Yoshio Masuda

A numerical study with an eddy-resolving model to evaluate chronic impacts in CO2 ocean sequestration

Abstract To evaluate chronic impacts of CO 2 ocean sequestration, we simulated the distribution of injected CO 2 using an oceanic general circulation model (OGCM) with a horizontal resolution of 0.1°. The model can explicitly express transport and dispersion of dissolved CO 2 by mesoscale eddies. The CO 2 which is continuously injected by a moving ship dissolves and accumulates within the first several to 10 years, but the CO 2 concentration has an upper limit after its initial increase as a result of the dilution effect of mesoscale eddies which counterbalances the accumulation effect of injection. We can estimate the CO 2 injection flux with the CO 2 maximum concentration below the “Predicted No Effect Concentration” (PNEC), an index to estimate concentration causing no effects on biota.

A lagrangian method combined with high-resolution ocean general circulation model to evaluate CO2 ocean sequestration

Publisher Summary A high-resolution model with a Lagrangian method is used to simulate the distribution and concentration of CO 2 injected into the mid-depth ocean over timescales ranging from a week to a few years. A high-resolution model with a Lagrangian tracer enables effects of eddy activities on dispersion of particles to be well represented. Comparison of Lagrangian with Eulerian tracers shows that the Lagrangian tracer avoids artificial diffusion and enables CO 2 maximum concentration at specific sites to be predicted, which helps in assessing CO 2 impact on the marine ecosystem. Ensemble experiments using high-resolution models explicitly deal with dispersion by advection due to mesoscale eddies which cannot be achieved by coarse-resolution models with implicit eddy diffusion, and enable the distribution of CO 2 maximum concentrations to be predicted. A high resolution model is demonstrated with this method is a powerful tool for assessing the effects of CO 2 injection on the marine environment.

Biological data assimilation for parameter estimation of a phytoplankton functional type model for the western North Pacific

Ecosystem models are used to understand ecosystem dynamics and ocean biogeochemical cycles and require optimum physiological parameters to best represent biological behaviours. These physiological parameters are often tuned up empirically, while ecosystem models have evolved to increase the number of physiological parameters. We developed a three-dimensional (3-D) lower-trophic-level marine ecosystem model known as the Nitrogen, Silicon and Iron regulated Marine Ecosystem Model (NSI-MEM) and employed biological data assimilation using a micro-genetic algorithm to estimate 23 physiological parameters for two phytoplankton functional types in the western North Pacific. The estimation of the parameters was based on a onedimensional simulation that referenced satellite data for constraining the physiological parameters. The 3-D NSI-MEM optimized by the data assimilation improved the timing of a modelled plankton bloom in the subarctic and subtropical regions compared to the model without data assimilation. Furthermore, the model was able to improve not only surface concentrations of phytoplankton but also their subsurface maximum concentrations. Our results showed that surface data assimilation of physiological parameters from two contrasting observatory stations benefits the representation of vertical plankton distribution in the western North Pacific.

Effect of seasonal change in gas transfer coefficient on air–sea CO 2 flux in the western North Pacific

We used an eddy-permitting three-dimensional ocean ecosystem model and applied it in the western North Pacific to understand the seasonal variations and horizontal distributions of the air–sea CO2 flux and difference in the partial pressure between sea water and the atmosphere (∆pCO2). The high-resolution model reproduced the observed zonal belt of strong CO2 uptake in the mid-latitude (30–45°N) western North Pacific including the Kuroshio extension and mixed water regions, which was difficult to show in previous coarse-resolution models. The East Asian winter monsoon, an important phenomenon in the western North Pacific, affects the seasonal CO2 air–sea gas exchange with a high (low) gas transfer coefficient in winter (summer). In the subtropical region, ∆pCO2 is negative in winter and positive in summer as a result of the temperature effect. Combination of seasonal change in gas transfer coefficient with ∆pCO2 suppresses CO2 release in the subtropical region, and vice versa in the subarctic region (i.e., suppresses CO2 uptake). That is, the East Asian winter monsoon in the western North Pacific contributes to the reduction of the annual CO2 flux through the seasonal change in the gas transfer coefficient, leading to an overall annual CO2 uptake in the subtropical region and CO2 release in the subarctic region.