Numerical Simulation of Biological Impact in Direct Injection of Carbon Dioxide in the Ocean

Direct injection of carbon dioxide (CO₂) in the deep ocean is one of the promising ways to mitigate the global warming. One of uncertainties in this method is, however, its impact on marine organisms in the near field before CO₂ is diluted widely in the ocean. Since field experiments cost enormously, computational simulations are alternatively expected to show detailed information on the dilution process near injection points and its impact on marine organisms. In general, for testing acute impact of some toxicity on organisms, the LC50 concept is widely used. As a biological impact model, we, therefore, consider mortality that reflects the recent laboratory experiment of fish and zooplankton for various concentration of CO₂. Here we regard the sigmoid-transferred mortality as a linear function of time in the logarithmic scale, not alone of the concentration of CO₂ in the logarithmic scale. This model can easily be applied to unsteady CO₂ experience for marine organisms. The model was installed in a computational simulation code for the reconstruction of small-scale ocean turbulence. Its results suggested that the effect is not nontrivial when CO₂ of 0.1ton/sec is injected in the form of spray by 100 nozzles provided vertically on a pipe with 10m interval. This is because of the initial high concentration of CO₂ near the injection points. It is, therefore, necessary to develop effective engineering measures for the initial dilution.