Retrospective satellite ocean color analysis of purposeful and natural ocean iron fertilization |
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| Institution: | 1. Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902, USA;2. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA;1. Marine Research Institute and Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch, 7701 Cape Town, South Africa;2. South African Environmental Observation Network (SAEON), Egagasini Node, Private Bag X2, Roggebaai, 8012 Cape Town, South Africa;3. Department of Biodiversity and Conservation, Cape Peninsula University of Technology, PO Box 652, Cape Town 8000, South Africa;4. Ocean and Coastal Research, Department of Environmental Affairs, Private Bag X4390, Cape Town 8000, South Africa;1. School of Fisheries and Ocean Sciences, University of Alaska, 905 N. Koyukuk Drive, Fairbanks, AK 99775-7220, USA;2. Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland;3. Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, MA 02543, USA;4. National Oceanography Centre Southampton, European Way, Southampton SO14 3ZH, UK;5. National Oceanography Centre Southampton, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH UK;6. Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA;7. Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA;1. Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, PR China;2. State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, PR China;3. University of Chinese Academy of Sciences, Beijing, 100049, PR China;1. Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA, 92093-0227, USA;2. Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD, USA;3. CSIRO Oceans and Atmosphere, Castray Esplanade, Hobart, Tasmania, 7000, Australia;4. Department of Oceanography, University of Hawai''i at Manoa, Honolulu, HI, 96822, USA;5. Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Perth, WA, 6845, Australia;6. Sorbonne Université, CNRS, Laboratoire d’Océanographie de Villefranche, LOV, F-06230, Villefranche-sur-Mer, France;7. Environmental and Conservation Sciences, Murdoch University, Murdoch, 6150, Western Australia, Australia |
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| Abstract: | Significant effort has been invested in understanding the role of iron in marine ecosystems over the past few decades. What began as shipboard amendment experiments quickly grew into a succession of in situ, mesoscale ocean iron fertilization (OIF) experiments carried out in all three high nutrient low chlorophyll (HNLC) regions of the world ocean. Dedicated process studies have also looked at regions of the ocean that are seasonally exposed to iron-replete conditions as natural OIF experiments. However, one problem common to many OIF experiments is determination of biological response beyond the duration of the experiment (typically<1 month). Satellite-derived products have been used to address this shortcoming with some success, but thus far, have been limited snapshots of a single parameter, chlorophyll. Here, we investigate phytoplankton responses to OIF in both purposeful and naturally iron enriched systems using estimates of chlorophyll (Chl), phytoplankton carbon biomass (Cphyto), their ratio (Chl:Cphyto) and two fluorescence indices, fluorescence per unit chlorophyll (FLH:Chl) and the chlorophyll fluorescence efficiency (?f). These quantities allow partitioning of the biological response to OIF into that due to changes in biomass and that due to phytoplankton physiology. We find that relative increases in Chl (～10–20x) following OIF far exceed increases in Cphyto (<4–5x), suggesting that a significant fraction of the observed Chl increase is associated with physiological adjustment to increased growth rates, photoacclimation, and floristic shifts in the phytoplankton community. Further, a consistent pattern of decreased satellite fluorescence efficiency (FLH:Chl or ?f) following OIF is observed that is in agreement with current understanding of phytoplankton physiological responses to relief from iron stress. The current study extends our ability to retrieve phytoplankton physiology from space-based sensors, strengthens the link between satellite fluorescence and iron availability, and shows that satellite ocean color analyses provide a unique tool for monitoring OIF experiments. |
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