SUPPLEMENTARY INFORMATION DOI: 10.1038/NGEO1088 NATURE GEOSCIENCE | www.nature.com/naturegeoscience 1 Index: page SI 1 Description of the geochemical modeling procedures 2 SI Table 1 Composition of seawater and hydrothermal fluid 7 endmembers, as used for the modeling SI Table 2 Results of modeling the Cu fluxes during mixing of hydrothermal 8 endmember a) Rainbow, and 8 b) Turtle Pits with seawater 9 SI Figure 1 Graphic presentation of excerpts of the modeling results, 10 showing changes of temperature, redox potential, pH, dissolved Cu concentrations, and mineral formation during mixing of 1 kg hydrothermal fluid (Turtle Pits) with up to 1000 kg of seawater. SI 2 Calculation of Cu and Fe fluxes from hydrothermal sources 11 SI References 12 Metal flux from hydrothermal vents increased by organic complexation
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Supplementary Information SUPPLEMENTARY INFORMATION · Geochemical speciation and reaction path modeling with the REACT sub-program of Geochemists Workbench (GWB) Standard version
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SI Table 2: Results of modeling the Cu fluxes during mixing of hydrothermal endmember a) Rainbow, and b) Turtle Pits with seawater. Model settings: precipitation on (allowing minerals to form), extrapolate thermodynamic data, step width of mixing 0.0001, dump minerals (removes minerals formed in the initial equilibrium step from the system). All calculations were made in the flow-through mode, which prevents minerals to re-dissolve once they precipitate, simulating fallout of particles from the plume. The flow-through model may lead to an underestimate of dissolved metal fluxes, thus representing a minimum scenario. The table lists a selection of minerals and their quantities formed at specific mixing ratios, and the resulting dissolved Cu concentrations at these mixing ratios.
SI Figure 1: Graphic presentation of excerpts of the modeling results, showing changes of temperature, redox potential, pH, dissolved Cu concentrations, and mineral formation during mixing of 1 kg hydrothermal fluid (Turtle Pits) with up to 1000 kg of seawater.
SI 2. Calculation of Cu and Fe fluxes from hydrothermal sources Hydrothermal fluxes of dissolved Cu and Fe into the deep ocean were calculated under the following assumptions: The global hydrothermal water flux is 7.2x 1012 kg/year (Nielsen et al., 2006). Assuming Cu hydrothermal endmember concentrations of 9.7 x 10-6 moles/kg as the minimum value (Elderfield and Schulz, 1996) and the Rainbow vent fluid as the maximum value (140 x 10-6 moles/kg) we calculated an annual hydrothermal Cu flux between 6.98 x 107 kg/year and 10 x 107 kg/year for the two extreme values. These values are multiplied by the % of dissolved hydrothermal Cu entering the deep ocean with respect to the endmember concentration (Box 2 table, values in parentheses). These values range between 0.04 and 0.56% when no organic ligands are present and between 0.45 and 4.12% when organic ligands where present. This results in values for dissolved Cu between 2.09 and 13.3 x 106 moles/year entering the deep ocean and originating from hydrothermal vents. Assuming now a deep-ocean volume of 2.6 x 1020 L and a dissolved Cu concentration of 0.7 x 10-9 moles/kg we can calculate the total amount of dissolved Cu in the deep ocean (1.82 x 1012 moles). Taking a residence time of Cu in the ocean of 6,400 years (Bewers and Yeats, 1977), we receive an annual Cu flux required to maintain the dissolved Cu concentration in the deep-ocean of 2.84 x 108 moles/year. Using now the values for dissolved Cu in kg/year entering the deep ocean and originating from hydrothermal vents we calculated a percentage of dissolved Cu in the deep ocean to originate for hydrothermal vents as being between 0.74% (assuming all minimum values) and 14.2% assuming values valid for the Rainbow hydrothermal vent field in case Cu(I) binding organic ligands are present in hydrothermal vent systems. In the absence of organic complexation (including those in seawater) only 0.14 % of dissolved Cu may originate from hydrothermal vents. Similar calculations were done for Fe assuming a minimum Fe concentration in hydrothermal endmembers of 0.75 x 10-3 mol/kg (Elderfield and Schulz, 1996) and a maximum of 24 x 10-3
mol/kg Fe as found in the Rainbow endmember (Douville et al., 2008). A residence time of 70 to 140 years (Bruland et al., 1994) and a deep-ocean dissolved Fe concentration of 0.7 x 10-9 mol/kg were assumed. As a result we calculated in the presence of 42 x 10-6 mol/kg Lhy values between 0.69 to 9.3% of all dissolved Fe in the deep ocean to be from hydrothermal sources. In the absence of hydrothermal ligands, but the presence of Fe-binding ligands in seawater (Lsw) a maximum of 0.01% of all dissolved Fe in the deep ocean to be from hydrothermal sources. In the absence of any organic ligand (i.e., no Lhy and Lsw) dissolved Fe is not stable in seawater.
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