The University of Southampton
University of Southampton Institutional Repository

Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX

Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX
Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX
A closed eddy core in the Subantarctic Atlantic Ocean was fertilized twice with two tons of iron (as FeSO 4), and the 300 km2 fertilized patch was studied for 39 days to test whether fertilization enhances downward particle flux into the deep ocean. Chlorophyll a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to ? 0.40. Silicic acid (<2 ?mol L1) limited diatoms, which contributed <10% of phytoplankton biomass. Copepods exerted high grazing pressure. This is the first study of particle flux out of an artificially fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch, estimated from O2:Ar ratios, averaged 21 mmol POC m2 d1, probably±20%. 234Th profiles implied constant export of ~6.3 mmol POC m2 d1 in the patch, similar to unfertilized waters. The difference between NCP and 234Th-derived export partly accumulated in the mixed layer and was partly remineralized between the mixed layer and 100 m. Neutrally buoyant sediment traps at 200 and 450 m inside and outside the patch caught mostly <1.1 mmol POC m2 d1, predominantly of fecal origin; flux did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.
0886-6236
871-881
Martin, Patrick
01ce1c59-3926-46c9-a556-fac39e0ee16b
van der Loeff, Michiel Rutgers
5cbd760d-b52b-46b7-8058-945ea9edfc62
Cassar, Nicolas
77fc58ca-3e20-44b5-b397-801ec4d8f5df
Vandromme, Pieter
643a306a-ef96-4fd6-8c33-c773bfa9fc1a
d'Ovidio, Francesco
98150638-e3dc-4142-adcb-b13fee133748
Stemmann, Lars
27636c5e-60a5-47ed-a2dc-1da6a371e708
Rengarajan, R.
ef81c56b-ff42-4ab8-8c72-199977127f79
Soares, Melena
e47d03fe-cf4b-4544-af05-11c7714f7da3
González, Humberto E.
5d36d89a-ebd1-4117-807f-2ad943b021e5
Ebersbach, Friederike
00c810a1-6d7a-486f-92e6-3ba1934e812b
Lampitt, Richard S.
dfc3785c-fc7d-41fa-89ee-d0c6e27503ad
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Barnett, Bruce A.
f6ff6a15-291f-4ccf-8cf8-dc76049f4fa2
Smetacek, Victor
bb4657f5-c95d-4fcc-b568-75134ed16684
Naqvi, S. Wajih A.
b8e966b5-c3b5-4398-9057-56c0818f2673
Martin, Patrick
01ce1c59-3926-46c9-a556-fac39e0ee16b
van der Loeff, Michiel Rutgers
5cbd760d-b52b-46b7-8058-945ea9edfc62
Cassar, Nicolas
77fc58ca-3e20-44b5-b397-801ec4d8f5df
Vandromme, Pieter
643a306a-ef96-4fd6-8c33-c773bfa9fc1a
d'Ovidio, Francesco
98150638-e3dc-4142-adcb-b13fee133748
Stemmann, Lars
27636c5e-60a5-47ed-a2dc-1da6a371e708
Rengarajan, R.
ef81c56b-ff42-4ab8-8c72-199977127f79
Soares, Melena
e47d03fe-cf4b-4544-af05-11c7714f7da3
González, Humberto E.
5d36d89a-ebd1-4117-807f-2ad943b021e5
Ebersbach, Friederike
00c810a1-6d7a-486f-92e6-3ba1934e812b
Lampitt, Richard S.
dfc3785c-fc7d-41fa-89ee-d0c6e27503ad
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Barnett, Bruce A.
f6ff6a15-291f-4ccf-8cf8-dc76049f4fa2
Smetacek, Victor
bb4657f5-c95d-4fcc-b568-75134ed16684
Naqvi, S. Wajih A.
b8e966b5-c3b5-4398-9057-56c0818f2673

Martin, Patrick, van der Loeff, Michiel Rutgers, Cassar, Nicolas, Vandromme, Pieter, d'Ovidio, Francesco, Stemmann, Lars, Rengarajan, R., Soares, Melena, González, Humberto E., Ebersbach, Friederike, Lampitt, Richard S., Sanders, Richard, Barnett, Bruce A., Smetacek, Victor and Naqvi, S. Wajih A. (2013) Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX. Global Biogeochemical Cycles, 27 (3), 871-881. (doi:10.1002/gbc.20077).

Record type: Article

Abstract

A closed eddy core in the Subantarctic Atlantic Ocean was fertilized twice with two tons of iron (as FeSO 4), and the 300 km2 fertilized patch was studied for 39 days to test whether fertilization enhances downward particle flux into the deep ocean. Chlorophyll a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to ? 0.40. Silicic acid (<2 ?mol L1) limited diatoms, which contributed <10% of phytoplankton biomass. Copepods exerted high grazing pressure. This is the first study of particle flux out of an artificially fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch, estimated from O2:Ar ratios, averaged 21 mmol POC m2 d1, probably±20%. 234Th profiles implied constant export of ~6.3 mmol POC m2 d1 in the patch, similar to unfertilized waters. The difference between NCP and 234Th-derived export partly accumulated in the mixed layer and was partly remineralized between the mixed layer and 100 m. Neutrally buoyant sediment traps at 200 and 450 m inside and outside the patch caught mostly <1.1 mmol POC m2 d1, predominantly of fecal origin; flux did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.

This record has no associated files available for download.

More information

Published date: September 2013
Organisations: Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 359627
URI: http://eprints.soton.ac.uk/id/eprint/359627
ISSN: 0886-6236
PURE UUID: 1ba45615-72e9-4a72-9d3d-d5091c611811

Catalogue record

Date deposited: 06 Nov 2013 15:11
Last modified: 27 Apr 2022 10:59

Export record

Altmetrics

Contributors

Author: Patrick Martin
Author: Michiel Rutgers van der Loeff
Author: Nicolas Cassar
Author: Pieter Vandromme
Author: Francesco d'Ovidio
Author: Lars Stemmann
Author: R. Rengarajan
Author: Melena Soares
Author: Humberto E. González
Author: Friederike Ebersbach
Author: Richard S. Lampitt
Author: Richard Sanders
Author: Bruce A. Barnett
Author: Victor Smetacek
Author: S. Wajih A. Naqvi

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.

×