A multi-modal approach to measuring particulate iron speciation in buoyant hydrothermal plumes

Processes active within buoyant hydrothermal plumes are expected to modulate the flux of elements, such as Fe, deep ocean; however, they yet be described in a comprehensive manner through observations or models. In this study, we compare observed particulate Fe (pFe) speciation with thermodynamic (equilibrium) reaction path modeling for three vent fields Eastern Lau Spreading Center (ELSC). At each site, particles were collected from rising portion using situ filtration Remotely Operated Vehicle. Filter bound analyzed by synchrotron micro-probe X-ray fluorescence mapping (XRF), diffraction (XRD), XRF spectroscopy, and absorption near edge structure (XANES) spectroscopy at 1 s edge, well XRF-based chemical Fe. For ELSC, diversity solid-state chemistry was high, poorly crystalline, meta-stable phases common. We demonstrate that fully describe crystalline-to-noncrystalline character plume pFe, multi-modal XRD-XANES analytical approach is needed. found an equilibrium worked pyrite but performed important families namely (oxyhydr)oxides monosulfides. Based on our findings, recommend future field expeditions strategically explore sites representing site-specific conditions better capture full range processes plumes. also development kinetic models, expansion databases reflect composition These steps should allow oceanographers understand controlling enough create realistic models fluxes ocean.