A specialist in the study of the changes in the planetary carbon cycle over ice age and inter ice age time scales, Guy Munhoven, a researcher at the ULg’s Laboratory of Planetary and Atmospheric Physics (LPAP), has developed a model of the oceanic carbon cycle which he has leashed together with a model of sea bed sediments.

Since the debut of the industrial era, at the start of the eighteenth century, carbon dioxide (CO₂) emissions have literally exploded, leading the average concentration in the atmosphere to grow from around 280 ppm (parts per million) to 384 ppm (in 2007), which is a rise of over 30%. In other words the expansion of human activity has to a very large degree contributed to a growth in CO₂ concentrations without precedent over the course of the last 800,000 years. Each year human activities effectively release into the atmosphere some 8 billion tons of carbon in the form of carbon dioxide (the figures for 2005), of which only half accumulates in the atmosphere, the rest being absorbed by the oceans or the terrestrial biosphere. One of the principal consequences of this evolution is very clearly global warming – a worrying subject for the scientific community and which political decision makers are starting to become aware of – but also the acidification of the oceans’ surface waters.

The oceans play a fundamental role in evolutions of the Earth’s climate, getting involved in energy and mass transfer balance sheets with time constants which range from a month to a thousand years. A gigantic collector of this highly and naturally soluble gas, the sea world constitutes a safe in which is hoarded over 90% of carbon held by the whole of the continental ocean-atmosphere-biosphere. It is thus estimated that at least a quarter of the emissions due to human activities is rapidly absorbed by the ‘sponge’ that the oceans constitute. Over immense stretches of contact between the atmosphere and the sea there thus takes place, on a permanent basis, an essential process of CO₂ solubilisation. Once dissolved in the oceanic water mass, photosynthesised by phytoplankton and pulled along by the currents, the carbon thus enters the vast cycle of the multiple biological and chemical transformations of the undersea world, in which it becomes in a way ‘fixed’. CO₂ being chemically stable, its concentration in the atmosphere is the result of incessant exchanges between it and the other two huge carbon reservoirs, the continental biomass (vegetation) on the one hand, and the different carbonaceous compounds present in the sea on the other.