We assessed diffusive oxygen uptake rates by measuring ex situ porewater oxygen microprofiles. Sediment cores were placed in a water bath and a stirring device was implemented in each core to homogenize the overlying water column and, to create a diffusive boundary layer (DBL) that was similar to in situ conditions. Microprofiles were measured using fiber-optical needle sensors (OXR50 & OXR230) constructed at Pyroscience® (Germany). After two-point calibration (0 % & 100 %) with bottom water taken from the rosette at the same station, the sensors were connected to a Firesting O2 oxygen meter (Pyroscience®) and controlled by using a computer-run micromanipulator. Vertical resolution was programmed to 100 μm, with resting time per data point of 5 seconds. Profile length was programed to be 6.5 cm.