Locations:

Gulf of California
Guaymas Basin, 27 00.00 N, -111 24.00 W
Sonora Margin, 27 35.00 N, -111 28.00 W
Pescadero Basin, 24 00.00 N, -108 51.00 W

Sampling and analytical procedures:

1) Nutrients (DOC, TDN, NOx, NO2, NH4, PO4, TDP): Water sample was filtered through a pre-rinsed 0.2 um 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 (A new spectrophotometric method for the determination of nitrite in sea water. J. Mar. Res., 11: 87) as reproduced by Parsons, Marta, and Lalli, 1984.
NH4 was determined using the colorimetric method described by Solorzano, 1969.
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.

2) Alkalinity - Water sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047) into a 15 mL centrifuge tube and stored at 5°C until analysis. Alkalinity was determined using the spectrophotometric method described by Sarazin et al., 1999.

3) H2S: 5 mL water sample was collected into a 15 mL centrifuge tube containing 200 uL of 20% zinc acetate and stored at 5°C until analysis. H2S was determined using the colorimetric method described by Cline, 1969.

4) SO4: Water 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.

5) Cl - Water 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.

6) Dissolved oxygen: - DO was measured with a Thermo Orion DO probe (Prod. No. 083005MD) while sample was constantly stirred.

7) Salinity: Salinity was determined with a refractometer.

8) pH - pH was measured using a Ross electrode (Thermo Fisher, Prod. No. 8103BNUWP) calibrated with standard pH buffers of pH 4, 7, and 10.

9) CH4: - Gas samples were collected by overflowing a 1 L PETG bottle and closing headspace-free with a Teflon septum cap. A modified 1 L glass media bottle was evacuated to a pressure of 0.2 Torr or below. A 0.7 L aliquot of sample from the PETG was pulled into the evacuated bottle. The 0.7 L sample was shaken and sonicated 3x before the pressure was equilibrated by the addition of brine purged with UHP nitrogen. Extracted gases were collected from the top of the modified media bottle using a syringe and stored in 20 mL serum vials filled with brine. Methane concentrations were determined by injecting gas samples from the brine vials onto an SRI 8610 GC-FID and SRI Hayesep D 6’x1/8” column (Prod. No. 8600-PKDB). See Schmitt, 1991 and Lammers, 1994.

10) Calculated Values (NO3, DIN, DON, DOP): These values were calculated as follows:
NO3 = NOx - NO2
DIN = NOx + NH4
DON = TDN - DIN
DOP= TDP - PO4