Dataset: Methane Isotopes
Deployment: NH1319

Sediment cores were recovered using the following coring equipment:
Ocean Instruments multicorer MC-800 (SP1215) and MC-400 (NH1319)
OSU Gravity Core (6 meters long, 4 inch diameter)
OSU “Big Bertha” Core (12 meters long, 4 inch diameter)

Multi cores were immediately transferred into a refrigerated van. They were then extruded in an N2 atmosphere within 2-12 hours of recovery.

Gravity cores were sectioned on deck immediately upon recovery. All but one of the gravity cores were secured horizontally on the ship’s deck and sampled from the bottom of the core upwards by sequentially removing 10 cm sediment intervals by cutting the core liner using a pipe cutter. One core was secured vertically and sampled similarly, but from the top down. Freshly exposed sediment was immediately subsampled using 3- to 60-mL push corers made of plastic syringes with the tips removed. All subcores, except those for methane (see next paragraph), were immediately transferred to a N2 filled glove bag in the refrigerated van for further processing.

All sediment aliquots were centrifuged in polycarbonate tubes at 4 degrees C. The supernatant was collected into all-polypropylene syringes with stainless steel needles, and filtered through disposable 0.2 um nylon filters with 0.7 um GF/F pre-filter (Whatman 6870-2502). The first 3 mL were discarded. To minimize the DOC blank, 100 mL of UV-irradiated deionized water were pushed through each disposable filter prior to use. DIC samples for 13C and 14C abundances were immediately flame-sealed under a stream of ultra-high-purity (UHP) N2 into 10-15 mL borosilicate tubes spiked with HgCl2 following (McCorkle et al., 1985). DOC samples for concentration determination only were acidified and ampoulated under a stream of UHP N2 gas and refrigerated. DOC samples for isotopic analyses were frozen without acidification in 20 mL scintillation vials with Teflon-lined caps. Samples for methane concentration and delta 13C values were immediately placed into 20-mL serum glass vials (Wheaton) containing a 5-mm glass bead, basified, sealed with a blue butyl rubber septum (Chemglass), homogenized, crimp sealed, and stored upside down at room temperature until analysis. For analysis of delta 14C values of methane, 150- and 250-mL sediment aliquots were immediately placed into 250- and 500-mL glass media bottles (VWR) containing 80 and 100 mL of 1 M KOH solution, respectively. The bottles were immediately capped with #7 rubber stoppers, sealed thoroughly with electric tape, screw capped, and stored upside down at room temperature until analysis. Centrifuge tubes containing sediment were frozen.

All tools and parts were first cleaned with household dish soap, then acid rinsed (exclusive of metal parts). Plasticware was air dried; glassware and metal tools were baked at 550 degrees C for 4 hours. Bottom-water DIC and DOC samples were collected with a Go Flo bottle following DOE (1994) and Beaupré et al. (2007), respectively.

For further details including quality assurance measures for DOC, see Komada et al. (2013) and Komada et al. (2016). Also refer to the table of information on the methods, relative uncertainity, and references for each analyte (PDF).

References:
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Komada T., Burdige D. J., Crispo S. M., Druffel E. R. M., Griffin S., Johnson L. and Le D. (2013) Dissolved organic carbon dynamics in anaerobic sediments of the Santa Monica Basin. Geochim. Cosmochim. Acta 110, 253–273.

Komada T., Burdige D. J., Li H. L., Magen C., Chanton J. P. and Cada A. K. (2016) Organic matter cycling across the sulfate-methane transition zone of the Santa Barbara Basin, California Borderland. Geochim. Cosmochim. Acta 176, 259–278.

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