Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 21
Biogeosciences, 15, 6659-6684, 2018
https://doi.org/10.5194/bg-15-6659-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 6659-6684, 2018
https://doi.org/10.5194/bg-15-6659-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reviews and syntheses 09 Nov 2018

Reviews and syntheses | 09 Nov 2018

Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study

Stelios Myriokefalitakis1,a, Akinori Ito2, Maria Kanakidou3, Athanasios Nenes4, Maarten C. Krol1, Natalie M. Mahowald5, Rachel A. Scanza5, Douglas S. Hamilton5, Matthew S. Johnson6, Nicholas Meskhidze7, Jasper F. Kok8, Cecile Guieu9, Alex R. Baker10, Timothy D. Jickells10, Manmohan M. Sarin11, Srinivas Bikkina11, Rachel Shelley12, Andrew Bowie13,14, Morgane M. G. Perron13, and Robert A. Duce15 Stelios Myriokefalitakis et al.
  • 1Institute for Marine and Atmospheric Research (IMAU), Utrecht University, 3584 CC Utrecht, the Netherlands
  • 2Yokohama Institute for Earth Sciences, JAMSTEC, Yokohama, Kanagawa 236-0001, Japan
  • 3Environmental Chemical Processes Laboratory (ECPL), Department of Chemistry, University of Crete, 70013 Heraklion, Greece
  • 4School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • 5Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, USA
  • 6Earth Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
  • 7Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, USA
  • 8Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA
  • 9Laboratoire d'Océanographie de Villefranche (LOV), UMR7093, CNRS-INSU-Université Paris 6, Villefranche sur Mer, France
  • 10Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 11Geosciences Division, Physical Research Laboratory, Ahmedabad, India
  • 12Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, Florida 32306-4320, USA
  • 13Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 14Antarctic Climate & Ecosystems CRC, Hobart, Tasmania, Australia
  • 15Departments of Oceanography and Atmospheric Sciences, Texas A&M University, College Station, TX 77843, USA
  • anow at: Institute for Environmental Research & Sustainable Development (IERSD), National Observatory of Athens, 15236 Palea Penteli, Greece

Abstract. This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and atmospheric concentrations and the analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry transport (CTMs) and general circulation (GCMs) models participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, The Atmospheric Input of Chemicals to the Ocean. The global total Fe (TFe) emission strength in the models is equal to  ∼ 72Tg Fe yr−1 (38–134Tg Fe yr−1) from mineral dust sources and around 2.1Tg Fe yr−1 (1.8–2.7Tg Fe yr−1) from combustion processes (the sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3)Tg Fe yr−1, accounting for both mineral dust and combustion aerosols. The mean global deposition fluxes into the global ocean are estimated to be in the range of 10–30 and 0.2–0.4Tg Fe yr−1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3Tg Fe yr−1 for the multi-model ensemble model mean.

The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parameterizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicates that most models overestimate surface level TFe mass concentrations near dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe concentrations near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere ( ∼ 14), larger than that of the Southern Hemisphere ( ∼ 2.4) for the ensemble model mean. This model intercomparison and model–observation comparison study reveals two critical issues in LFe simulations that require further exploration: (1) the Fe-containing aerosol size distribution and (2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions.

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The first atmospheric iron (Fe) deposition model intercomparison is presented in this study, as a result of the deliberations of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP; http://www.gesamp.org/) Working Group 38. We conclude that model diversity over remote oceans reflects uncertainty in the Fe content parameterizations of dust aerosols, combustion aerosol emissions and the size distribution of transported aerosol Fe.
The first atmospheric iron (Fe) deposition model intercomparison is presented in this study, as...
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