A new in situ instrument for two-dimensional mapping of oxygen in coastal s
ediments is presented. The measuring principle is described, and potential
mechanical disturbances, solute and particle smearing associated with the m
easurements, and calibration routines are evaluated. The first in situ meas
urements obtained in two different benthic communities are presented. In a
shallow photosynthetic sediment (1 m of water depth), an extensive horizont
al and temporal variation in the O-2 distribution caused by benthic photosy
nthesis and irrigating fauna was resolved. Repetitive planar optode measure
ments performed along a transect in central Oresund, Denmark (17 in of wate
r depth) revealed a positive correlation between the apparent O-2 penetrati
on depths (OP) measured with a lateral distance <5.0 mm, whereas OP measure
d with a larger horizontal distance (up to 50 m) were not correlated. Conse
quently, the OP varied in patches with a characteristic size of 5.0 min. Th
e instrument described is a powerful new tool for in situ characterization
of spatiotemporal variations in O-2 distributions within benthic communitie
s. The instrument can be adapted for use at full ocean depths, e.g., on dee
p-sea landers or remote operating vehicles.