INTERNATIONAL JOURNAL OF ENERGY, ENVIRONMENT, ECONOMICS, Vol. 1, No. 2, pp. 119-127,1991

Oceanic Sinks for Anthropogenic CO₂

C. L. Sabine and F. T. Mackenzie

Prior to human activities, there was a net flux of CO₂ from the ocean through the atmosphere to the land. This flux fueled organic production in terrestrial ecosystems. Human interference in the CO₂ cycle has reversed the role of the ocean as a CO₂ source; it is now a net sink of anthropogenic CO₂. The strength of this sink is debatable. Sinks include solution of CO₂ in surface seawater, and the more minor processes of dissolution of carbonates, nutrient fertilization and increased organic carbon burial, increased fluxes of stream-derived particulate organic carbon (POC) and dissolved organic carbon (DOC) to the oceans, and increased dissolved inorganic carbon (DIC) flux from increased weathering. We determine that the sink strength of the combined minor fluxes is roughly 760 MTCY(-1). Dissolution of benthically-derived carbonate skeletons may account for about 7% of this flux. The process and importance of dissolution are discussed in light of sediment trap and water carbon chemistry data from the Hawaiian Archipelago. Each minor sink taken individually may not seem important when viewed against the atmospheric CO₂ increase of 3000 MTCY(-1). However, collectively these minor sinks amount to about 25% of the atmospheric sink. We determined that most of the minor sinks will not increase significantly in the future; however, a reassessment of the sink owing to dissolution of carbonate particles both on shelf-bank areas and in the water column suggests that the fluxes associated with this sink may become greatly enhanced in the future, if society continues its present practices.