Deep penetrating benthic oxygen profiles measured in situ by oxygen optodes

For the first time in situ, deep penetrating O-2 profiles were measured in abyssal sediments in the western South Atlantic, Construction of deep penet rating O-2 optodes and adaptation to a benthic profiling lander are describ ed. The opto-chemical oxygen sensors allow measurements to a depth of 55 cm in marine sediments, A vertical resolution of 0.5 cm was used to determine the O-2 dynamics in those oligotrophic deep sea sediments; the oxygen conc entration across the sediment water interface was measured with a resolutio n of 100 mum. Oxygen penetration depth (OPD), diffusive oxygen uptake (DOU) and oxygen consumption rates were determined at four stations north of the Amazon fan and one at the Mid-Atlantic Ridge, Diffusive oxygen uptake rate s ranged from 0.1 to 0.9 mmol m-(2) d(-1); the oxygen penetration depth ran ged from 8 to 26 cm, Carbon consumption rates calculated from the diffusive oxygen uptake rates were in the range of 0.3-3.0 g C m(-2) a(-1). Comparis on between in situ and laboratory DOU and OPD measurements confirmed previo us findings that core recovery and warming have strong effects on the oxyge n dynamics in deep sea sediments. Laboratory measurements yielded a decreas e of 50-75% in OPD and consequently an increase in DOU by 1.5 and 18-times. Deep penetrating oxygen optodes provide a new tool to accurately determine oxygen dynamics (and thereby calculate carbon mineralization rates) in oli gotrophic sediments. However, oxygen optodes as used in this study do not r esolve the diffusive boundary layer (DBL). The data show that deep penetrat ing O-2 optodes in combination with high-resolution O-2 microelectrodes giv e a complete picture of the oxygen dynamics, including the DBL, in deep sea sediments. (C) 2001 Elsevier Science Ltd. All rights reserved.