Deep-sea hydrothermal vents are a significant source of dissolved metals to the global oceans, producing midwater plumes enriched in metals that are transported thousands of kilometers from the vent source. Extensive particle precipitation upon emission of hydrothermal fluids, due to temperature and pH changes during mixing with ambient seawater, controls metal speciation and the magnitude of metal export. Here, we document the formation and spatial distribution of metal sulfide particles, including pyrite (nano)particles, within the first meter of buoyant plumes from three high-temperature hydrothermal vents at the East Pacific Rise (9°50’ N). We observe a zone of particle settling 10 – 20 cm from the orifice, indicated by the stable sulfur isotope distribution of sulphide in the plume; however, we also demonstrate that nanoparticulate pyrite (FeS2) is not removed from the plume and can account for over half of the filtered Fe (≤ 0.2 µm) up to one meter from the vent orifice. The persistence of nanoparticulate pyritic Fe beyond the first meter demonstrates that it is an important mechanism for near-vent Fe stabilisation that may further allow transport of Fe to midwater plumes, and highlights the potential role of nanoparticles in element transport.
