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Supplementary Information

Organic complexation of trace metals in hydrothermal fluids, by Sander

SG, and Koschinsky A.

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 doi: 10.1038/ngeo1088

2

SI 1. Description of the geochemical modeling procedures

Geochemical speciation and reaction path modeling with the REACT sub-program of

Geochemists Workbench (GWB) Standard version 8.0 (Bethke, 2008) was used to model the

effects of organic Cu and Fe binding ligands in both hydrothermal fluid and seawater. For

this purpose, an existing thermodynamic database had to be adjusted in order to include

organic metal complexes of relevance. We modified the thermodynamic database thermo.dat

(GWB) as it includes the largest number of inorganic metal species and minerals over the

temperature range 0-300°C, while the other data bases are much too restricted with respect to

aqueous species and minerals of Cu, Fe, and other metals that are of relevance in

hydrothermal fluids. We defined two new ‘elements’, one for the organic hydrothermal

ligand (Lhy) and one for the organic seawater ligand (Lsw). The respective charged ligands

were defined as ‘basis species’ and the complexes with Cu or Fe where added to the ‘aqueous

species’.

The dissociation constants for the Cu’-Lhy and the Cu’-Lsw complex were chosen to be 10-14

as a typical value for natural complexes found in hydrothermal systems (Sander et al., 2007;

Cu’ represents some of inorganic Cu species) and seawater (e.g. Leal and van den Berg,

1998, Moffett and Dupont, 2007). Both Cu’Lsw and Cu’Lhy stability constants have been

measured by voltammetry (e.g. Sander et al., 2007; Moffett and Dupont, 2007, Leal and van

den Berg, 1998,) at room temperature after equilibration for a minimum of 8 hours. This

setup does not allow to distinguish the valence of Cu in strong organic complexes at these

concentrations, however, while Cu(I) should be the dominant redox form in reducing

hydrothermal fluids, it is Cu(II) in oxic seawater. It has been shown that Cu(I) forms strong

complexes with thiols such as glutathione (Leal and van den Berg, 1998 and Laglera and van

den Berg, 2003). Moffett and Dupont (2007) also discussed the possibility that thiol

complexes in natural seawater and specifically at depth could in fact form strong Cu(I) and

Cu(II) complexes. We therefore chose to allow hydrothermal Cu complexes of both oxidation

states.

Realistic concentrations of both Cu organic ligands were also derived from literature as being

10 nM for deep-sea water and 1 μM for the hydrothermal fluid. The latter value is

extrapolated from concentrations found in two high-temperature samples and a larger number

of low temperature hydrothermal samples published in Sander et al. (2007) and own

unpublished data. Samples with a relatively high ratio of hydrothermal fluid to seawater had



2

SI 1. Description of the geochemical modeling procedures

Geochemical speciation and reaction path modeling with the REACT sub-program of

Geochemists Workbench (GWB) Standard version 8.0 (Bethke, 2008) was used to model the

effects of organic Cu and Fe binding ligands in both hydrothermal fluid and seawater. For

this purpose, an existing thermodynamic database had to be adjusted in order to include

organic metal complexes of relevance. We modified the thermodynamic database thermo.dat

(GWB) as it includes the largest number of inorganic metal species and minerals over the

temperature range 0-300°C, while the other data bases are much too restricted with respect to

aqueous species and minerals of Cu, Fe, and other metals that are of relevance in

hydrothermal fluids. We defined two new ‘elements’, one for the organic hydrothermal

ligand (Lhy) and one for the organic seawater ligand (Lsw). The respective charged ligands

were defined as ‘basis species’ and the complexes with Cu or Fe where added to the ‘aqueous

species’.

The dissociation constants for the Cu’-Lhy and the Cu’-Lsw complex were chosen to be 10-14

as a typical value for natural complexes found in hydrothermal systems (Sander et al., 2007;

Cu’ represents some of inorganic Cu species) and seawater (e.g. Leal and van den Berg,

1998, Moffett and Dupont, 2007). Both Cu’Lsw and Cu’Lhy stability constants have been

measured by voltammetry (e.g. Sander et al., 2007; Moffett and Dupont, 2007, Leal and van

den Berg, 1998,) at room temperature after equilibration for a minimum of 8 hours. This

setup does not allow to distinguish the valence of Cu in strong organic complexes at these

concentrations, however, while Cu(I) should be the dominant redox form in reducing

hydrothermal fluids, it is Cu(II) in oxic seawater. It has been shown that Cu(I) forms strong

complexes with thiols such as glutathione (Leal and van den Berg, 1998 and Laglera and van

den Berg, 2003). Moffett and Dupont (2007) also discussed the possibility that thiol

complexes in natural seawater and specifically at depth could in fact form strong Cu(I) and

Cu(II) complexes. We therefore chose to allow hydrothermal Cu complexes of both oxidation

states.

Realistic concentrations of both Cu organic ligands were also derived from literature as being

10 nM for deep-sea water and 1 μM for the hydrothermal fluid. The latter value is

extrapolated from concentrations found in two high-temperature samples and a larger number

of low temperature hydrothermal samples published in Sander et al. (2007) and own

unpublished data. Samples with a relatively high ratio of hydrothermal fluid to seawater had

3

582 nM Lhy in 69% fluid at 294°C from Brother volcano (Sander et al., 2007) and 483 nM

Lhy in 54% fluid at 186°C from Red Lion (unpublished data cruise, M68/1, see cruise report

http://www.ifm-geomar.de/fileadmin/ifm-

geomar/fb4/fb4_fe2/spetersen/SPP_M68_1_cruise_report.pdf). Both values represent real

organic ligands after removal of acid volatile sulfides (AVS). Unfortunately, no more

measured data for organic ligand concentrations from hot and largely undiluted hydrothermal

fluids are available. In our attempts to measure Cu-binding ligand concentrations from hot

fluids of the Turtle Pits and the neighboring Red Lion vent, and from the hot vents of the

Nibelungen field (see cruise report M68/1, as above), precipitation in the voltammetric vessel

(due to the extremely high metal concentrations) prohibited a precise measurement in most

cases, and for several other samples Cu concentrations were higher than the ligand

concentrations. As the method measures the ligands in excess of the Cu concentrations,

ligand concentrations could not be determined in these samples. Only in one fluid sampled at

186°C from a chimney in the Red Lion field a ligand concentration of 483 nM (see above)

could be determined. All other successful measurements relate to more diluted or diffuse

fluids sampled at temperatures below 20°C. However, as they also reached ligand

concentrations >1 µM, similar to those found before (Sander et al., 2007), we consider a Cu-

binding hydrothermal ligand concentration of 1-10 µM a realistic range for our modeling

approach.

Ligand and complex dissociation constants for Fe were also derived from literature (Bennett

et al., 2008), with a concentration of hydrothermal ligand estimated to be 42 μM and a

seawater ligand being present at 1nM. The dissociation constants of the complexes were both

set to 10-22 (Bennett et al., 2008; Boyd et. al, 2010). We also allowed for either Fe(II) or

Fe(III) complexes with the hydrothermal ligand.

Additional to the organic ligands we modified the thermodat database by including dissolved

metal hydrosulfide species Cu(HS)+ Cu(HS)2 , Fe(HS)+, Zn(HS)+, Zn(HS)2, Mn(HS)+,

Mn(HS)2 as found by Al-Farawati and van den Berg (1999), using the same voltammetric

approach we used. These constants are comparable to the ones published by Luther et al.

(1996). Further stability constants of Cu sulfide clusters (CuS(aq) and Cu3S3(aq) ) were

included from Luther and Rickard (2005). Cu(HS) dissociation constants were from

Mountain and Seward (2003).

Despite the fact that field data and experimental evidence for the stability of organic metal

complexes at higher temperatures are largely missing, calculations of Shock and Koretsky



4

(1995), e.g., of thermodynamic properties of metal-organic complexes at high temperatures

and pressures indicate that there is a moderate temperature effect on Cu and Fe organic

complexes at temperatures above 200˚C, while at lower temperatures the stability constants

do not vary strongly. As for the inorganic speciation of the transition metals in hydrothermal

fluids, chloride and hydrosulfide complexes are the most important ones (e.g., Etschmann et

al., 2010 for Cu). Experimental investigations of their respective stabilities (e.g., Mountain

and Seward, 1999, 2003) indicate that at high temperatures Cu chloride complexes dominate,

and Cu hydrosulfide complexes will become more important at temperatures <150°C. For the

mixing of hydrothermal fluid and seawater, the extreme temperature range is only

encountered directly at the vent orifice while already much less than a meter away from the

outlet, turbulent mixing with entraining seawater reduces the temperatures significantly

below 100°C. This means that for the by far largest range of the mixing zone, for which we

consider Cu (and other metal) transport from the vent into the ocean, the reactions take place

at moderate to ambient seawater temperatures (see temperature as function of increased

mixing in SI Figure 1). Therefore, we considered the stability constants of the Cu and Fe

organic complexes in our modeling scenarios to be quasi constant. For species for which

stability constants were missing for some temperatures in the range 0-300°C in the database,

we used the extrapolate option of GWB (i.e. constants are extrapolated beyond the listed

values by polynomal fit).

For the modeling of the chemical reactions during mixing of hydrothermal fluid with

seawater the approach described in ‘Geochemical and Biogeochemical Reaction Modeling’,

chapter 22.1 by Bethke (2008) was followed. The effects of organic complexation on Cu and

Fe speciation and transport were modeled separately for Cu and Fe; however, inorganic

reactions were possible for all metals present in the database in each modeled case.

Parameters for seawater used in this work are given in Supplementary Material Table 1. CO2

(g) was swapped for H+ and O2(g) was swapped for O2(aq) for the seawater as described in

Bethke (2008) chapter 6.1. Values for the fugacities were 10-3.5 for CO2 (g) and 0.2 for O2(g).

After seawater was equilibrated at 4°C, it was ‘picked up’ as reactant and then reacted into

the hydrothermal fluid which was equilibrated at 300°C. This temperature is lower than the

endmember temperatures of the fluids (see Table 1), however, it is the maximum temperature

for which thermodynamic data are available in the database. The ‘dump option’ was switched

on, allowing minerals to be dumped from the system before starting the reaction path. This

means that when the 365 or 407°C hot fluid is equilibrated at 300°C, a significant amount of



5

minerals will precipitate and be removed from the system before the mixing with seawater

starts. We consider this to mimic the formation of smoker walls and black smoke particles

very close to the vent outlet when presumably, due to the high temperatures, organic

complexation does not yet have a strong influence. However, we have to keep in mind that,

as these precipitates are removed from the system in the initial step and are not allowed to

redissolve during further mixing, we might possibly underestimate the resulting metal fluxes

during mixing. This may be especially true for Cu, as Cu solubility is extremely temperature-

dependant, and while at temperatures >350°C large Cu concentrations are kept in solution,

cooling to 300°C already induces a significant decrease of dissolved Cu (Metz and Trefry,

2000). All but the minerals known to commonly occur in hydrothermal systems at the MAR

and that have also been observed at Turtle Pits (which are amorphous silica, anhydrite, barite,

birmessite, chalcocite, chalcopyrite, Fe(OH)2 (precipitated), Fe(OH)3 (precipitated), galena,

goethite, magnetite, nontronite (- Ca, K, Mg, Na), pyrite, pyrrhotite, sphalerite, rhombohedral

sulfur, talc and todorokite; K. Schmidt, S. Petersen, personal communication) were

suppressed.

‘Precipitation’ was switched on to allow the minerals to form and transform continuously

during mixing. Sorbed species were excluded. One kg of hydrothermal fluid was mixed in

10,000 linear steps with 1000 kg of seawater. The geochemical reaction paths were calculated

for both the Turtle Pits and the Rainbow fluids, without organic ligands, and including either

Cu-binding or Fe-binding hydrothermal ligands and/or seawater ligands. The reaction paths

were monitored and the results for mineral formation and Cu or Fe dissolved speciation and

concentrations recorded for different mixing ratios (see Supplementary Material Table 2).

Reactions were calculated using the flow-through model (Bethke, 2008) which means that

particles, once they are formed, are removed from the system and not allowed to re-dissolve

during the further modeling steps. This type of model represents a minimum approach for the

calculations of dissolved fluxes. As it is known that sulfide particles partly redissolve when

they are transported into the oxic zone during continuous mixing, the real system probably

lies between the two approaches (flow-through on and off). However, if the flow-through

option was switched off, the calculations resulted in unrealistically high dissolved metal

concentrations, due to the redissolution of sulfide minerals once the system becomes oxic.

This setting, although not entirely representing the full reality and accepting a number of

simplifications was found to be the most suitable way to demonstrate effects that have been

observed in case studies in the field, i.e. enhanced hydrothermal metal fluxes in the presence



6

of organic complexing molecules. It also allows to investigate the effects of various

parameters (such as ligand, sulfide or metal concentrations) in a more systematic way than

this is possible in the field. Once more field or experimental data are available, it is

anticipated that this modeling approach can be better constrained than it is possible at the

moment.

For our model calculations we used the pH at standard conditions instead of the in-situ pH in

our model as input parameter for the following reasons: 1). Real in-situ pH data were not

measured in the fluids, and also all other endmember fluid data had been measured under

standard conditions in the lab (see also SI Table 1). 2.) As stated in our model description we

equilibrated the endmember fluid at 300°C. After this equilibration and dumping of all

minerals precipitating during this process the pH of Turtle Pits was 4.4 (instead of 3.1 at

standard conditions). This value is close to data from Ding et al. (2005) who found that the

in-situ pH of hot hydrothermal fluids is around 5. 3) We repeated the modeling of TP with an

in-situ pH of 5 as input pH value. This resulted in a pH after equilibration (and dumping of

minerals) of 4.8. This pH difference of 0.4 units (between input pH of 3.1 or 5) resulted in a

dissolved Cu concentration in the 1:1000 hydrothermal fluid:seawater mixture of 7.7 nM for

the cases that 7.43 nM dissolved Cu had been calculated (see table Box 2, and SI Table 1). In

the case of 1 μM or 10 μM hydrothermal Cu(I)-binding ligands were present, beside 10nM

seawater ligands, the dissolved Cu concentration changed from 9.64 or 9.68 at pH 3.1 to 8.73

or 14.1 nM at pH 5, respectively. Thus although the values change slightly they are on the

same order of magnitude. We can therefore assume that the initial equilibration of data at

standard conditions at 300°C is correcting the input pH in such a way that it is close to the

predicted in-situ pH.



6

of organic complexing molecules. It also allows to investigate the effects of various

parameters (such as ligand, sulfide or metal concentrations) in a more systematic way than

this is possible in the field. Once more field or experimental data are available, it is

anticipated that this modeling approach can be better constrained than it is possible at the

moment.

For our model calculations we used the pH at standard conditions instead of the in-situ pH in

our model as input parameter for the following reasons: 1). Real in-situ pH data were not

measured in the fluids, and also all other endmember fluid data had been measured under

standard conditions in the lab (see also SI Table 1). 2.) As stated in our model description we

equilibrated the endmember fluid at 300°C. After this equilibration and dumping of all

minerals precipitating during this process the pH of Turtle Pits was 4.4 (instead of 3.1 at

standard conditions). This value is close to data from Ding et al. (2005) who found that the

in-situ pH of hot hydrothermal fluids is around 5. 3) We repeated the modeling of TP with an

in-situ pH of 5 as input pH value. This resulted in a pH after equilibration (and dumping of

minerals) of 4.8. This pH difference of 0.4 units (between input pH of 3.1 or 5) resulted in a

dissolved Cu concentration in the 1:1000 hydrothermal fluid:seawater mixture of 7.7 nM for

the cases that 7.43 nM dissolved Cu had been calculated (see table Box 2, and SI Table 1). In

the case of 1 μM or 10 μM hydrothermal Cu(I)-binding ligands were present, beside 10nM

seawater ligands, the dissolved Cu concentration changed from 9.64 or 9.68 at pH 3.1 to 8.73

or 14.1 nM at pH 5, respectively. Thus although the values change slightly they are on the

same order of magnitude. We can therefore assume that the initial equilibration of data at

standard conditions at 300°C is correcting the input pH in such a way that it is close to the

predicted in-situ pH.

7

SI Table 1: Composition of seawater and hydrothermal fluid endmembers, as used for

the modeling.

Parameter unit Seawater Turtle Pits Rainbow T ˚C 4 407* 365* pH** (25°C) 8.1 3.1 2.8 CH4 mM/kg 0 0.045 2.5 H2 mM/kg 0 0.66 16 H2S mM/kg 0 4.2 1.0 SO4 mM/kg 28.2 0 0 Ba µM/kg 0.2 5.4 67 Ca mM/kg 10.3 8.8 67 Cl mM/kg 546 271 750 Cu µM/kg 0.007 76 140 Fe µM/kg 0.0007 3,940 24,000 K mM/kg 10.1 8.6 20 Mg mM/kg 54.5 0 0 Mn µM/kg 0.001 473 2,250 Na mM/kg 488 237 553 Si mM/kg 0.17 11.6 6.9 Sr µM/kg 90 254 200 Zn µM/kg 0.01 69 160 *modeled at 300°C **input pH represents pH measured at standard conditions Seawater data: Bethke et al. (2008), chapter 22.2 Black smokers Turtle Pits data: Koschinsky et al. (2008) and Haase et al. (2007) for CH4 and H2 Rainbow data: Douville et al. (2002) and Charlou et al. (2002) for CH4 and H2



8

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.

a) Rainbow Mixing factor

Pyrite (moles)

Sphalerite (moles)

Chalcocite (moles)

Goethite (moles)

Todorokite (moles)

Birnessite (moles)

diss. Cu (moles/kg)

no Lhy no Lsw

0.4 3.33E-05 1 3.35E-04 2.33E-05

10 4.34E-03 1.09E-04 3.84E-05 2.97E-03 1.14E-08 100 4.34E-03 1.09E-04 3.84E-05 1.73E-02 7.38E-06 8.60E-08 7.50E-09

1000 4.34E-03 1.09E-04 3.84E-05 1.73E-02 7.38E-06 1.96E-07 7.05E-09 1µM Cu(I)Lhy 10nM Cu(II)Lsw

0.4 3.33E-05 1 3.35E-04 2.33E-05

10 4.34E-03 1.09E-04 3.81E-05 2.87E-03 6.30E-08 100 4.34E-03 1.09E-04 3.81E-05 1.73E-02 7.38E-06 8.59E-08 1.33E-08


0.4 3.33E-05 1 3.35E-04 2.34E-05

10 4.34E-03 1.09E-04 3.59E-05 5.30E-07 100 4.34E-03 1.09E-04 7.38E-06 3.59E-05 8.71E-08 6.48E-08

1000 4.34E-03 1.09E-04 7.38E-06 3.59E-05 1.97E-07 1.26E-02 1.29E-08



9

a) Turtle Pits Mixing factor

Pyrite (moles)

Sphalerite (moles)

Chalcocite (moles)

Goethite (moles)

Todorokite (moles)

Birnessite (moles)

diss. Cu (moles/kg)

no Lhy no Lsw

0.2 2.11E-05 1 1.98E-04 1.33E-05

10 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 2.90E-06 4.57E-08 100 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 2.92E-06 1.12E-08

1000 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 3.03E-06 7.43E-09 no Lhy 10nM Cu(II)Lsw

0.2 2.11E-05 1 1.98E-04 1.33E-05

10 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 2.90E-06 4.57E-08 100 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 2.92E-06 1.13E-08


0.2 2.11E-05 1 1.98E-04 1.33E-05

10 2.36E-03 6.05E-05 3.47E-05 1.64E-03 6.74E-05 1.65E-07 2.24E-07 100 2.36E-03 6.05E-05 3.47E-05 1.64E-03 6.74E-05 1.78E-07 3.30E-08

1000 2.36E-03 6.05E-05 3.47E-05 1.64E-03 6.74E-05 2.87E-07 9.64E-09 1µM Cu(II)Lhy 10nM Cu(II)Lsw

0.2 2.11E-05 1 1.98E-04 1.33E-05

10 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 2.90E-06 4.98E-08 100 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 2.92E-06 1.13E-08

1000 2.36E-03 6.04E-05 4.04E-05 1.58E-03 6.43E-05 3.03E-06 7.43E-09 Lhy = hydrothermal ligand, Lsw = seawater ligand, Cu(I)L = Cu(I)-binding ligand, Cu(II)L = Cu(II)-binding ligand Mineral formations and dissolved Fe concentrations were calculated correspondingly by including organic seawater and hydrothermal ligands for Fe.



10

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.



11

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.



12

SI: References: Al-Farawati, R. & van den Berg, C.M.G., Metal-sulfide complexation in seawater. Mar.

Chem. 63, 331-352 (1999). Bennett, S.A. et al., The distribution and stabilisation of dissolved Fe in deep-sea

hydrothermal plumes. Earth Planet. Sci. Lett. 270, 157-167 (2008). Bethke, C., Geochemical and biogeochemical reaction modeling. Cambridge University

Press, New York. 522 pp. (2008). Bewers, J.M. & Yeats, P.A., Oceanic residence times of trace metals. Nature 268, 595-598

(1977). Boyd, P.W., Ibisanmi, E., Sander, S.G., Hunter, K.A., & Jackson, G.A., Remineralization of

upper ocean particles: Implications for iron biogeochemistry. Limnol. Oceanogr. 55, 1271-1288 (2010).

Bruland, K.W., Orians, K.J., Cowen, J.P., Reactive trace-metals in the stratified central North Pacific. Geochim. Cosmochim. Acta 58, 3171–3182 (1994).

Charlou, J.L., Donval, J.P., Fouquet, Y., Jean-Baptiste, P., & Holm, N., Geochemistry of high H2 and CH4 vent fluids issuing from ultramafic rocks at the Rainbow hydrothermal field (36°14'N, MAR). Chem. Geol. 191, 345-359 (2002).

Ding, K., Seyfried, W. E. J., Zhang, Z., Tivey, M. K., Von Damm, K. L., and Bradley, A.M.. The in-situ pH of hydrothermal fluids at mid-ocean ridges. Earth and Planetary Science Letters 237, 167-174 (2005).

Douville, E. et al., The Rainbow vent fluids (36°14'N, MAR): The influence of ultramafic rocks and phase separation on trace metal content in Mid-Atlantic Ridge hydrothermal fluids. Chem. Geol. 184, 37-48 (2002).

Elderfield, H. & Schulz, H., Mid-Ocean Ridge Hydrothermal Fluxes and the Chemical Composition of the Ocean. Annu. Rev. Earth Planet. Sci. 24, 191-224 (1996).

Etschmann, B.E. et al., An in situ XAS study of copper(I) transpsort as hydrosulfide complexes in hydrothermal solutions (25-592˚C, 180-600 bar): Speciation and solubility in vaor and liquid phases. Geochim. Cosmochim. Acta 74, 4723-4739 (2010).

Haase, K.M. et al., Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge. G3, Geochem. Geophys. Geosyst. 8, 10.1029/2006GC001509 (2007).

Koschinsky, A. et al., Hydrothermal venting at pressure-temperature conditions above the critical point of seawater, 5 degrees S on the Mid-Atlantic Ridge. Geology 36 , 615-618 (2008).

Laglera, L.M. & van den Berg, C.M.G., Copper complexation by thiol compounds in estuarine waters. Mar. Chem. 82, 71-89 (2003).

Leal, M.F.C. & van den Berg, C.M.G., Evidence for Strong Copper(I) Complexation by Organic Ligands in Seawater. Aquat. Geochem. 4, 49-75 (1998).

Luther III, G.W. & Rickard, D.T., Metal sulfide cluster complexes and their biochemical importance in the environment. J. Nanoparticle Res. 7, 389-407 (2005).

Luther III, G.W., Rickard, D.T., Theberge, S., & Olroyd, A., Determination of metal (bi)sulfide stability constants of Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ by voltammetric methods. Environ. Sci Technol. 30, 671-679 (1996).

Metz, S & Trefry, J.H., Chemical and mineralogical influences on concentrations of trace metals in hydrothermal fluids. Geochim. Cosmochim. Acta 64, 2267-2279 (2000).

Moffett, J.W. & Dupont, C., Cu complexation by organic ligands in the sub-arctic NW Pacific and Bering Sea. Deep-Sea Res. I 54, 586-595 (2007).



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Mountain, B.W. & Seward, T.E., Hydrosulfide/sulfide complexes of copper(I): Experimental confirmation of the stoichiometry and stability of Cu(HS)2

- to elevated temperatures. Geochim. Cosmochim. Acta 67, 3005-3014 (2003).

Mountain, B.W. & Seward, T.E., The hydrosulfide/sulfide complexes of copper(I): Experimental determination of stochiometry and stability at 22˚C and reassessment of high temperature data. Geochim. Cosmochim. Acta 63, 11-29 (1999).

Nielsen, S.G. et al., Hydrothermal fluid fluxes calculated from the isotopic mass balance of thallium in the ocean crust. Earth Planet. Sci. Lett. 251, 120-133 (2006).

Sander, S.G., Koschinsky, A., Massoth, G.J., Stott, M., & Hunter, K.A., Organic complexation of copper in deep-sea hydrothermal vent systems. Environm. Chem. 4, 81-89 (2007).

Shock, E.L. and Korentsky, C.M., Metal-organic complexes in geochemical processes: Estimation of standard partial molal thermodynamic properties of aqueous complexes between metal cations and monovalent organic acid ligands at high pressures and temperatures. Geochim. Cosmochim. Acta 95, 1497-1532 (1995).

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