@ 1980, by the American Society of Limnology and Oceanography, Inc. Distribution of oxygen in marine sediments measured with microelectrodes1

Membrane-covered platinum electrodes with a tip diameter of 2-8 pm were used for an amperometric assay of dissolved oxygen in marine sediments. The oxygen profile extended to 3-5mm depth in nonilluminated sediment; even at high light intensities and at low tem-peratures it did not extend below lo-mm depth in a homogeneous sandy sediment. Oxygen profiles recorded during light-dark cycles were used to estimate the rates of oxygen produc-tion and consumption and also to calculate the apparent diffusion coefficient for oxygen in the sediment. Apparently macrofaunal activity, rather than molecular diffusion and water turbulence, was important for the occasional transport of oxygen into deeper layers and thus for the provision of oxidized conditions (positive redox potential) down to 5-10 cm below the sediment surface. Previous measurements of oxygen con-centrations in sediments are seemingly inaccurate due to the lack of a suitable analytical procedure. Brafield (1964