Hydrothermally sourced dissolved metals have been recorded in all ocean basins. In the oceans' largest known hydrothermal plume, extending westwards across the Pacific from the Southern East Pacific Rise, dissolved iron and manganese were shown by the GEOTRACES program to be transported halfway across the Pacific. Here, we report that particulate iron and manganese in the same plume also exceed background concentrations, even 4,000 km from the vent source. Both dissolved and particulate iron deepen by more than 350 m relative to 3 He-a non-reactive tracer of hydrothermal input-crossing isopycnals. Manganese shows no similar descent. Individual plume particle analyses indicate that particulate iron occurs within low-density organic matrices, consistent with its slow sinking rate of 5-10 m yr â '1. Chemical speciation and isotopic composition analyses reveal that particulate iron consists of Fe(III) oxyhydroxides, whereas dissolved iron consists of nanoparticulate Fe(III) oxyhydroxides and an organically complexed iron phase. The descent of plume-dissolved iron is best explained by reversible exchange onto slowly sinking particles, probably mediated by organic compounds binding iron. We suggest that in ocean regimes with high particulate iron loadings, dissolved iron fluxes may depend on the balance between stabilization in the dissolved phase and the reversibility of exchange onto sinking particles.
Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, United States; Department of Oceanography, Texas AandM University, College Station, TX, United States; Department of Earth Sciences, University of Southern California, Los Angeles, CA, United States; Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC, United States; Skidaway Institute of Oceanography, University of Georgia, Savannah, GA, United States; Department of Earth Sciences, University of Minnesota-Twin Cities, Minneapolis, MN, United States; Department of Soil Water, and Climate, University of Minnesota-Twin Cities, St Paul, MN, United States; Department of Earth and Ocean Sciences, National University of Ireland, Galway, Ireland; Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States
Recommended Citation:
Fitzsimmons J.N.,John S.G.,Marsay C.M.,et al. Iron persistence in a distal hydrothermal plume supported by dissolved-particulate exchange[J]. Nature Geoscience,2017-01-01,10(3)