixed layer within such a system (the Crozet Islands) and in adjacent high-nutrient, low-chlorophyll (HNLC) waters. Biogenic iron was obtained by removal of estimated lithogenic Fe from the total Fe present. We combine these data with 234Th measurements to determine downward particulate Fe fluxes. Fluxes of Fe ranged from 4 to 301 nmol m?2 d?1 (labile), not detectable to 50 ?mol m?2 d?1 (biogenic), and from 3 to 145 ?mol m?2 d?1 (total) and, on average, were approximately four times larger below the highly productive, naturally iron-fertilized region than below the adjacent HNLC area. Downward labile iron fluxes are close to the sum of dissolved terrestrial, atmospheric, and upwelled iron calculated from the Planquette et al. (2007), model. Refractory iron fluxes are ?2 orders of magnitude larger, and these can only have come from particles advected from the plateau itself. The “biogenic Fe,” is a substantial fraction (0–76, mean 23%) of the total particulate Fe to the north of the islands. The origin of this Fe pool must be dominantly biological conversion from the lithogenic fraction, as other supply terms including aeolian, deep mixing, and lateral advection of dissolved Fe are inadequate to account for the magnitude of this Fe. Inclusion of the offshore biologically available fraction of the lithogenic iron flux is therefore required to calculate fully the yield of carbon exported per unit iron injected.
0886-6236
GB2011
Planquette, Hélène
99d8fde6-e561-47f0-9854-a35d42edfd26
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Statham, Peter J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Morris, Paul J.
05f4f629-e810-4679-a2c5-73611ce9660f
Fones, Gary R.
304f9c63-0e4d-4b0b-9240-8a9e8dd2bf85
Planquette, Hélène
99d8fde6-e561-47f0-9854-a35d42edfd26
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Statham, Peter J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Morris, Paul J.
05f4f629-e810-4679-a2c5-73611ce9660f
Fones, Gary R.
304f9c63-0e4d-4b0b-9240-8a9e8dd2bf85

Planquette, Hélène, Sanders, Richard, Statham, Peter J., Morris, Paul J. and Fones, Gary R. (2011) Fluxes of particulate iron from the upper ocean around the Crozet Islands: A naturally iron-fertilized environment in the Southern Ocean. Global Biogeochemical Cycles, 25 (2), GB2011. (doi:10.1029/2010GB003789).

Record type: Article

Abstract

Despite a large macronutrient reservoir, the Southern Ocean has low levels of chlorophyll, primarily due to low iron availability. Exceptions to this situation are island systems where natural terrestrial iron inputs allow the development of large blooms. Particulate organic carbon (POC) and particulate (labile and refractory) iron analyses were performed on large (>53 ?m) particles collected at the base of the mixed layer within such a system (the Crozet Islands) and in adjacent high-nutrient, low-chlorophyll (HNLC) waters. Biogenic iron was obtained by removal of estimated lithogenic Fe from the total Fe present. We combine these data with 234Th measurements to determine downward particulate Fe fluxes. Fluxes of Fe ranged from 4 to 301 nmol m?2 d?1 (labile), not detectable to 50 ?mol m?2 d?1 (biogenic), and from 3 to 145 ?mol m?2 d?1 (total) and, on average, were approximately four times larger below the highly productive, naturally iron-fertilized region than below the adjacent HNLC area. Downward labile iron fluxes are close to the sum of dissolved terrestrial, atmospheric, and upwelled iron calculated from the Planquette et al. (2007), model. Refractory iron fluxes are ?2 orders of magnitude larger, and these can only have come from particles advected from the plateau itself. The “biogenic Fe,” is a substantial fraction (0–76, mean 23%) of the total particulate Fe to the north of the islands. The origin of this Fe pool must be dominantly biological conversion from the lithogenic fraction, as other supply terms including aeolian, deep mixing, and lateral advection of dissolved Fe are inadequate to account for the magnitude of this Fe. Inclusion of the offshore biologically available fraction of the lithogenic iron flux is therefore required to calculate fully the yield of carbon exported per unit iron injected.

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More information

Published date: 2011
Organisations: Ocean and Earth Science, Marine Biogeochemistry, National Oceanography Centre,Southampton

Identifiers

Local EPrints ID: 191509
URI: http://eprints.soton.ac.uk/id/eprint/191509
ISSN: 0886-6236
PURE UUID: da6d582a-2420-4697-b0cb-a09d103be673

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Date deposited: 21 Jun 2011 15:22
Last modified: 14 Mar 2024 03:45

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Contributors

Author: Hélène Planquette
Author: Richard Sanders
Author: Paul J. Morris
Author: Gary R. Fones

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