Anthropogenic Iron Invasion into the Ocean: Results from the East Sea (Japan Sea)

Anthropogeniciron from fossil-fuel combustion significantlyimpacts the bioavailable iron pool of the aerosol and seawater inthe East Sea (Japan Sea). Iron (Fe) is an essential micronutrient for phytoplanktongrowth,and its availability limits primary production in half of the globalocean. Traditionally, atmospheric input of natural mineral dust hasbeen considered as a main source of Fe in the surface ocean. However,here we show that about 45% of the water-soluble Fe in aerosols collectedover the East Sea (Japan Sea) is anthropogenic, which originates mainlyfrom heavy fuel oil combustion, based on the analyses of various chemicaltracers (Al, K, V, Ni, Pb, and Pb-210). It is striking thata tiny quantity of oil, less than 1% of the aerosols in mass, canconstitute the majority of water-soluble Fe in aerosols due to itshigh Fe solubility. Furthermore, we show that a quarter of dissolvedFe in the East Sea is anthropogenic using a Pb-210-basedscavenging model. Since this sea is almost fully enclosed (200-3000m) and located at the forefront of the Asian human footprint, ourresults provide an insight that the marine Fe cycle may be alreadyperturbed by human activities.