The direct injection of CO2 in the deep ocean is a promising way to mitigate global warming. One of the uncertainties in this method, however, is 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 expected to show detailed information on the dilution process near injection points and its impact on marine organisms. In general, the LC50 concept is widely applied for testing the acute impact of a toxic agent on organisms. As a biological impact model we therefore consider mortality, which reflects recent laboratory experiments on zooplankton at various concentrations of CO2. Here we regard the sigmoid-transformed mortality as a linear function of time in the logarithmic scale, and not just of the concentration of CO2 in the logarithmic scale. This model was installed in a computational simulation code for the reconstruction of small-scale ocean turbulence. The results suggest that the biological effect is not significant when the ship speed is 4 knots and CO2 is injected at 0.1 ton/sec in the form of a spray through 100 nozzles provided vertically on a pipe at 10 m intervals. It is therefore considered that the moving-ship method is effective for direct CO2 injection.
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