Geochem. Geophys. Geosys. 9, Q02012 (2008)

Credit: SAMSUL ADAM

Engineered storage of carbon dioxide deep in the ocean has been suggested as a way of mitigating climate change, but some anthropogenic carbon dioxide has already begun to make its way to the ocean floor naturally. A new study finds that as carbon dioxide-rich surface water continues to sink over the coming centuries, the ocean floor will become an increasingly acidic and hostile habitat.

Marion Gehlen at the Laboratoire des Sciences du Climat et de l'Environnement, France, and colleagues used a combined global biogeochemical and sediment model to simulate the changes in deep-sea chemistry that would occur with an increase in atmospheric carbon dioxide of one percent per year over the next 140 years. They found that the acidity of deep-sea water would rise steadily, with the most pronounced changes occurring in areas of deep-water formation, such as the North Atlantic.

Such changes could alter the composition of deep-sea communities. From tiny plankton to giant clams, many marine animals make their shells of calcium carbonate, which dissolves in acidic waters. The area of deep-sea floor favourable to these organisms could decrease by 58 percent, warn the researchers, who also predict a six percent decline in shell material preserved in the upper deep-sea sediment.