The University of Southampton
University of Southampton Institutional Repository

The fate of added iron during a mesoscale fertilisation experiment in the polar Southern Ocean

The fate of added iron during a mesoscale fertilisation experiment in the polar Southern Ocean
The fate of added iron during a mesoscale fertilisation experiment in the polar Southern Ocean
The first Southern Ocean Iron RElease Experiment (SOIREE) was performed during February 1999 in Antarctic waters south of Australia (61°S, 140°E), in order to verify whether iron supply controls the magnitude of phytoplankton production in this high nutrient low chlorophyll (HNLC) region. This paper describes iron distributions in the upper ocean during our 13-day site occupation, and presents a pelagic iron budget to account for the observed losses of dissolved and total iron from waters of the fertilised patch. Iron concentrations were measured underway during daily transects through the patch and in vertical profiles of the 65-m mixed layer. High internal consistency was noted between data obtained using contrasting sampling and analytical techniques. A pre-infusion survey confirmed the extremely low ambient dissolved (0.1 nM) and total (0.4 nM) iron concentrations. The initial enrichment elevated the dissolved iron concentration to 2.7 nM. Thereafter, dissolved iron was rapidly depleted inside the patch to 0.2–0.3 nM, necessitating three re-infusions.
A distinct biological response was observed in iron-fertilised waters, relative to outside the patch, unequivocally confirming that iron limits phytoplankton growth rates and biomass at this site in summer. Our budget describing the fate of the added iron demonstrates that horizontal dispersion of fertilised waters (resulting in a quadrupling of the areal extent of the patch) and abiotic particle scavenging accounted for most of the decreases in iron concentrations inside the patch (31–58% and 12–49% of added iron, respectively). The magnitude of these loss processes altered towards the end of SOIREE, and on days 12–13 dissolved (1.1 nM) and total (2.3 nM) iron concentrations remained elevated compared to surrounding waters. At this time, the biogenic iron pool (0.1 nM) accounted for only 1–2% of the total added iron. Large pennate diatoms (>20 m) and autotrophic flagellates (2–20 m) were the dominant algal groups in the patch, taking up the added iron and representing 13% and 39% of the biogenic iron pool, respectively. Iron regeneration by grazers was tightly coupled to uptake by phytoplankton and bacteria, indicating that biological Fe cycling within the bloom was self-sustaining. A concurrent increase in the concentration of iron-binding ligands on days 11–12 probably retained dissolved iron within the mixed layer. Ocean colour satellite images in late March suggest that the bloom was still actively growing 42 days after the onset of SOIREE, and hence by inference that sufficient iron was maintained in the patch for this period to meet algal requirements. This raises fundamental questions regarding the biogeochemical cycling of iron in the Southern Ocean and, in particular, how bioavailable iron was retained in surface waters and/or within the biota to sustain algal growth.
0967-0645
2703-2743
Bowie, A.R.
9e60fe12-98c0-4ea7-9c2f-126a997a9f7b
Maldonado, M.T.
38897f63-a599-483b-852b-846e35bf73f7
Frew, R.D.
e6f76497-4288-4caa-8ddb-52cb3f246e50
Croot, P.L.
25daf592-4186-462b-b0fd-24c70d3fd605
Achterberg, E.P.
685ce961-8c45-4503-9f03-50f6561202b9
Mantoura, R.F.C.
fb0c3cf3-3a51-4557-a732-bd623cf703a0
Worsfold, P.J.
2edcddc5-ce8e-4f9f-8628-216a26921979
Law, C.S.
0c6a142a-f74d-4d0b-be17-b091432c1e0d
Boyd, P.W.
1bac0dba-780e-4c14-93e0-4f707061532d
Bowie, A.R.
9e60fe12-98c0-4ea7-9c2f-126a997a9f7b
Maldonado, M.T.
38897f63-a599-483b-852b-846e35bf73f7
Frew, R.D.
e6f76497-4288-4caa-8ddb-52cb3f246e50
Croot, P.L.
25daf592-4186-462b-b0fd-24c70d3fd605
Achterberg, E.P.
685ce961-8c45-4503-9f03-50f6561202b9
Mantoura, R.F.C.
fb0c3cf3-3a51-4557-a732-bd623cf703a0
Worsfold, P.J.
2edcddc5-ce8e-4f9f-8628-216a26921979
Law, C.S.
0c6a142a-f74d-4d0b-be17-b091432c1e0d
Boyd, P.W.
1bac0dba-780e-4c14-93e0-4f707061532d

Bowie, A.R., Maldonado, M.T., Frew, R.D., Croot, P.L., Achterberg, E.P., Mantoura, R.F.C., Worsfold, P.J., Law, C.S. and Boyd, P.W. (2001) The fate of added iron during a mesoscale fertilisation experiment in the polar Southern Ocean. Deep Sea Research Part II: Topical Studies in Oceanography, 48, 2703-2743. (doi:10.1016/S0967-0645(01)00015-7).

Record type: Article

Abstract

The first Southern Ocean Iron RElease Experiment (SOIREE) was performed during February 1999 in Antarctic waters south of Australia (61°S, 140°E), in order to verify whether iron supply controls the magnitude of phytoplankton production in this high nutrient low chlorophyll (HNLC) region. This paper describes iron distributions in the upper ocean during our 13-day site occupation, and presents a pelagic iron budget to account for the observed losses of dissolved and total iron from waters of the fertilised patch. Iron concentrations were measured underway during daily transects through the patch and in vertical profiles of the 65-m mixed layer. High internal consistency was noted between data obtained using contrasting sampling and analytical techniques. A pre-infusion survey confirmed the extremely low ambient dissolved (0.1 nM) and total (0.4 nM) iron concentrations. The initial enrichment elevated the dissolved iron concentration to 2.7 nM. Thereafter, dissolved iron was rapidly depleted inside the patch to 0.2–0.3 nM, necessitating three re-infusions.
A distinct biological response was observed in iron-fertilised waters, relative to outside the patch, unequivocally confirming that iron limits phytoplankton growth rates and biomass at this site in summer. Our budget describing the fate of the added iron demonstrates that horizontal dispersion of fertilised waters (resulting in a quadrupling of the areal extent of the patch) and abiotic particle scavenging accounted for most of the decreases in iron concentrations inside the patch (31–58% and 12–49% of added iron, respectively). The magnitude of these loss processes altered towards the end of SOIREE, and on days 12–13 dissolved (1.1 nM) and total (2.3 nM) iron concentrations remained elevated compared to surrounding waters. At this time, the biogenic iron pool (0.1 nM) accounted for only 1–2% of the total added iron. Large pennate diatoms (>20 m) and autotrophic flagellates (2–20 m) were the dominant algal groups in the patch, taking up the added iron and representing 13% and 39% of the biogenic iron pool, respectively. Iron regeneration by grazers was tightly coupled to uptake by phytoplankton and bacteria, indicating that biological Fe cycling within the bloom was self-sustaining. A concurrent increase in the concentration of iron-binding ligands on days 11–12 probably retained dissolved iron within the mixed layer. Ocean colour satellite images in late March suggest that the bloom was still actively growing 42 days after the onset of SOIREE, and hence by inference that sufficient iron was maintained in the patch for this period to meet algal requirements. This raises fundamental questions regarding the biogeochemical cycling of iron in the Southern Ocean and, in particular, how bioavailable iron was retained in surface waters and/or within the biota to sustain algal growth.

This record has no associated files available for download.

More information

Published date: 2001

Identifiers

Local EPrints ID: 12560
URI: http://eprints.soton.ac.uk/id/eprint/12560
ISSN: 0967-0645
PURE UUID: 8d599334-4eda-48a3-a7d7-6a3bf85fc64c

Catalogue record

Date deposited: 02 Dec 2004
Last modified: 15 Mar 2024 05:06

Export record

Altmetrics

Contributors

Author: A.R. Bowie
Author: M.T. Maldonado
Author: R.D. Frew
Author: P.L. Croot
Author: E.P. Achterberg
Author: R.F.C. Mantoura
Author: P.J. Worsfold
Author: C.S. Law
Author: P.W. Boyd

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×