Biogeochemical cycling in an organic-rich coastal marine basin--I. Methane sediment-water exchange processes

Details Biogeochemical cycling in an organic-rich coastal marine basin--I. Methane sediment-water exchange processes Biogeochemical cycling in an organic-rich coastal marine basin--I. Methane sediment-water exchange processes

Mar 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980gecoa..44..471m&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 44, Issue 3, pp.471-490

Physics

29

Scientific paper

Methane produced in anoxic organic-rich sediments of Cape Lookout Bight, North Carolina, enters the water column via two seasonally dependent mechanisms: diffusion and bubble ebullition. Diffusive transport measured in situ with benthic chambers averages 49 and 163 mol · m -2 · hr -1 during November-May and June-October respectively. High summer sediment methane production causes saturation concentrations and formation of bubbles near the sediment-water interface. Subsequent bubble ebullition is triggered by low-tide hydrostatic pressure release. June-October sediment-water gas fluxes at the surface average 411 ml (377 ml STP: 16.8 mmol) · m -2 per low tide. Bubbling maintains open bubble tubes which apparently enhance diffusive transport. When tubes are present, apparent sediment diffusivities are 1.2-3.1-fold higher than theoretical molecular values reaching a peak value of 5.2 × 10 -5 cm 2 · sec -1 . Dissolution of 15% of the rising bubble flux containing 86% methane supplies 170 mol · m -2 · hr -1 of methane to the bight water column during summer months; the remainder is lost to the troposphere. Bottom water methane concentration increases observed during bubbling can be predicted using a 5-15 m stagnant boundary layer dissolution model. Advective transport to surrounding waters is the major dissolved methane sink: aerobic oxidation and diffusive atmospheric evasion losses are minor within the bight.

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