Sequestration of C0₂ in the deep ocean by shallow injection

Abstract

To alleviate the increasing atmospheric concentrations of carbon dioxide, the principal greenhouse gas, Marchetti¹ proposed that CO₂, might be separated from flue gases and injected into the oceans. This, and subsequent studies^2–5, emphasized the need to inject the gas at great depths or in sinking currents to avoid rapid outgassing to the atmosphere. Here we show that, to the contrary, the increase in water density that results from CO₂, dissolution may be sufficient to transport the dissolved gas to lower depths even for shallow injection (in the upper 200–400 m of the ocean). If the CO₂ is injected near the shore, gravity currents will carry the dense, CO₂-rich waters along the bottom slope towards deep water. Shallow injection near the shore will be less expensive in terms of energy and capital than deep-ocean injection. We suggest that the coast of Norway, in the vicinity of existing oil and gas fields and of planned gas power plants, provides an example of a region where the negative buoyancy of CO₂-enriched sea water would transport the gas from emission sites to the deep ocean. The effect of such measures on marine life downstream of the injection point remains to be evaluated.