Synthesis of iron fertilization experiments: From the iron age in the age of enlightenment

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

Research output: Contribution to journalReview articlepeer-review

507 Scopus citations


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 μm), medium (30-60 μm), and large (>60 μm) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of "dissolved" Fe (filtrate < 0.2 μm) 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 ∼ 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.

Original languageEnglish (US)
Article numberC09S16
Pages (from-to)1-24
Number of pages24
JournalJournal of Geophysical Research C: Oceans
Issue number9
StatePublished - Sep 8 2005
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology


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