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Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Marine Biology, University of Groningen, Haren, Netherlands
National Institute of Water and Atmospheric Research, Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand
Moss Landing Marine Laboratories, Moss Landing, California, USA
Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
University of Tokyo, Ocean Research Institute, Tokyo, Japan
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
School of Environmental Sciences, University of East Anglia, Norwich, UK
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Nicholas School of the Environment and Earth Sciences, Duke University, Beaufort, North Carolina, USA
Marine Science Institute and Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, California, USA
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Marine Biology, University of Groningen, Haren, Netherlands
Université de Bretagne Occidentale, Brest, France
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Leibniz Institut für Meereswissenschaften, IFM-GEOMAR, Kiel, Germany
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
Atmospheric, Marine and Coastal Environment Program, Hong Kong University of Science and Technology, Hong Kong, China
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Ecologie des Systemes Aquatiques, Université Libre de Bruxelles, Brussels, Belgium
National Institute of Water and Atmospheric Research, Wellington, New Zealand
Département de Biologie (Québec-Océan), Université Laval, Quebec, Canada
University of British Columbia, Vancouver, British Columbia, Canada
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA
Central Research Institute of Electric Power Industry, Chiba, Japan
National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
Marine Biology, University of Groningen, Haren, Netherlands
Leibniz Institut für Meereswissenschaften, IFM-GEOMAR, Kiel, Germany
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Marine Biology, University of Groningen, Haren, Netherlands
Tohoku National Fisheries Research Institute, Miyagi, Japan
Department of Aquatic Bioscience, University of Tokyo, Tokyo, Japan
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Royal Netherlands Institute for Sea Research, Isle of Texel, Netherlands
Centre for Water Research, University of Western Australia, Crawley, Australia
Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, British Columbia, Canada
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.
Received 16 July 2004; accepted 14 July 2005; published 28 September 2005.
Citation: (2005), Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment, J. Geophys. Res., 110, C09S16, doi:10.1029/2004JC002601.
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