Eddy correlation measurements of oxygen uptake in deep ocean sediments

We present and compare small sediment-water fluxes of O2 determined with the eddy correlation technique, with in situ chambers, and from vertical sediment microprofiles at a 1450 m deep-ocean site in Sagami Bay, Japan. The average O2 uptake for the three approaches, respectively, was 1.62 ± 0.23 (SE, n = 7), 1.65 ± 0.33 (n = 2), and 1.43 ± 0.15 (n = 25) mmol m–2 d–1. The very good agreement between the eddy correlation flux and the chamber flux serves as a new, important validation of the eddy correlation technique. It demonstrates that the eddy correlation instrumentation available today is precise and can resolve accurately even very small benthic O2 fluxes. The correlated fluctuations in vertical velocity and O2 concentration that give the eddy flux had average values of 0.074 cm s–1 and 0.049 μM. The latter represents only 0.08% of the 59 μM mean O2 concentration of the bottom water. Note that these specific fluctuations are average values, and that even smaller variations were recorded and contributed to the eddy flux. Our findings demonstrate that the eddy correlation technique is a highly attractive alternative to traditional flux methods for measuring even very small