AGU’s Leadership Development/Governance Committee recaps the timing, participation, and other details of the organization’s recently completed 2020 leadership election.

Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity.

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 ∼ 72 Tg Fe yr−1 (38–134 Tg Fe yr−1) from mineral dust sources and around 2.1 Tg Fe yr−1 (1.8–2.7 Tg 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 0.2–0.4 Tg Fe yr−1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3 Tg 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.

(1) JAMSTEC, Yokohama, Japan (akinorii@jamstec.go.jp), (2) Utrecht Univ., Utrecht, The Netherlands, (3) Univ. of Crete, Heraklion, Greece, (4) Cornell Univ., Ithaca, USA, (5) Univ. of East Anglia, Norwich, UK, (6) Physical Research Laboratory, Ahmedabad, India, (7) Stockholm Univ., Stockholm, Sweden, (8) Rutgers Univ., Newark, USA, (9) Florida State Univ., Tallahassee, USA, (10) Univ. of Georgia, Savannah, USA, (11) Univ. of Tasmania, Tasmania, Australia, (12) North Carolina State Univ., Raleigh, USA, (13) NASA Ames Research Center, Mountain View, USA, (14) Argonne National Laboratory, Argonne, USA„ (15) Texas AM Univ., College Station, USA

Abstract. This work reports on the current status of global modelling of iron (Fe) deposition fluxes and atmospheric concentrations and 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 have 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) emissions strength in the models is equal to ~ 72 Tg-Fe yr−1 (38–134 Tg-Fe yr−1) from mineral dust sources and around 2.1 Tg-Fe yr−1 (1.8–2.7 Tg-Fe yr−1) from combustion processes (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 mineral dust and combustion aerosols together. The multi model ensemble global TFe and LFe deposition fluxes into the global ocean are calculated to be ~ 15 Tg-Fe yr−1 and ~ 0.3 Tg-Fe yr−1, respectively. 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 parametrizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicate that most models overestimate surface level TFe mass concentrations near the 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 loading near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (~ 14), larger than 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.

AGU's Leadership Development/Governance Committee recaps the timing, participation, and other details of the organization's recently completed 2018 leadership election.

a) b) c) d) Figure S1: Fe content (%) in mineral dust emissions, taken into account (a) CAM4, (b) GEOS-Chem, (c) IMPACT and (d) TM4-ECPL.The global mean value for each model is also provided in the title.

We report a new synthesis of best estimates of the inputs of fixed nitrogen to the world ocean via atmospheric deposition and compare this to fluvial inputs and dinitrogen fixation. We evaluate the scale of human perturbation of these fluxes. Fluvial inputs dominate inputs to the continental shelf, and we estimate that about 75% of this fluvial nitrogen escapes from the shelf to the open ocean. Biological dinitrogen fixation is the main external source of nitrogen to the open ocean, i.e., beyond the continental shelf. Atmospheric deposition is the primary mechanism by which land-based nitrogen inputs, and hence human perturbations of the nitrogen cycle, reach the open ocean. We estimate that anthropogenic inputs are currently leading to an increase in overall ocean carbon sequestration of similar to 0.4% (equivalent to an uptake of 0.15 Pg Cyr(-1) and less than the Duce et al. (2008) estimate). The resulting reduction in climate change forcing from this ocean CO2 uptake is offset to a small extent by an increase in ocean N2O emissions. We identify four important feedbacks in the ocean atmosphere nitrogen system that need to be better quantified to improve our understanding of the perturbation of ocean biogeochemistry by atmospheric nitrogen inputs. These feedbacks are recycling of (1) ammonia and (2) organic nitrogen from the ocean to the atmosphere and back, (3) the suppression of nitrogen fixation by increased nitrogen concentrations in surface waters from atmospheric deposition, and (4) increased loss of nitrogen from the ocean by denitrification due to increased productivity stimulated by atmospheric inputs.

70013, Greece 10 Department of Oceanography, University of Cape Town, South Africa. 11 Department of Geography, University of California at Los Angeles, California, USA 12 European Commission, Joint Research Centre, Ispra, Italy 13 Center for International Collaboration, Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan 14 Geosciences Division, Physical Research Laboratory, Ahmedabad, 380009, India 15 Departments of Oceanography and Atmospheric Sciences, Texas A&M University, College Station, Texas, USA 16 Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA 17 Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA 18 Universities Space Research Association, Columbia, MD, USA 19 NCAR Earth System Laboratory, National Center for Atmospheric Research, Boulder, CO, USA 20 Research Center for Environmental Changes, Academia Sinica, Nankang, Taipei, Taiwan 21 Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida, USA 22 now at IMAU, University of Utrecht, 3584 CC Utrecht, Netherlands 23 now at School of Physics, Astronomy and Maths, University of Hertfordshire, Hatfield, UK 24 * Deceased 10 October 2014 25

Knauss, an oceanographer who fiercely advocated for national and global marine initiatives, helped to develop many iconic programs and institutions that are key parts of oceanography today.