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Hydrothermal vents are a source of many trace metals to the oceans. Compared to mid-ocean ridges, hydrothermal vent systems at arcs occur in shallower water depth and are much more diverse in fluid composition, resulting in highly variable water column trace metal concentrations. However, only few studies have focused on trace metal dynamics in hydrothermal plumes at volcanic arcs. During R/V Sonne cruise SO253 in 2016/2017, hydrothermal plumes from two hydrothermally active submarine volcanoes along the Kermadec arc in the Southwest Pacific Ocean were sampled: (1) Macauley, a magmatic dominated vent site located in water depths between 300 and 680 m, and (2) Brothers, located between 1,200 and 1,600 m water depth, where hydrothermalism influenced by water rock interactions and magmatically influenced vent sites occur near each other. Surface currents estimated from satellite-altimeter derived currents and direct measurements at the sites using lowered acoustic Doppler current profilers indicate the oceanic regime is dominated by mesoscale eddies. At both volcanoes, results indicated strong plumes of dissolved trace metals, notably Mn, Fe, Co, Ni, Cu, Zn, Cd, La, and Pb, some of which are essential micronutrients. Dissolved metal concentrations commonly decreased with distance from the vents, as to be expected, however, certain element/Fe ratios increased, suggesting a higher solubility of these elements and/or their stronger stabilization (e.g., for Zn compared to Fe). Our data indicate that at the magmatically influenced Macauley and Brothers cone sites, the transport of trace metals is strongly controlled by sulfide nanoparticles, while at the Brothers NW caldera wall site iron oxyhydroxides seem to dominate the trace metal transport over sulfides. Solution stabilization of trace metals by organic complexation appears to compete with particle adsorption processes. As well as extending the generally sparse data set for hydrothermal plumes at volcanic arc systems more...

Hydrothermal venting is an important transfer process of energy and elements between the Earth’s solid material and the oceans. Compared to mid-ocean-ridge hydrothermal vent fields, those at intra-oceanic island arcs are typically in shallower water depth and have a more variable geochemical fluid composition. Biologically essential trace elements (such as Fe and Mn) are generally elevated in fluids of both deep and shallow hydrothermal vent fields, while vents at shallower water depth influence the photic zone more directly and thus are potentially more relevant for marine primary productivity. However, fluid flux estimations of island arc hydrothermal systems into the surrounding water column are scarce. This study (I) presents a method based on short-lived radium isotopes to estimate submarine hydrothermal discharge (SHD), (II) applies this method at Brothers volcano in the southern Kermadec arc, located northeast of New Zealand, and (III) gives dissolved Fe, Mn and He isotope flux estimates for the Earth´s longest intra-oceanic island arc, the Kermadec arc. The comparison between measured inert He isotope concentrations in the plume with calculated concentrations based on Ra isotopes matched reasonably well, which supports the use of a Ra-based discharge model. Overall, this study represents a novel approach to assess fluid and thus trace element fluxes from one hydrothermal vent field, which can be applied in future studies on various hydrothermal systems to improve geochemical models of element cycling in the ocean. more...