Auxiliary Material for Paper 2011GB004156 Model design, input parameters, and additional information for a quantitative geochemical model along a transect off Peru 1. Regional setting 1.1 Shelf sites 680, 681 and Site 679 The shelf sites 680 and 681 are located in the Salaverry Basin (Figure S1.1). Sediments recovered from the shelf sites conform with basically upwelling-related deposits. They contain total organic carbon-rich (TOC-rich) diatomaceous ooze and mud accumulated throughout the Pleistocene and Holocene periods. Older sediments from the Miocene and Pliocene ages have lower TOC content, contain more clastic components, and are coarser grained (Emeis and Morse, 1990). TOC content in the upper 150 mbsf varies between 1 and 10 wt. % (cf. Figure 2a of the main text; Suess et al., 1988). The mixing of seawater-derived pore water and a hypersaline, subsurface brine have caused strong positive chloride and sodium concentration gradients in the pore water profiles from Sites 680 and 681 (Figure S3.2 and Kastner et al., 1990). Sulphate, calcium, and magnesium concentration profiles are also characterised by brine reflux. Site 679 is located at the seaward edge of the outer shelf at a water depth of 450 m. A structural ridge separates this site from the sub-surface brine. Thus, this site is geochemically characterised by seawater chloride concentrations as high as 200 mbsf. Below, in the section from the middle Miocene period, chloride concentrations decrease to 62 % of seawater chloride (Kastner et al., 1990). Suess et al. (1988) proposed dilution with middle to late Miocene period fresh water while the ridge was subaerially exposed, restricting the Salaverry Basin. Quaternary and late Pliocene sediments from Site 679 consist of TOC-rich, alternately laminated and bioturbated diatomaceous mud. Units from the middle Miocene to early Pliocene periods contain coarser-grained sediments of terrigenous origin, as is also the case at Sites 680 and 681. Sediments contain sparse diatoms and low-angle, cross-bedded silts and fine-grained sands. This indicates exposure of the Salaverry basin area to high-energy bottom currents prior to at least 4-5 Ma. At this time, Sites 679, 680, and 681 were probably located inshore of the centres of present day upwelling in a shallow water environment (Suess and von Huene, 1988). 1 Figure S1.1. Map indicating the study sites. ODP Leg 112, Sites 679, 680, 681, 682, and ODP Leg 201, Site 1231 (modified after Shipboard Scientific Party, 1988). 1.2 Lower slope sites 682 and 688 Site 688 is located at a water depth of 3,820 m in the secondary depositional centre of the lower slope (Figure S1.1) with material derived from resuspension on the shelf and upper slope. TOCrich diatomaceous ooze and mud accumulated throughout the Quaternary period. The TOC content in Quaternary and Pliocene sediments is between 2 and 10 wt.%. Sediments from the Miocene and early Pliocene ages consist of laminated, organic carbon-rich mud with TOC contents up to 4 wt.% (cf. Figure 2a of the main text; Suess et al., 1988). The deposition of these upwelling sediments at the lower slope is consistent with the inferred seaward shift of the upwelling zone during this time and with the subsidence history of the Lima basin. Sediments from Sites 682 and 688 at the lower slope have been subject toprogressive subsidence since the Eocene period and were located underneath a coastal upwelling cell throughout the upper Miocene period (Suess and von Huene, 1988; von Huene and Suess, 1988). At Site 682 sediments from the Pleistocene to middle Eocene periods were recovered. Sediments at Site 688 reflect progressively deeper water sedimentation from early Eocene to Pleistocene times (Kvenvolden and Kastner, 1990). Gas hydrates were recovered at Site 688. On the other hand, geophysical data from Site 682 yielded strong evidence that gas hydrates were present but direct observations are lacking 2 (Kvenvolden and Kastner, 1990). Bottom-simulating reflectors (BSRs) were detected at both sites (Suess et al., 1988). In much of the sediment column of Site 688 gas hydrates are probably present, between depths of about 20 m and the bottom of the gas hydrate stability zone at about 500 mbsf (Kvenvolden and Kastner, 1990). 1.3 Open ocean site 1231 Site 1231 is located within the Peru Basin at a water depth of 4,827 m. Sediments from the Holocene to late Eocene ages were recovered. The sequence mostly consists of diatom-rich clay with TOC contents between 0.1 and 0.7 wt.% (cf. Figure 5a of the main text; Suess et al., 1988). Iron- and manganese-rich nannofossile ooze occurs in the late Eocene to early Oligocene sediments (Shipboard Scientific Party, 1976; Shipboard Scientific Party, 2003b). Iron and manganese concentrations in the pore waters are about one order of magnitude higher in the upper 45 metres of the sediments than in the lower section. Also pore water sulphate concentrations are higher in the upper part of the section. Concentration profiles of the other dissolved species lack evidence of post-depositional reactions (Brady and Gieskes, 1976; Shipboard Scientific Party, 2003a). 2. Explanation of the PHREEQC (version 2) model The latest version of PHREEQC can be downloaded from the USGS website: http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/. The user’s guide (Parkhurst & Appelo, 1999), containing a description of data input, can be downloaded from the same website. The effect of varying total pressure on aqueous species distribution and associated solid phases is minor (Table S2.1). Calculations are of the calcite solubility in pure water at 7°C and pressures of 1 atm (calculated with PHREEQC and wateq4f.dat dataset) and 92 atm (log KCalcite is calculated with SUPCRIT92 and DPRONS92.dat dataset; Johnson et al., 1992). Table S2.1. Effect of the different pressure of 1 atm (calculated with PHREEQC and wateq4f.dat dataset) and 92 atm (calculated with SUPCRT92 and DPRONS92.dat dataset, Johnson et al., 1992) on an equilibrium constant of Calcite (log KCc), calcium-equilibrium concentration [mmolkgw-1) and pH [-]. FeCO3 = Fe2+ + CO32-. p = 1.0 atm p = 92 atm 3 T [°C] log KCc [-] 7 -8.40 Ca-equilibrium concentration [mmol kgw-1] 0.1329 pH [-] log KCc [-] 9.934 -8.30 Ca-equilibrium concentration [mmol kgw-1] 0.1471 pH [-] 9.965 4 The clay mineral content of the sediments (Tables S2.2–S2.7) (Clayton and Kemp, 1990) also enables estimation of its cation exchange capacity (Jasmund and Lagaly, 1993). Calculations assume a sediment mass of 1.89 kg per cell and meq = mmol gives 1.2 mol of exchangers (expressing the cation exchange capacity in PHREEQC) in each cell of the PHREEQC model. The initial occupancy of exchange sites is defined by equilibration with seawater prior to diagenetic processes. Table S2.2. PHREEQC model setup and input parameters of Site 679. RV: representative volume, SI: saturation index, CEC: cation exchange capacity. model setup parameters number of RVs height RV Vtot RV Vaq RV time per shift a total time modelled b total sediment depth b diffusion boundary conditions database 50 10 m 1.7 L 1.0 L 357,143 yrs 17,857,150 yrs 495 m constant (top) closed (bottom) wateq4f.datc physical parameters bottom water temperature d geothermal gradient d sedimentation rate d pressure (constant) 12.5°C 20°C km–1 2.8 cm kyr–1 70.05 atm geochemical parameters starting solutions primary phases f SiO2(amorph) Illite Chlorite14A Kaolinite Goethite Calcite Pyrolusite secondary phases Calcite Dolomite Siderite Ca-Rhodochrosite Greigite CFA Sepiolite(d) gas phases CEC g transport diffusion coefficient h sea water e mol/RV (SI) x y z 10 / 10 / 10 (0) 0.82 / 0.35 / 0.26 (0) 0.10 / 0.09 / 0.03 (0) 0.13 /0.15 / 0.07 (0) 0.41 / 0.41 / 0.41 (0) 0.60 / 0.60 / 0.60 (0) 0.05 / 0.05 / 0.05 (0) mol/RV (SI) 0 (0) 0 (1.3) 0 (0.3) 0 (0.85) 0 (0) 0 (0) 0 (0) CO2(g), CH4(g), N2(g) 1.2 mol/RV diffusion 0.86E–09 m2s–1 a : calculated from sedimentation rate and height of RVs : calculated from sedimentation rate, number and height of RVs c : Parkhurst and Appelo (1999) d : from Suess et al. (1988) e : after Nordstrom et al. (1979) f : according to Suess et al. (1988) and Clayton and Kemp (1990) g : cation exchange capacity, depends on the clay mineral content, estimated according to Jasmund and Lagaly (1993) h : mean value for all dissolved species, calculated according to diffusion coefficients given in Giambalvo et al. (2002) x : cells 50 to 46 y : cells 45 to 27 b 5 z : cells 26 to 1 Table S2.3. PHREEQC model setup and input parameters of Site 680. RV: representative volume, SI: saturation index, CEC: cation exchange capacity. model setup parameters geochemical parameters number of RVs 50 starting solutions height RV Vtot RV Vaq RV time per shift a total time modelled b total sediment depth b diffusion boundary conditions 10 m 1.7 L 1.0 L 384,615 yrs 19,230,750 yrs 495 m constant (top) constant (bottom) wateq4f.datc primary phases g SiO2(amorph) Illite Chlorite14A Kaolinite Goethite sea water e subsurface brinef mol/RV (SI) 10y / 10z (0) 0.70 / 0.14 (0) 0.11 / 0.04 (0) 0.11 /0.02 (0) 0.41 / 0.41 (0) secondary phases Calcite Dolomite Siderite Greigite CFA mol/RV 0 0 0 0 0 gas phases CEC h transport diffusion coefficient i CO2(g), CH4(g), N2(g) 1.2 mol/RV diffusion 0.86E–09 m2s–1 database physical parameters bottom water temperature d geothermal gradient d sedimentation rate d pressure (constant) 13°C 54°C km–1 2.6 cm kyr–1 50.25 atm (SI) (0) (1.3) (0.3) (0) (0) a : calculated from sedimentation rate and height of RVs : calculated from sedimentation rate, number and height of RVs c : Parkhurst and Appelo (1999) d : from Suess et al. (1988) e : after Nordstrom et al. (1979) f : after Kastner et al. (1990) g : according to Suess et al. (1988) and Clayton and Kemp (1990) h : cation exchange capacity, depends on the clay mineral content, estimated according to Jasmund and Lagaly (1993) i : mean value for all dissolved species, calculated according to diffusion coefficients given in Giambalvo et al. (2002) y : cells 50 to 45 z : cells 44 to 1 b 6 Table S2.4. PHREEQC model setup and input parameters of Site 681. RV: representative volume, SI: saturation index, CEC: cation exchange capacity. model setup parameters geochemical parameters number of RVs 50 starting solutions height RV Vtot RV Vaq RV time per shift a total time modelled b total sediment depth b diffusion boundary conditions 10 m 1.7 L 1.0 L 125,000 yrs 6,250,000 yrs 495 m constant (top) constant (bottom) wateq4f.datc primary phases g SiO2(amorph) Illite Chlorite14A Kaolinite Goethite sea water e subsurface brinef mol/RV (SI) 10z (0) 0.33 (0) 0.07 (0) 0.07 (0) 0.41 (0) secondary phases Calcite Dolomite Siderite Greigite CFA mol/RV 0 0 0 0 0 gas phases CEC h transport diffusion coefficient i CO2(g), CH4(g), N2(g) 1.2 mol/RV diffusion 0.86E–09 m2s–1 database physical parameters bottom water temperature d geothermal gradient d sedimentation rate d pressure (constant) 13.5°C 32.5°C km–1 8 cm kyr–1 40.05 atm (SI) (0) (1.3) (0.85) (0) (0) a : calculated from sedimentation rate and height of RVs : calculated from sedimentation rate, number and height of RVs c : Parkhurst and Appelo (1999) d : from Suess et al. (1988) e : after Nordstrom et al. (1979) f : after Kastner et al. (1990) g : according to Suess et al. (1988) and Clayton and Kemp (1990) h : cation exchange capacity, depends on the clay mineral content, estimated according to Jasmund and Lagaly (1993) i : mean value for all dissolved species, calculated according to diffusion coefficients given in Giambalvo et al. (2002) z : cells 50 to 1 b 7 Table S2.5. PHREEQC model setup and input parameters of Site 682. RV: representative volume, SI: saturation index, CEC: cation exchange capacity. model setup parameters number of RVs height RV Vtot RV Vaq RV time per shift a total time modelled b total sediment depth b diffusion boundary conditions database 50 10 m 1.7 L 1.0 L 571,429 yrs 28,571,450 yrs 495 m constant (top) closed (bottom) wateq4f.datc physical parameters bottom water temperature d geothermal gradient d sedimentation rate d pressure (constant) 1.5°C 42.5°C km–1 1.75 cm kyr–1 403.85 atm geochemical parameters starting solutions primary phases f SiO2(amorph) Illite Chlorite14A Kaolinite Goethite Calcite Pyrolusite secondary phases Calcite Dolomite Siderite Ca-Rhodochrosite Greigite CFA CH4Hydrate gas phases CEC g transport diffusion coefficient h sea water e mol/RV (SI) 10w / 10x / 10y / 10z (0) 1.02 / 0.51 / 0.14 / 0.11 (0) 0.12 / 0.07 / 0.02 /0.003 (0) 0.16 /0.15 / 0.05 / 0.01 (0) 0.68 / 0.68 / 0.68 / 0.68 (0) 0.75 / 0.75 / 0.75 / 0.75 (0) 0.01 / 0.01 / 0.01 / 0.01 (0) mol/RV (SI) 0 (0) 0 (1.3) 0 (0.3) 0 (0.85) 0 (0) 0 (0) 0 (0) CO2(g), CH4(g), N2(g) 1.2 mol/RV diffusion 0.86E–09 m2s–1 a : calculated from sedimentation rate and height of RVs : calculated from sedimentation rate, number and height of RVs c : Parkhurst and Appelo (1999) d : from Suess et al. (1988) e : after Nordstrom et al. (1979) f : according to Suess et al. (1988) and Clayton and Kemp (1990) g : cation exchange capacity, depends on the clay mineral content, estimated according to Jasmund and Lagaly (1993) h : mean value for all dissolved species, calculated according to diffusion coefficients given in Giambalvo et al. (2002) w : cells 50 to 40 x : cells 39 to 20 y : cells 19 to 11 z : cells 10 to 1 b 8 Table S2.6. PHREEQC model setup and input parameters of Site 688. RV: representative volume, SI: saturation index, CEC: cation exchange capacity. model setup parameters number of RVs height RV Vtot RV Vaq RV time per shift a total time modelled b total sediment depth b diffusion boundary conditions database 50 10 m 1.7 L 1.0 L 33,333 yrs 1,666,650 yrs 495 m constant (top) closed (bottom) wateq4f.datc physical parameters bottom water temperature d geothermal gradient d sedimentation rate d 1.8°C 47°C km–1 30 cm kyr–1 pressure (constant) 406.98 atm geochemical parameters starting solutions primary phases f SiO2(amorph) Illite Chlorite14A Kaolinite Goethite Calcite Pyrolusite secondary phases Calcite Siderite Ca-Rhodochrosite Greigite CFA FCO3Apatite Struvite CH4Hydrate gas phases CEC g transport diffusion coefficient h sea water e mol/RV (SI) 10x / 10y / 10z (0) 0.47 / 0.87 / 0.28 (0) 0.07 / 0.13 / 0.05 (0) 0.11 /0.19 / 0.11 (0) 0.68 / 0.68 / 0.68 (0) 0.60 / 0.60 / 0.60 (0) 0.00 / 0.75 / 0.00 (0) mol/RV (SI) 0 (0) 0 (0.3) 0 (0.85) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) CO2(g), CH4(g), N2(g) 1.2 mol/RV diffusion 0.86E–09 m2s–1 a : calculated from sedimentation rate and height of RVs : calculated from sedimentation rate, number and height of RVs c : Parkhurst and Appelo (1999) d : from Suess et al. (1988) e : after Nordstrom et al. (1979) f : according to Suess et al. (1988) g : cation exchange capacity, depends on the clay mineral content, estimated according to Jasmund and Lagaly (1993) h : mean value for all dissolved species, calculated according to diffusion coefficients given in Giambalvo et al. (2002) x : cells 50 to 38 y : cells 37 to 18 z : cells 17 to 1 b 9 Table S2.7. PHREEQC model setup and input parameters of Site 1231. RV: representative volume, SI: saturation index, CEC: cation exchange capacity. model setup parameters number of RVs height RV Vtot RV Vaq RV time per shift a total time modelled b total sediment depth diffusion boundary conditions database 50 10 m 1.7 L 1.0 L 666,667 yrs 33,333,350 yrs 495 m constant (top) closed (bottom) wateq4f.datc physical parameters bottom water temperature d geothermal gradient d sedimentation rate d pressure (constant) 1.9°C 62.5°C km–1 1.5 cm kyr–1 407.7 atm geochemical parameters starting solutions primary phases f SiO2(amorph) Illite Chlorite14A Kaolinite Goethite Pyrolusite sea water e mol/RV 10x / 10y / 10z 0.58 / 0.73 / 0.44 0.11 / 0.14 / 0.09 0.11 /0.13 / 0.08 0.68 / 0.68 / 0.68 0.02 / 0.02 / 0.02 secondary phases Calcite Dolomite Siderite Ca-Rhodochrosite Greigite CFA CH4Hydrate gas phases CEC g transport diffusion coefficient h mol/RV (SI) 0 (0) 0 (1.3) 0 (0.3) 0 (0.85) 0 (0) 0 (0) 0 (0) CO2(g), CH4(g), N2(g) 1.2 mol/RV diffusion 0.86E–09 m2s–1 (SI) (0) (0) (0) (0) (0) (0) a : calculated from sedimentation rate and height of RVs : calculated from sedimentation rate, number and height of RVs c : Parkhurst and Appelo (1999) d : from Shipboard Scientific Party (2003b); Shipboard Scientific Party (1976) e : after Nordstrom et al. (1979) f : according to Suess et al. (1988) and Clayton and Kemp (1990) g : cation exchange capacity, depends on the clay mineral content, estimated according to Jasmund and Lagaly (1993) h : mean value for all dissolved species, calculated according to diffusion coefficients given in Giambalvo et al. (2002) x : cells 50 to 48 y : cells 47 to 46 z : cells 45 to 1 b 10 Table S2.8. Equilibrium phases, mass-action equations and equilibrium constants (log K, at 25°C and 1bar pressure). Equilibrium constants are from the “wateq4f.dat” data set (Parkhurst and Appelo, 1999). Equilibrium Phase Equilibrium Reaction log K –2.71 18.66 SiO2(a) Sepiolite(d) SiO2 + 2H2O = H4SiO4 Mg2Si3O7.5OH:3H2O + 0.5H2O + 4H+ = 2Mg+2 + 3H4SiO4 Illite K0.6Mg0.25Al2.3Si3.5O10(OH)2 + 11.2H2O = 0.6K+ + 0.25Mg+2 + 2.3Al(OH)4– + 3.5H4SiO4 + 1.2H+ –40.267 Al2Si2O5(OH)4 + 6H+ = 2Al+3 + 2H4SiO4 + H2O Mg5Al2Si3O10(OH)8 + 16H+ = 5Mg+2 + 2Al+3 + 3H4SiO4 + 6H2O FeOOH + 3H+ = Fe+3 + 2H2O MnO2 + 4H+ + 2e– = Mn+2 + 2H2O CaCO3 = Ca+2 + CO3–2 FeCO3 = Fe+2 + CO3–2 CaMg(CO3)2 = Ca+2 + Mg+2 + 2CO3–2 7.435 68.38 –1.0 41.38 –8.48 –10.75 –17.09 Mn0.9Ca0.1CO3 = 0.1Ca+2 + 0.9 Mn+2 +CO3–2 –10.39a Kaolinite Chlorite14A Goethite Pyrolusite Calcite Siderite Dolomite CaRhodochrosite Greigite Fe3S4 + 4H+ = 2Fe+3 + Fe+2 + 4HS– –45.035 Ca9.316Na0.37Mg0.144(PO4)5.63(CO3)1.2 = 9.316Ca+2 + 0.37Na+ + 0.144Mg+2 CFA –114.4b + 5.63PO4–3 + 1.2CO3–2 Ca9.316Na0.36Mg0.144(PO4)4.8(CO3)1.2F2.48 = 9.316Ca+2 + 0.36Na+ + FCO3Apatite –114.4 0.144Mg+2 + 4.8PO4–3 + 1.2CO3–2 + 2.48F– Struvite MgNH4PO4:6H2O = Mg+2 + NH4+ + PO4–3 + 6H2O –13.26c CH4Hydrate CH4:6H2O = CH4 + 6H2O –1.073d CO2(g) CO2 = CO2 –1.468 CH4(g) CH4 = CH4 –2.860 N2(g) N2 = N2 –3.260 a : obtained from Rhodochrosite. b : obtained from FCO3Apatite. c : defined after Ronteltap et al.(2007). d : calculated from Gibb’s free energy (ΔG = 5.736 kJ molī1), pressure (P = 10MPa), and temperature (T = 279.55 K) after Lu et al. (2008). 11 3. Model results and measured data Figure S3.1. A) Modelled and measured inorganic carbon (IC) content (wt. %) of the shelf and lower slope sites.B) Modelled dissolved CO2 concentration (mM) profiles of the shelf and lower slope sites. C) Modelled and measured pH (-) profiles of the shelf and lower slope sites. Grey dots: modelled data, diamonds: measured data. Measured TOC contents and pore water concentration data are taken from Suess et al. (1988). Red numbering indicates sedimentary units according to Suess et al. (1988). 12 Figure S3.2. A) Modelled and measured chlorinity (mM) profiles of the shelf and lower slope sites. B) Modelled and measured calcium concentration (mM) profiles of the shelf and lower slope sites. C) Modelled and measured magnesium concentration (mM) profiles of the shelf and 13 lower slope sites. D) Modelled and measured iron concentration (mM) profiles of the shelf and lower slope sites. Grey dots: modelled data, diamonds: measured data. Measured pore water concentration data are taken from Suess et al. (1988) and the Shipboard Scientific Party (2003a). Red numbering indicates sedimentary units according to Suess et al. (1988). Figure S3.3. Modelled and measured inorganic carbon (IC) content (wt. %) and modelled and measured concentration (mM) and pH (-) profiles of the open ocean site 1231. Grey dots: modelled data, diamonds: measured data. Measured pore water concentration data are taken from the Shipboard Scientific Party (2003b). Red numbering indicates sedimentary units according to the Shipboard Scientific Party (2003b). 14 References Arning, E.T., Y. Fu, W. van Berk and H.-M. Schulz (2011) Organic carbon remineralization and complex, early diagenetic solid – aqueous solution – gas interactions: Case study ODP Leg 204, Site 1246 (Hydrate Ridge), Mar. Chem., 126, 120–131, doi:10.1016/j.marchem.2011.04.006. Brady, S., and J. M. 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