| Summary: | The penetration of oxygen into silty fjord sediments from northern Norway and SW Svalbard was studied at 6 sites during a research cruise to the northern Barents Sea. Profiles of oxygen were measured by microelectrodes on retrieved sediment cores in a thermostated flow aquarium and used to develop composite, 2-dimensional images of the oxygen distribution. Oxygen penetrations ranged from 3 to 11 min with a mean depth of 6 to 8 mm. The mean diffusive oxygen uptake rates across the sediment-water interface ranged from 2.8 to 13.4 mmol O-2 m(-2) d(-1). The diffusive flux accounted for 60 to 95% of the total oxygen uptake of the sediments as measured in situ by a flux chamber lander. The sediments were densely populated by fauna such as tube-dwelling polychaetes. Inhabited and relict tubes of 1 to 2.5 mm diameter reached densities of up to 1 cm(-2), and about 15 % of all oxygen microprofiles showed evidence of advective oxygen flow through the tubes. Based on oxygen microprofiles and data on burrow geometry and density, burrows extending down into the anoxic sediment extended the oxic sediment volume by 2 to 10 % and thereby enhanced the oxygen flux. Anoxic microenvironments were not detected, but during inactivity of polychaetes their tubes became depleted in oxygen relative to the surrounding sediment.
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