Location:
Guaymas Basin, Gulf of California, 27 00.00 N, -111 20.00 W

Sampling and analytical procedures:

Sediment samples were collected by the ROV SuBastian using PVC push cores. Upon arrival at the surface the cores were described and cataloged prior to being sectioned into discrete depth intervals. Porewater was separated from the sediment using a manually-actuated porewater press as described by Joye et al. 2004. Following the collection of porewater, the pressed sediment sample (mud-cake) was stored at -20°C for solid-phase analysis. Porewater and sediment samples were preserved and analyzed as follows:

1) pH: Sediment pH was determined using a sediment probe (Oakton, Prod. No. 35634-50) and measured immediately during core sectioning. Porewater pH was determined using a Ross electrode (Thermo Fisher, Prod. No. 8103BNUWP).

2) Salinity: Porewater salinity was determined using a handheld refractometer.

3) Nutrients (DOC, TDN, NOx, NO2, PO4, TDP): Porewater sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047), collected into an HDPE bottle and stored frozen at -20°C until analysis. Individual analytes were analyzed as follows:
DOC was determined using high temperature catalytic combustion and an NDIR detector following the method described in Sugimura and Suzuki, 1988.
TDN was determined using high temperature combustion and a chemiluminescence detector following the method described in Watanabe et. al, 2007.
NOx was determined using chemical reduction and a nitric oxide detector following the method described by Garside, 1982.
NO2 was determined using the colorimetric method described by Bendschneider and Robinson, 1952 as reproduced by Parsons, Marta, and Lalli, 1984.
PO4 was determined using the colorimetric method described by Strickland and Parsons, 1972.
TDP was determined using the colorimetric method described by Solorzano and Sharp, 1980.

4) NH4: Porewater sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047), collected into a 15 mL centrifuge tube containing 100 μL of phenol reagent (cold; 4°C) per 1 mL of sample, and stored at 4°C until analysis. NH4 was determined using the colorimetric method described by Solorzano, 1969.

5) Alkalinity: Porewater sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047). Alkalinity was determined using the spectrophotometric method described by Sarazin et al., 1999.

6) Methane, Ethane, and Propane: Sediment samples (3 cubic centimeters) were collected into a glass serum vial, preserved with N2-purged 2M NaOH (3 milliliters), crimp-sealed with a butyl rubber stopper and stored at room temperature until analysis. Concentrations were determined by headspace analysis using an SRI 8610C gas chromatograph equipped with a flame ionization detector and SRI Hayesep D 6’x1/8” column (Prod. No. 8600-PKDB).

7) H2S: 2 mL porewater sample was collected into a 15 mL centrifuge tube containing 100 uL or 500 uL 20% zinc acetate w/v solution and stored at 5°C until analysis. H2S was determined using the colorimetric method described by Cline, 1969.

8) Sulfate (SO4): Porewater sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047) into a 7 mL scintillation vial. Samples were acidified with 10 μL of concentrated HNO3 per 1 mL sample, sealed with a PTFE lined cap, and stored at room temperature until analysis. Sample analysis was performed using KOH eluent supplied by a Dionex EGC III KOH Eluent Generator Cartridge (Prod. No. 074532), Dionex CR-ATC Continuously Regenerated Trap Column (Prod. No. 060477), Dionex AERS 500 Electronically Regenerated Suppressor (Prod. No. 082541), Dionex IonPac AG19 Guard Column (Prod. No. 062888), Dionex IonPac AS19 Analytical Column (Prod. No. 062886) and Dionex CRD 200 RFIC Carbonate Removal Device (Prod. No. 062986). Reference - Weston et al. 2006, Biogeochemistry 77: 375-408.

9) Chloride (Cl): Porewater sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047) into a 7 mL scintillation vial. Samples were acidified with 10 μL of concentrated HNO3 per 1 mL sample, sealed with a PTFE lined cap, and stored at room temperature until analysis. Sample analysis was performed using KOH eluent supplied by a Dionex EGC III KOH Eluent Generator Cartridge (Prod. No. 074532), Dionex CR-ATC Continuously Regenerated Trap Column (Prod. No. 060477), Dionex AERS 500 Electronically Regenerated Suppressor (Prod. No. 082541), Dionex IonPac AG19 Guard Column (Prod. No. 062888), Dionex IonPac AS19 Analytical Column (Prod. No. 062886) and Dionex CRD 200 RFIC Carbonate Removal Device (Prod. No. 062986). Reference - Weston et al. 2006, Biogeochemistry 77: 375-408.

10) Porosity: Sediment samples were collected into glass scintillation vials, capped and stored at 4°C until analysis. Porosity was determined by drying a sample of known mass at 80°C, weighing, and calculating the moisture content.

11) SOM (LOI): Sediment samples were collected into glass scintillation vials, capped and stored at 4°C until analysis. SOM was determined by drying a sample at 80°C, weighing, ashing at 500°C, weighing and calculating weight lost on ignition.

12) TPN: The pressed sediment sample (mud-cake) was dried at 60°C and then homogenized via grinding. TPN was determined by the method described by Gordan, Jr., 1969 as reproduced by Sharp, 1974. Samples were analyzed on a ThermoFinnigan FlashEA 1112 series NC Soil Analyzer.

13) TPC: The pressed sediment sample (mud-cake) was dried at 60°C and then homogenized via grinding. TPC was determined by the method described by Gordan, Jr., 1969 as reproduced by Sharp, 1974. Samples were analyzed on a ThermoFinnigan FlashEA 1112 series NC Soil Analyzer.

14) POC: The pressed sediment sample (mud-cake) was acidified with 1 N HCl, dried at 60°C, and then homogenized via grinding. POC was determined by the method described by Gordan, Jr., 1969 as reproduced by Sharp, 1974. Samples were analyzed on a ThermoFinnigan FlashEA 1112 series NC Soil Analyzer.

15) TPP and TPP percent: The pressed sediment sample (mud-cake) was dried at 80°C, ground, and distributed into 20 mL scintillation vials. The samples were prepared using the method described by Zhou et. al., 2003. TPP and TPP percent were determined using the colormetric method described by Solorzano and Sharp, 1980.

16) Calculated Values: Values for NO3, DIN, DON, DOP, PIC were calculated as follows:
NO3 = NOx - NO2
DIN = NOx + NH4
DON = TDN - DIN
DOP = TDP - PO4
PIC = TPC - POC

Known Issues:

PW NO2: The following samples were cloudy and most had no visible pink color development. Concentrations given are estimates made by visually comparing sample tubes to standards. Samples: 2, 3, 6-8, 11-14, 16-19, 39-41, 43-51, 65, 66, 68, 69, 72-76

PW PO4: The following samples were cloudy but had blue color development. Concentrations given are estimates made by visually comparing sample tubes to standards. Samples: 3, 6-8, 11-14, 18, 19, 41, 45-47, 49, 65, 66, 68, 69, 72-74, 76, 77