Health & Environmental Research Online (HERO)


Print Feedback Export to File
6109155 
Journal Article 
BIOGEOCHEMICAL CYCLING IN AN ORGANIC-RICH COASTAL MARINE BASIN .1. METHANE SEDIMENT-WATER EXCHANGE PROCESSES 
Martens, CS; Valklump, J 
1980 
Yes 
Geochimica et Cosmochimica Acta
ISSN: 0016-7037 
44 
3 
471-490 
WOS:A1980JH64700007 
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 μmol · 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 cm2 · sec−1. Dissolution of 15% of the rising bubble flux containing 86% methane supplies 170μmol · 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 μm 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.