Distribution of oxygen in surface sediments from central Sagami Bay, Japan: In situ measurements by microelectrodes and planar optodes

Distributions of oxygen in surface sediments from central Sagami Bay were quantified using an autonomous vehicle carrying both a profiling microelectrode instrument and a planar optode module. Measurements were performed at 16 sites (either by microelectrodes or optodes) along a ∼175 m long transect and in total 45 electrode microprofiles and 6 O₂ images (each covering 6.9×5.1 cm of surface sediment) were obtained. The data revealed an extensive small-scale variation of the in situ O₂ distribution. The diffusive O₂ uptake (DOU) as derived from the microelectrode data varied by a factor >10 with an average value of 2.6±1.6 mmol m ^-2 d^-1 (n=45) corresponding to ∼8% of the estimated average primary production for the area. There was no significant difference in the average O₂ penetration depth as quantified from the microprofiles and the planar optode images (P<0.05). The O₂ penetration depth of the combined dataset varied between 0.5 and 9.2 mm with an average value of 3.9±1.5 mm (n=347). Even though the organic carbon rich sediments of central Sagami Bay may exhibit higher horizontal heterogeneity than normally encountered in deep-sea sediments, the data document that extrapolation from a few in situ data points should be done with caution. A detailed statistical analysis of the spatial autocorrelation in the O₂ penetration depth documented that measurements performed less than 2 cm apart were autocorrelated. This implies that the aerobic benthic activity at the investigated site varied in patches with a characteristic size of a few cm. The presented data represent a detailed in situ study on small-scale spatial variability in sediment O ₂ distribution and document that planar O₂ optode images provide a tool to access spatial heterogeneity of natural sediments.