Carbon dioxide fluxes in the global ocean

Atmospheric carbon dioxide concentration is one of the key variables of the ‘Earth system’ — the web of interactions between the atmosphere, oceans, soils and living things that determines conditions at the Earth surface. Atmospheric CO2 plays several roles in this system. For example, it is the carbon source for nearly all terrestrial green plants, and the source of carbonic acid to weather rocks. It is also an important greenhouse gas, with a central role to play in modulating the climate of the planet. During the five thousand years prior to the industrial revolution, we know (from measurements of air trapped in firn ice and ice cores) that atmospheric CO2 varied globally by less than 10 ppm from a concentration of 280 ppm (Indermuhle et al. 1999). During the late Quaternary glaciations, the regular advance and retreat of the ice was accompanied by, and to some extent at least driven by (Li et al. 1998; Shackleton 2000), an oscillation in atmospheric CO2 of about 80 ppm. Evidence from the geologically recent past indicates, therefore, that quite small changes in atmospheric carbon dioxide have big effects on planetary climate. Conversely, a stable concentration of CO2 is necessary for a stable climate. By this reasoning, we can be fairly certain that human activities will have a major effect on the climate of the planet in the near future, given that we have raised CO2 by 90 ppm in the last 150 years and it is projected to double from the pre-industrial concentration during the coming century. This gives our investigations into sources and sinks of carbon dioxide a special urgency