The objective of this proposal is to organize and host a workshop that will address the most urgent open science questions related to biogeochemical cycling of iron (Fe) in the Earth System. The physicochemical speciation of Fe at the atmosphere-ocean interface and its cycling between the two oxidation states in soluble, colloidal, dissolved, amorphous, and crystalline forms, in the presence/absence of atmospheric/oceanic organic compounds and sunlight is one of the most uncertain components of Fe biogeochemical cycling. Yet, it received less attention than other “pure” oceanic or atmospheric processes, largely due to historic division of the related fields. Moreover, there are some exciting results in both atmospheric and oceanic fields that are often mutually beneficial, but not readily shared. This can lead to duplication of work, which in the best case delays the progress of finding the measurement and modeling solutions to handling iron speciation at the atmosphere-ocean interface. A small workshop will facilitate interactive discussion, often lost in big meetings. Participation in the workshop will be predominately by invitation. During the workshop, all the participants working on different parts of iron biogeochemistry (in the atmosphere and the oceans) and different working groups (i.e., FeMIP, GESAMP, ACE, etc.) will be engaged to explore what simultaneous information would be needed and what steps need to be taken to acquire such information, gain insight, and answer the most critical questions. One of the major goals of the workshop is to bring together established scientists and young researchers with new and different perspectives. To achieve this goal and to provide opportunities for professional interactions in a focused and productive forum, one third of invited researchers will be early career scientists (PhD students, postdoctoral researchers and young research scientists who received their PhD after 2010).

Motivation: Earth System Models (ESMs) now pay particular attention to interactions between the atmosphere and the ocean ecosystems, in response to the highlighted need for improved representation of climate forcing and feedbacks. These interactions have implications on trace gas exchange, bidirectional flux of particulates, and the overall global energy budget. Today all global ocean biogeochemical cycling models agree that accurate characterization of the ocean’s biological, chemical, and physical processes requires quantitative knowledge of atmospheric sources of aerosol soluble iron (sol-Fe), the fraction of total Fe that contributes to the dissolved Fe (DFe) inventory of the ocean. In addition to the direct forcing of climate through its effect on ocean productivity and atmospheric CO2 uptake, the atmospheric deposition of sol-Fe has been suggested to affect ocean ecosystem diversity and, as a result, climate feedbacks. Detailed atmospheric models for the delivery of sol-Fe from different aerosol sources (mineral dust, combustion, biomass burning), to the open oceans have been developed. However, mechanistic treatments of sol-Fe interaction with atmospheric dissolved organic matter or organics found in the ocean surface microlayer are still missing. Progress has been made in the treatment of different forms of DFe in ocean biogeochemical models, but especially a kinetic description of the processes (redox, organic complexation) that further affect iron solubility after deposition is still rudimentary. Without identifying and accurately describing Fe biogeochemical processes operating at the atmosphere-ocean boundary, ESM results cannot be used for confident projections of human induced effects on the carbon cycle and climate, or for exploring the effects of atmospheric nutrient deposition on phytoplankton abundance and diversity.