The oceans trap about a third of the carbon dioxide emitted into the atmosphere. They do so through two primary mechanisms: a biological ‘pump’, whereby phytoplankton absorb dissolved CO2 as they photosynthesise, and a physical ‘pump’, whereby cool, CO2-enriched water is pulled down into the depths by ocean circulation.

The data used in the present study were collected under the auspices of POMME (Multidisciplinary Meso-Scale Ocean Program), in which more than 100 researchers and engineers made four trips to the North Atlantic during 2000–01, with support from several French institutions. Using measurements of dissolved carbon from a specific location in the North Atlantic, the researchers were able to construct the first accurate carbon absorption budget for both the biological and physical pumps.

Their results suggest that in this region, absorption by the biological pump is minimal, with the physical pump capturing roughly 100 times as much carbon. The carbon is drawn down in both dissolved and inorganic forms to depths of between 200 and 400 metres, where it is effectively isolated from the atmosphere.

May 11