Methanogenesis from CO₂+H₂ or acetate

Methanogenesis from H₂ and CO₂ or from acetate is measured experimentally in subcore samples
using ¹⁴C-labeled bicarbonate or acetate as tracers.

Field:

At the core processing station sub-sample mini-cores (2.2 cm diameter) are taken with clean Perspex tubes forced into the cut core surface for 10 cm. During this process a vacuum is applied by sucking a tube attached to a stopper at the top of the tube to ensure that the sediment mini-core is not compressed during sampling. The tubes have been pre-drilled with 1 mm ports at 1 cm intervals along their length and these have been sealed with a silicone based aquarium sealant.

The tubes are stoppered with a butyl rubber bung and stored temporarily, at the in situ temperature before being transported to the isotope station.

Amounts of radiotracer injected at each port are approximately;

		i)
		ii)

At the conclusion of the injections the micro-syringe is thoroughly rinsed with distilled water (10 times), to remove any residual isotope.

After injections all mini-cores are incubated at in situ temperature for 6 hours (acetate) or 18 hours (bicarbonate).

Incubations are terminated by piston extrusion of 2 cm sections of mini-core that are sliced off and put immediately into glass jars containing 7 ml of 0.5 M NaOH. The jars are tightly sealed with a butyl rubber bung, shaken to reduce the core section to a slurry, taped for security and stored upside down at room temperature to await processing.

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