Dataset: Geochemical measurements of porewater and sediment from push core samples collected in the Gulf of California during R/V Atlantis cruise AT50-22 in 2024

Sediment samples were collected by the HOV Alvin 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) 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) NH4: 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, preserved with phenol reagent and stored at 5°C until analysis using the colorimetric method described by Solorzano, 1969. Samples were analyzed on a Hach DR 3900 spectrophotometer.

3) 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. Samples were analyzed on a Hach DR 3900 spectrophotometer.

4) H2S: 2.0 mL unfiltered water sample was collected into a 15 mL centrifuge tube containing 500 uL of 20% zinc acetate and stored at 5°C until analysis.  H2S was determined using the colorimetric method described by Cline, 1969.  Samples were analyzed on a Hach DR 3900 spectrophotometer.

5) VFA: 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 and stored frozen at -20°C until analysis. VFA (Glycolate, Lactate, Acetate, Formate, iso-Butyric Acid, Butyric Acid, iso-Valeric Acid, Valeric Acid) analysis was performed on a Dionex UltiMate 3000 HPLC with Hamilton PRP-1 Guard Column (Prod. No. 79445), Brownlee NewGuard RP-8 7 µm 15 x 3.2 mm guard column (Prod. No. 0711-0090) and Brownlee SPHERI-5 RP-8 5 µm 250 x 4.6 mm analytical column (Prod. No. 4427064) following the method of Albert and Martens, 1997.

6) 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 with a Dionex Integrion HPIC using KOH eluent supplied by a Dionex EGC 500 KOH Eluent Generator Cartridge (Prod. No. 075778), Dionex CR-ATC Continuously Regenerated Trap Column (Prod. No. 088662), Dionex ADRS 600 Dynamically Regenerated Suppressor (Prod. No. 088666), Dionex IonPac AG18 Guard Column (Prod. No. 060551), Dionex IonPac AS18 Analytical Column (Prod. No. 060549) and Dionex CRD 200 Carbonate Removal Device (Prod. No. 062983). See Weston et al., 2006.

7) 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 with a Dionex Integrion HPIC using KOH eluent supplied by a Dionex EGC 500 KOH Eluent Generator Cartridge (Prod. No. 075778), Dionex CR-ATC Continuously Regenerated Trap Column (Prod. No. 088662), Dionex ADRS 600 Dynamically Regenerated Suppressor (Prod. No. 088666), Dionex IonPac AG18 Guard Column (Prod. No. 060551), Dionex IonPac AS18 Analytical Column (Prod. No. 060549) and Dionex CRD 200 Carbonate Removal Device (Prod. No. 062983).  See Weston et al., 2006.

8) Na: 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 with a Dionex Integrion HPIC using Methanesulfonic Acid eluent supplied by a Dionex EGC 500 MSA Eluent Generator Cartridge (Prod. No. 076779), Dionex CR-CTC Continuously Regenerated Trap Column (Prod. No. 088663), Dionex CDRS 600 Dynamically Regenerated Suppressor (Prod. No. 088670CMD), Dionex IonPac CG12A Guard Column (Prod. No. 046076), Dionex IonPac CS12A Analytical Column (Prod. No. 046075).

9) K: 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 with a Dionex Integrion HPIC using Methanesulfonic Acid eluent supplied by a Dionex EGC 500 MSA Eluent Generator Cartridge (Prod. No. 076779), Dionex CR-CTC Continuously Regenerated Trap Column (Prod. No. 088663), Dionex CDRS 600 Dynamically Regenerated Suppressor (Prod. No. 088670CMD), Dionex IonPac CG12A Guard Column (Prod. No. 046076), Dionex IonPac CS12A Analytical Column (Prod. No. 046075).

10) Mg: 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 with a Dionex Integrion HPIC using Methanesulfonic Acid eluent supplied by a Dionex EGC 500 MSA Eluent Generator Cartridge (Prod. No. 076779), Dionex CR-CTC Continuously Regenerated Trap Column (Prod. No. 088663), Dionex CDRS 600 Dynamically Regenerated Suppressor (Prod. No. 088670CMD), Dionex IonPac CG12A Guard Column (Prod. No. 046076), Dionex IonPac CS12A Analytical Column (Prod. No. 046075).

11) Ca: 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 with a Dionex Integrion HPIC using Methanesulfonic Acid eluent supplied by a Dionex EGC 500 MSA Eluent Generator Cartridge (Prod. No. 076779), Dionex CR-CTC Continuously Regenerated Trap Column (Prod. No. 088663), Dionex CDRS 600 Dynamically Regenerated Suppressor (Prod. No. 088670CMD), Dionex IonPac CG12A Guard Column (Prod. No. 046076), Dionex IonPac CS12A Analytical Column (Prod. No. 046075).

12) Fe(II): 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 analyzed following a modified version of Stookey, 1970.  Samples were analyzed on Hach DR 3900 and Shimadzu UV-1601 spectrophotometers.

13) pH: Sediment pH was determined using an Oakton pH5S pH spear (Prod. No. 3563452) and measured immediately during core sectioning.

14) Eh: Sediment Eh was measured using a Mettler Toledo InLab Redox ORP Electrode (Prod. No. 51343203) and a Fisherbrand Accumet AP125 Portable Meter (Prod. No. 13-636-AP125A).

15) Salinity: Porewater salinity was determined using a Fisherbrand handheld refractometer (Prod. No. 12-561-335).

16) DIC: Water sample was filtered through a pre-rinsed 0.2 μm regenerated cellulose Target2 syringe filter (Thermo Scientific, Prod. No. F25047). A 2.0 mL sample was injected into a N2-purged serum vial crimp-sealed with a butyl rubber stopper.  Samples were stored frozen at -20°C until analysis. Sample analysis was performed after thawing and acidifying samples with concentrated HCl to pH 0.  DIC concentration was determined by injecting headspace samples onto a Shimadzu GC-2014 FID-Methanizer with Supelco Carboxen 1010 PLOT 30 m x 0.53 mm Fused Silica Capillary Column (Prod. No. 25467).  Weston et al. 2006

17) Gases: Methane, Ethane, Propane, iso-Butane, n-Butane and n-Pentane samples (3 cc whole sediment) were collected into a glass serum vial, preserved with 2 mL 2M N2-purged NaOH, crimp-sealed with a butyl rubber stopper and stored at room temperature until analysis.  Concentrations were determined by headspace analysis using an SRI 8610 GC-FID with Agilent J&W HP-PLOT Al2O3 S Capillary Column, 50 m, 0.53 mm, 15.00 μm (Prod. No. 19095P-S25E). See Joye et al., 2004.

18) SOM:  Sediment samples collected and analyzed for porosity were subsequently analyzed for Sediment Organic Matter.  SOM was determined by drying a sample of known mass at 80C, weighing, ashing at 500C, weighing and calculating weight loss on ignition.

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

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

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

22) Calculated Values (NO3, DIN, DON, DOP, PIC):  These values were calculated as follows:

• NO3 = NOx - NO2
• DIN = NOx + NH4
• DON = TDN - DIN
• DOP = TDP - PO4
• PIC = TPC - POC