DIFFUSION-COEFFICIENTS OF SULFATE AND METHANE IN MARINE-SEDIMENTS - INFLUENCE OF POROSITY

Tracer diffusion coefficients of sulfate and methane were determined in seawater (D(o)) and in sediments (D(s)). The diffusion coefficients in seawater (20 parts per thousand S) at 4-degrees-C were 0.56 +/- 0.04*10(-5) cm2 s-1 for sulfate and 0.87 +/- 0.10*10(-5) cm2 s-1 for methane. The sediment diffusion coefficients can be related to the diffusion coefficient in free solution by D(s) = D(o)/theta2, where theta is the tortuosity of the sediment. The sediment tortuosity calculated from this equation showed a linear relationship with sediment porosity (phi) over the porosity range of 0.4-0.9. From our data, it was possible to deduce the empirical equation theta2 = 1 + n(1 - phi), which was used to calculate D(s) from D(o):D(s) = D(o)/1 + n(1 - phi), using n = 3 for clay-silt sediments and n = 2 for sandy sediments.