Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate/Ocean acidification and ocean carbon cycle
Depth, radiocarbon and the effectiveness of direct CO2 injection as an ocean carbon sequestration strategy
Ken Caldeira, Michael E. Wickett & Philip B. Duffy
The use of deep sea injection has often been proposed as a way to reduce the effects of carbon emissions. However, the effectiveness of such a method must be determined before it is implemented. In this paper, the effectiveness of depth and radiocarbon as efficiency predictors are compared.
Sequestration efficiency at various depths: The eventual effiency of carbon sequestration is shown for three different depths. The large change in efficiency between each depth implies that depth has a great impact on sequestration effiency and could be used as a predictor for how well it would work.
Sequestration efficiency as a function of depth and radiocarbon levels: When plotted against both depth and radiocarbon levels, sequestration efficiency works as a function of depth but not of radiocarbon levels. Hence, depth will work better as a predictor in the future.
Abstract
If radiocarbon were a good predictor of the amount of time until a water parcel returns to the surface, it could be used to estimate the effectiveness of carbon sequestration by direct injection. We performed direct CO2 injection simulations in both one-dimensional box-diffusion and three-dimensional ocean general circulation models. The 1-D model results for ocean carbon retention accord with the 3-D model results, especially in the Pacific basin and at shallower depths. In the 1-D model, carbon retention in the ocean is directly related to both the injection depth and the _14C of carbon at the injection location. However, in the 3-D model, depth, but not radiocarbon, provides a relatively good prediction of carbon retention. This suggests that the expected time for a water parcel to return to the surface is closely related to its depth and not in general to the time since last at the surface.