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.

Caldeira, K., M.E. Wickett, and P.B. Duffy. Depth, radiocarbon and the effectiveness of direct CO2 injection as an ocean carbon sequestration strategy. Geophysical Research Letters, 10.1029/2001GL014234, 2002.

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.


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.