Iron Distribution in the Subtropical North Atlantic: The Pivotal Role of Colloidal Iron

Key Points Size‐fractionation reveals that colloidal iron is more important than soluble iron for distribution of dissolved iron in North Atlantic Colloidal iron is the predominantly active species at key supply and removal processes of the dissolved iron cycle Global comparison suggests that the colloidal iron fraction in mesopelagic zone is determined by the local lithogenic contribution The low availability of the essential micronutrient iron (Fe) in the ocean impacts the efficiency of the biological carbon pump, and hence, it is vital to elucidate its sources, sinks, and internal cycling. We present size‐fractionated dissolved Fe (dFe,