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Methane production and oxidation rates

Radiotracer measurement of methane production (MP) will follow the published method of Crill and Martens (1986) and the method for methane oxidation (MO) will follow Reeburgh (1980), both as modified by Hoehler et al. (1994). For both measurements, 3 ml horizontal syringe cores of sediment will be removed at multiple depths from the large cores and stoppered without headspace using one-hole stoppers that have had the hole filled with a silicone plug. These will be amended with 25 ml of 14CH4 (gaseous, ~5x105 cpm) or NaH14CO3 (aqueous ~5x106 cpm) for MO and MP, respectively, via line injection through the silicone septa. The subcores will be incubated at the in situ temperature in the dark for suitable periods of time (1-2 days) and the samples will then be expelled into serum vials containing NaOH solution and stoppered. This will stop any further activity and preserve the sample.

The serum vials for both rate measurements will be sequentially stripped of their methane and then CO2. While the samples are in base, methane will be stripped by a stream of flowing nitrogen gas. The gas will passes through a tube furnace filled with cuprox at 800°C to combust the methane to CO2 which is then trapped in a solution of scintillation cocktail (Fisher Scintiverse II), phenethylamine and methanol. This solution will be used directly for scintillation counting of the 14C activity. The sample will then be acidified and the CO2 stripped and trapped in the same cocktail after first bubbling through a tube of 0.5 M zinc acetate solution adjusted to pH 4.0 to trap sulfide liberated by the acid.

Rates will be calculated as follows, Rate = [C]×a ×s / A×t . Here [C] is the reactant concentration (methane for MO, or CO2 for MP), a is the activity of the product, A is the activity of the reactant added, t is the incubation time, and s is the isotope fractionation factor associated with the process.


Crill, P. M. and C. S. Martens. 1986. Methane production from bicarbonate and acetate in an anoxic marine sediment. Geochim. Cosmochim. Acta 50:2089-2097.

Hoehler, T. M., M.J. Alperin, D.B. Albert and C.S. Martens. 1994. Field and laboratory studies of methane oxidation in an anoxic marine sediment: Evidence for a methanogen-sulfate reducer consortium. Global Biogeochem. Cycles 8:451-463.

Reeburgh, W. S. 1980. Anaerobic methane oxidation: Rate depth distributions in Skan Bay sediments. Earth Planet. Sci. Lett. 47:345-352.

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