Hydrothermal plume - particle fluxes at 13N on the East Pacific Rise

We have investigated the geochemical flux to sediment traps deployed close to the Totem vent site, 13°N EPR. An important emphasis has been to investigate what proportion of this settling flux derives from direct co-precipitation of vent-fluid material as polymetallic sulphides and what proportion is in the form of Fe oxyhydroxide material which not only co-precipitates vent-fluid metals but can also scavenge dissolved material from seawater. Mass fluxes and major element compositions (Fe, S, Al, Mn, CaCO3 and Corg) for our near vent samples compare well with results from previously reported Pacific hydrothermal sediment trap studies, both at this site and on the Endeavour Ridge. Our samples record large fluxes of Cu, Zn and Pb, as well as V and P, all of which are in excess over typical open-ocean trap values. If P and V are transported to the traps as sinking Fe-oxyhydroxide material from the neutrally buoyant plume, we calculate that 10–20% of the Fe entering the near vent traps occurs as oxidised material with the remaining 80–90% being supplied by polymetallic sulphides. Shale-normalised REE distribution patterns for near-vent trap samples are similar to those for local vent fluids and sulphidic sediments. Detailed mass balance calculations, however, reveal evidence for additional input from hydrothermal Fe-oxyhydroxide material with a scavenged REE composition that is less "evolved" than that reported for local neutrally buoyant plume particles. U fluxes into the near vent traps are high and consistent with uptake by sulphides. 210Pb fluxes are also high and appear dominated by co-precipitation direct from vent-fluids as Pb-sulphides. In contrast, Fe-oxyhydroxide scavenging from seawater can account for the entire 230Th and 232Th fluxes reported. If the scavenging processes identified here were similarly active in neutrally buoyant plumes, we would predict hydrothermal scavenging to impact ocean biogeochemical cycles significantly, e.g. causing removal of ca. 10% of the dissolved 230Th production from the deep water column, out to a distance of ca. 10–100 km off-axis, along the entire 60,000 km global ridge-crest