Consumption of dissolved oxygen in the deep Japan Sea, giving a precise isotopic fractionation factor

Concentrations and stable isotopic compositions ( δ 18 O) of dissolved O 2 in samples collected in May 2005 from the eastern Japan Sea were measured. The O 2 consumption rate and the isotopic fractionation factor ( α r ) during dissolved O 2 consumption were obtained from the field observations by applying a simple model to the deep water. The in‐situ O 2 consumption rates were calculated from the apparent O 2 utilization and the turnover time of deep water obtained in the previous tracer studies. The rates were 1.2–1.4 μ mol kg −1 yr −1 in the deep water below 2000 m. The α r estimated was 0.9875 ± 0.0003 applying a Rayleigh distillation equation to the quasi‐deep water mass of 298–3584 m. The estimated α r and the turnover time mean that δ 18 O of dissolved O 2 will increase with a rate of 0.05–0.06‰ yr −1 for the closed Japan Sea deep water mass.