Deep-sea hydrothermal venting is an important source of dissolved iron (dFe) to the oceans. The species and isotope compositions of iron in hydrothermal plumes are crucial for understanding the contribution of hydrothermal venting to the oceanic Fe inventory. Our researches revealed that dissolved Fe (dFe) constituted a significant portion of total Fe (tFe), which might be related to the existence of organic Fe complexes (FeL), as well as colloidal Fe oxyhydroxides and sulfides. The FeL constituted ~30% of the DFe, which may be an explanation for long-range transport of hydrothermal plumes. We investigated the Fe isotope compositions in hydrothermal plumes in the Northeast Lau Basin, Southwest Pacific Ocean. The results suggest δ⁵⁶tFe variation in plumes is related to the loss of particulate Fe-sulfides or Fe-oxyhydroxides (FeOOH), both of which are dependent on the H₂S concentrations and Fe/H₂S in the source hydrothermal fluids. δ⁵⁶dFe compositions in the hydrothermal plumes increase during plume dispersal/dilution. The reasons may be ascribed to the organic Fe complexes (FeL) and colloidal FeOOH in the dissolved phase. We built a Rayleigh distillation model to describe the Fe isotope evolution in hydrothermal plumes, which can explain the observed Fe isotope compositions in hydrothermal plumes.

iron species, ron isotopes, organic ligands, hydrothermal plume