Long-term and Real-time Monitoring of CO₂ and O₂ Fluxes in Tokyo Bay: A Basis for Coastal Environment-Ecosystem Models Applicable to Climate Change

Abstract

Nutrients that enter Tokyo Bay become a source of primary production, absorbing CO₂ from the atmosphere and releasing O₂. These processes were investigated. Data from continuous measurements of water quality, flow velocity, and meteorology were used. With changing weather, the fluxes of O₂ and CO₂ frequently switched between absorption and release in opposite phases to each other. The O₂:CO₂ ratio due to biological metabolism was about 1:1, whereas the O₂:CO₂ ratio of sea surface fluxes was about 10:1, with annual averages of 65.4 for O₂ emission and 7.4 for CO₂ absorption in mmol m^-2 d^-1. The equilibration time for O₂ was short, and O₂ generated by primary production was quickly released to the atmosphere. On the other hand, the equilibration time for CO₂ was much longer than the residence time of the bay water, and the amount of CO₂ absorbed within the bay appeared to be about 1/10 of the CO₂ absorption capacity produced by nutrient influx. O₂ flux measurements are important in bays with short residence times. Vertical circulation flow in the bay was also measured and a conceptual diagram of primary production and O₂ and CO₂ transport for the entire bay was presented.