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 similar to 175m long transect and in total 45 electrode microprofiles and 6 O-2 images (each covering 6.9 x 5.1 cm of surface sediment) were obtained. The data revealed an extensive small-scale variation of the in situ O-2 distribution. The diffusive O-2 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 similar to 8% of the estimated average primary production for the area. There was no significant difference in the average O-2 penetration depth as quantified from the microprofiles and the planar optode images (P <0.05). The O-2 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 O-2 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 O-2 optode images provide a tool to access spatial heterogeneity of natural sediments. (c) 2005 Elsevier Ltd. All rights reserved.