BENTHIC OXYGEN FLUXES ON THE WASHINGTON SHELF AND SLOPE - A COMPARISON OF INSITU MICROELECTRODE AND CHAMBER FLUX MEASUREMENTS

Benthic oxygen fluxes calculated from in situ microelectrode profiles are compared with benthic flux chamber O2 uptake measurements on a transect of eight stations across the continental shelf and three stations on the slope of Washington State. Station depths ranged from 40 to 630 m and bottom-water oxygen concentrations were 127-38-mu-M. The fluxes measured by the two methods were similar on the slope, but on the shelf, the chamber flux exceeded the microelectrode flux by as much as a factor of 3-4. We attribute this difference to pore-water irrigation, a process which apparently accounts for the oxidation of a significant amount of organic C in the continental shelf sediments. Combining our diffusive flux data with other data demonstrates clearly that the bottom-water oxygen concentration must play some significant role in determining the sedimentary oxygen consumption rate. Numerical simulation of the microelectrode O2 profiles suggests that roughly half the diffusive O2 flux must be consumed within approximately 1 mm of the sediment surface. If this conclusion is correct, then the magnitude of the diffusive flux depends both on the bottom-water oxygen concentration and on the supply rate of labile C to the sediment surface.