Recent studies have shown that a significant proportion of hydrothermal iron (Fe) is stabilized in the dissolved phase (dFe, <0.2 μm) with iron-binding organic ligands and as nano-particles in the colloidal size fraction (0.02-0.2 μm), that can be transported into the deep ocean away from vent fields (e.g., Hawkes et al., 2013). The isotopic composition of Fe can help us understand the processes occurring during vent fluid dilution as it mixes with seawater. Here we present the first results on δ56Fe (relative to 54Fe and IRMM-014) in the dissolved phase of dispersing hydrothermal plumes in the East Scotia Sea, Southern Ocean. Our results show that the isotopic composition of Fe undergoes significant changes throughout plume dilution. The δ56dFe in hydrothermal plumes becomes gradually higher during dispersal from the buoyant towards the neutrally buoyant plume. The remaining stabilized δ56dFe signature supplied by ESS hydrothermal high-temperature vents is -0.3 to -0.5 ‰. This isotopic signature is sufficiently distinct to detect and trace hydrothermally derived dissolved iron in the deep ocean. During this talk I will discuss several geochemical processes that may explain the observed trends in the Fe isotopic composition.
Hawkes, J. A., Connelly, D. P., Gledhill, M., and Achterberg, E. P., 2013, The stabilisation and transportation of dissolved iron from high temperature hydrothermal vent systems: Earth and Planetary Science Letters, v. 375, no. 0, p. 280-290.