THE DEEP OCEAN DISPOSAL OF CARBON-DIOXIDE

Once released to the environment, carbon dioxide equilibrates within the ocean-atmosphere pool. Because the mixing of surface seawater is relatively slow, release to the atmosphere causes a transient peak in atmospheric carbon dioxide concentration. If the release could be transferred to the ocean, this transient might be avoided. In addition, interaction with the large carbon pool contained within the ocean sediment would be accelerated. The resultant increase in ocean alkalinity would tend to reduce equilibrium P(CO2) values. The dynamics of the processes involved are complex and not yet understood in detail. This paper reviews deep ocean carbonate chemistry and mixing, and estimates their relative importance for the prediction of atmospheric carbon dioxide concentrations resulting from deep ocean release. Predictions based on mathematical modelling suggest that disposal into the surface ocean (< 1 km depth) would permit equilibration with the atmosphere within a few years to decades and would therefore offer little advantage. Disposal into ocean basins greater than 3km in depth would delay equilibration with the atmosphere for several hundred years, eliminating the atmospheric concentration transient. Resultant interaction with calcite-rich sediments could probably reduce the long-term (> 2000 year) atmospheric enrichment by a significant amount (approximately 50%)