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Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment

Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment
Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment
Comparison of eight iron experiments shows that maximum Chl a, the maximum DIC removal, and the overall DIC/ Fe efficiency all scale inversely with depth of the wind mixed layer (WML) defining the light environment. Moreover, lateral patch dilution, sea surface irradiance, temperature, and grazing play additional roles. The Southern Ocean experiments were most influenced by very deep WMLs. In contrast, light conditions were most favorable during SEEDS and SERIES as well as during IronEx-2. The two extreme experiments, EisenEx and SEEDS, can be linked via EisenEx bottle incubations with shallower simulated WML depth. Large diatoms always benefit the most from Fe addition, where a remarkably small group of thriving diatom species is dominated by universal response of Pseudo-nitzschia spp. Significant response of these moderate ( 10 - 30 mu m), medium ( 30 - 60 mu m), and large (> 60 mu m) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of "dissolved'' Fe ( filtrate < 0.2 mu m) maintained during an experiment determines the dominant diatom size class. However, this is further complicated by continuous transfer of original truly dissolved reduced Fe(II) into the colloidal pool, which may constitute some 75% of the "dissolved'' pool. Depth integration of carbon inventory changes partly compensates the adverse effects of a deep WML due to its greater integration depths, decreasing the differences in responses between the eight experiments. About half of depth-integrated overall primary productivity is reflected in a decrease of DIC. The overall C/Fe efficiency of DIC uptake is DIC/Fe similar to 5600 for all eight experiments. The increase of particulate organic carbon is about a quarter of the primary production, suggesting food web losses for the other three quarters. Replenishment of DIC by air/sea exchange tends to be a minor few percent of primary CO2 fixation but will continue well after observations have stopped. Export of carbon into deeper waters is difficult to assess and is until now firmly proven and quite modest in only two experiments.
equatorial Pacific Ocean, release experiment soiree, sub-Arctic Pacific, Austral spring 1992, open Southern Ocean, phytoplankton growth, enrichment experiment, experiment SOFEX, sulfur hexafluoride, carbon dioxide
0148-0227
C09S16
de Baar, Hein J.W.
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Tsuda, Atsushi
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Bakker, Dorothee C.E.
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Barber, Richard T.
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Brzezinski, Mark A.
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Boye, Marie
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Croot, Peter L.
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Gervais, Frank
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Law, Cliff S.
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Marchetti, Adrian
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Millero, Frank J.
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Nishioka, Jun
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Nojiri, Yukihiro
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van Oijen, Tim
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Riebesell, Ulf
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Saito, Hiroaki
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de Baar, Hein J.W.
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Coale, Kenneth H.
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Landry, Michael R.
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Tsuda, Atsushi
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Assmy, Philipp
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Law, Cliff S.
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Levasseur, Maurice
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Marchetti, Adrian
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Millero, Frank J.
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Nishioka, Jun
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van Oijen, Tim
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Riebesell, Ulf
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Saito, Hiroaki
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Takeda, Shigenobu
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Veldhuis, Marcel J.W.
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Waite, Anya M.
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Wong, Chi-Shing
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de Baar, Hein J.W., Boyd, Philip W., Coale, Kenneth H., Landry, Michael R., Tsuda, Atsushi, Assmy, Philipp, Bakker, Dorothee C.E., Bozec, Yann, Barber, Richard T., Brzezinski, Mark A., Buesseler, Ken O., Boye, Marie, Croot, Peter L., Gervais, Frank, Gorbunov, Maxim Y., Harrison, Paul J., Hiscock, William T., Laan, Patrick, Lancelot, Christiane, Law, Cliff S., Levasseur, Maurice, Marchetti, Adrian, Millero, Frank J., Nishioka, Jun, Nojiri, Yukihiro, van Oijen, Tim, Riebesell, Ulf, Rijkenberg, Micha J.A., Saito, Hiroaki, Takeda, Shigenobu, Timmermans, Klaas R., Veldhuis, Marcel J.W., Waite, Anya M. and Wong, Chi-Shing (2005) Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment. Journal of Geophysical Research, 110 (C9), C09S16. (doi:10.1029/2004JC002601).

Record type: Article

Abstract

Comparison of eight iron experiments shows that maximum Chl a, the maximum DIC removal, and the overall DIC/ Fe efficiency all scale inversely with depth of the wind mixed layer (WML) defining the light environment. Moreover, lateral patch dilution, sea surface irradiance, temperature, and grazing play additional roles. The Southern Ocean experiments were most influenced by very deep WMLs. In contrast, light conditions were most favorable during SEEDS and SERIES as well as during IronEx-2. The two extreme experiments, EisenEx and SEEDS, can be linked via EisenEx bottle incubations with shallower simulated WML depth. Large diatoms always benefit the most from Fe addition, where a remarkably small group of thriving diatom species is dominated by universal response of Pseudo-nitzschia spp. Significant response of these moderate ( 10 - 30 mu m), medium ( 30 - 60 mu m), and large (> 60 mu m) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of "dissolved'' Fe ( filtrate < 0.2 mu m) maintained during an experiment determines the dominant diatom size class. However, this is further complicated by continuous transfer of original truly dissolved reduced Fe(II) into the colloidal pool, which may constitute some 75% of the "dissolved'' pool. Depth integration of carbon inventory changes partly compensates the adverse effects of a deep WML due to its greater integration depths, decreasing the differences in responses between the eight experiments. About half of depth-integrated overall primary productivity is reflected in a decrease of DIC. The overall C/Fe efficiency of DIC uptake is DIC/Fe similar to 5600 for all eight experiments. The increase of particulate organic carbon is about a quarter of the primary production, suggesting food web losses for the other three quarters. Replenishment of DIC by air/sea exchange tends to be a minor few percent of primary CO2 fixation but will continue well after observations have stopped. Export of carbon into deeper waters is difficult to assess and is until now firmly proven and quite modest in only two experiments.

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More information

Published date: 2005
Keywords: equatorial Pacific Ocean, release experiment soiree, sub-Arctic Pacific, Austral spring 1992, open Southern Ocean, phytoplankton growth, enrichment experiment, experiment SOFEX, sulfur hexafluoride, carbon dioxide

Identifiers

Local EPrints ID: 41431
URI: https://eprints.soton.ac.uk/id/eprint/41431
ISSN: 0148-0227
PURE UUID: 8f8be853-245d-4219-accc-4bd2c61e11ee

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Date deposited: 12 Sep 2006
Last modified: 15 Jul 2019 18:57

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Contributors

Author: Hein J.W. de Baar
Author: Philip W. Boyd
Author: Kenneth H. Coale
Author: Michael R. Landry
Author: Atsushi Tsuda
Author: Philipp Assmy
Author: Dorothee C.E. Bakker
Author: Yann Bozec
Author: Richard T. Barber
Author: Mark A. Brzezinski
Author: Ken O. Buesseler
Author: Marie Boye
Author: Peter L. Croot
Author: Frank Gervais
Author: Maxim Y. Gorbunov
Author: Paul J. Harrison
Author: William T. Hiscock
Author: Patrick Laan
Author: Christiane Lancelot
Author: Cliff S. Law
Author: Maurice Levasseur
Author: Adrian Marchetti
Author: Frank J. Millero
Author: Jun Nishioka
Author: Yukihiro Nojiri
Author: Tim van Oijen
Author: Ulf Riebesell
Author: Micha J.A. Rijkenberg
Author: Hiroaki Saito
Author: Shigenobu Takeda
Author: Klaas R. Timmermans
Author: Marcel J.W. Veldhuis
Author: Anya M. Waite
Author: Chi-Shing Wong

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