Isotopic signature of dissolved iron delivered to the Southern Ocean from hydrothermal vents in the East Scotia Sea

• It has recently been demonstrated that hydrothermal vents are an important source of dissolved Fe (dFe) to the Southern Ocean. The isotopic composition (delta Fe-56) of dFe in vent fluids appears to be distinct from other sources of dFe to the deep ocean, but the evolution of delta Fe-56 during mixing between vent fluids and seawater is poorly constrained. Here we present the evolution of delta Fe-56 for dFe in hydrothermal fluids and dispersing plumes from two sites in the East Scotia Sea. We show that delta Fe-56 values in the buoyant plume are distinctly lower (as low as -1.19 parts per thousand) than the hydrothermal fluids (-0.29 parts per thousand), attributed to (1) precipitation of Fe sulfides in the early stages of mixing, and (2) partial oxidation of Fe(II) to Fe(III), >55% of which subsequently precipitates as Fe oxyhydroxides. By contrast, the delta Fe-56 signature of stabilized dFe in the neutrally buoyant plume is -0.3 parts per thousand to -0.5 parts per thousand. This cannot be explained by continued dilution of the buoyant plume with background seawater; rather, we suggest that isotope fractionation of dFe occurs during plume dilution due to Fe ligand complexation and exchange with labile particulate Fe. The delta Fe-56 signature of stabilized hydrothermal dFe in the East Scotia Sea is distinct from background seawater and may be used to quantify the hydrothermal dFe input to the ocean interior.

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NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

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