ALBERT

Description: Calculated end-member compositions of hydrothermal fluids (for samples that have at least ≥ 85 % end-member) from Haungaroa, Brothers Upper Caldera and NW Caldera Wall, Kermadec intraoceanic arc. Ambient background seawater concentrations are given for comparison.

Description: Rare Earth Element and yttrium (REY) concentrations measured with ICP-MS in hydrothermal fluids from the Kermadec intraoceanic arc. Seawater from 1000 m water depth, values for SW are * 100 (SW data from Alibo and Nozaki (1999; doi:10.1016/S0016-7037(98)00279-8)).

Description: Comparison of Brothers hydrothermal fluid composition collected by de Ronde et al. (2011; doi:10.1007/s00126-011-0345-8) with data collected during this study. In this study, only samples taken with IGT and Major samplers with end-member concentrations greater than 50% are shown. The three samples from the Upper Caldera Site are not included within this data set.

Description: 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 for trace metals and nutrients: (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.

Description: Overview of all fluid samples collected during SO253 along the Kermadec intraoceanic arc together with parameters that were analyzed directly onboard.Fe were determined by a visual Fe CHEMets© field kit.

Description: Major, minor and trace element concentrations measured with ICP-OES, ICP-MS and data for SO42- in hydrothermal fluids from the Kermadec intraoceanic arc.

Description: Hydrothermal vents at the seafloor release large volumes of metal-rich fluids into the ocean. Some of these metals are biologically essential (such as Fe), while others may be toxic (e.g. Cu). Organisms living at these habitats produce small organic molecules, ligands that are able to form complexes with different metals, to either enhance their bioavailability or to decrease their toxicity. While some deep-sea vents have been studied with respect to metal complexation, comparable studies at shallow marine hydrothermal vent systems are rather rare. In this study, total dissolved Cu concentrations ([Cu]T) and corresponding Cu binding ligand concentrations ([L]Cu) at the shallow water hydrothermal vent fields off the coast of Milos (Greece), Dominica (Lesser Antilles) and the Bay of Plenty (New Zealand) were examined by a voltammetric ligand titration, using competitive ligand equilibration-adsorptive stripping voltammetry (CLE-AdCSV). Milos, Dominica and the Bay of Plenty are three very different environments and our data show that they are relatively depleted in total dissolved Cu, compared to deep-sea hydrothermal vents where [Cu]T and [L]Cu concentrations up to 400 nM and 4000 nM have been found, respectively. In this data set, [Cu]T rises up to 21.53 nM, however, most samples are in the range of 0.5 nM-3 nM. [L]Cu varies between 2.07 nM and 23.9 nM, with one exception, reaching 56.8 nM. Conditional stability constants (Log K) range between 11.57 and 14.01. Assuming that the three investigated sites are representative for shallow marine hydrothermal vents, the Cu-flux into the ocean due to complexation appears to be relatively low compared to deep-sea systems. Our data indicate a stable complexation of Cu in most cases, which may lower the toxic effect of Cu on these mixed photic-chemosynthetic communities. However one pore water sample from Dominica showed an excess [Cu]T over [L]Cu, which would create a highly toxic environment for most marine organisms. We further show that ligand-Cu ratios and complex stability constants are in a similar range as the ones at deep-sea vents, which may indicate similar complexation parameters and processes at shallow and deep-sea hydrothermal vents.

Description: Hydrothermal vent fluids are highly enriched in iron (Fe) compared to ambient seawater, and organic ligands may play a role in facilitating the transport of some hydrothermal Fe into the open ocean. This is important since Fe is a limiting micronutrient for primary production in large parts of the world's surface ocean. We have investigated the concentration and speciation of Fe in several vent fluid and plume samples from the Nifonea vent field, Coriolis Troughs, New Hebrides Island Arc, South Pacific Ocean using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV) with salicylaldoxime (SA) as the artificial ligand. Our results for total dissolved Fe (dFe) in the buoyant hydrothermal plume samples showed concentrations up to 3.86 µM dFe with only a small fraction between 1.1 and 11.8% being chemically labile. Iron binding ligand concentrations ([L]) were found in µM level with strong conditional stability constants up to logKFeL,Fe3+ of 22.9. Within the non-buoyant hydrothermal plume above the Nifonea vent field, up to 84.7% of the available Fe is chemically labile and [L] concentrations up to 97 nM were measured. [L] was consistently in excess of Felab, indicating that all available Fe is being complexed, which in combination with high Felab values in the non-buoyant plume, signifies that a high fraction of hydrothermal dFe is potentially being transported away from the plume into the surrounding waters, contributing to the global oceanic Fe budget.

Description: In situ effects of ocean acidification are increasingly studied at submarine CO2 vents. Here we present a preliminary investigation into the water chemistry and biology of cool temperate CO2 vents near Whakaari–White Island, New Zealand. Water samples were collected inside three vent shafts, within vents at a distance of 2 m from the shaft and at control sites. Vent samples contained both seawater pH on the total scale (pHT) and carbonate saturation states that were severely reduced, creating conditions as predicted for beyond the year 2100. Vent samples showed lower salinities, higher temperatures and greater nutrient concentrations. Sulfide levels were elevated and mercury levels were at concentrations considered toxic at all vent and control sites, but stable organic and inorganic ligands were present, as deduced from Cu speciation data, potentially mediating harmful effects on local organisms. The biological investigations focused on phytoplankton, zooplankton and macroalgae. Interestingly, we found lower abundances but higher diversity of phytoplankton and zooplankton at sites in the direct vicinity of Whakaari. Follow-up studies will need a combination of methods and approaches to attribute observations to specific drivers. The Whakaari vents represent a unique ecosystem with considerable biogeochemical complexity, which, like many other vent systems globally, require care in their use as a model of 'future oceans'.

Description: The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phases are poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopic signatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloom in subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative to particulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemical and (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surface mixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution, while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopes offer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suite of concurrent biotic and abiotic transformations of this key biolimiting element.