Two expeditions were achieved at the winter-spring transition in the Golfe de Fos (Mediterranean Sea) at a site situated at 21 m depth. An in situ autonomous oxygen profiler and laboratory oxygen mini-electrodes were used to measure the oxygen distribution in the sediments and calculate the diffusive oxygen fluxes. Clearer waters during the second expedition promoted a rapid shift from a net heterotrophic environment to a photosynthesis-dominated sediment. The diffusive exchange fluxes of oxygen through the sediment-water interface varied from an average consumption of 5.3 mmol m–2d–1 (February) to a net production of 12 mmol m–2 d–1 (March). At both periods, a large spatial heterogeneity was recorded by the different electrodes, with a larger difference between oxygen profiles when photosynthesis was active. This is probably indicative of a coupling between photosynthesis and respiration in hot spots located close to the photosynthetic organisms. The comparison between in situ micro-electrode profiles and laboratory mini-electrode measurements revealed a good agreement when respiration was dominant, but photosynthetic activity was not detected by the laboratory mini-electrode profiles.