A paper in the Journal of Geophysical Research by Dr Ute Schuster and Professor Andrew Watson of the University of East Anglia (UK) raises concerns that the oceans might be slowing their uptake of CO2.
Results of their decade-long study in the North Atlantic show that the uptake in this ocean, which is the most intense sink for atmospheric CO2, slowed down dramatically between the mid-nineties and the early 2000s. An earlier study had already identified a slowdown in the sink in the Southern Ocean (earlier post), but the change in the North Atlantic is greater and more sudden, and could be responsible for a substantial proportion of that observed weakening.
The observations were made from merchant ships equipped with automatic instruments for measuring carbon dioxide in the water. Much of the data has come from a container ship carrying bananas from the West Indies to the UK, making a round-trip of the Atlantic every month. The MV Santa Maria, chartered by Geest, has generated more than 90,000 measurements of CO2 in the past few years.
The results show that the uptake by the North Atlantic halved between the mid-90s, when data was first gathered, and 2002-05.
Such large changes are a tremendous surprise. We expected that the uptake would change only slowly because of the ocean’s great mass. We are cautious about attributing this exclusively to human-caused climate change because this uptake has never been measured before, so we have no baseline to compare our results to. Perhaps the ocean uptake is subject to natural ups and downs and it will recover again.—Ute Schuster
The direction of the change was worrying, she added, and there were some grounds for believing that a saturation of the ocean sink would start to occur.
The speed and size of the change show that we cannot take for granted the ocean sink for the carbon dioxide. Perhaps this is partly a natural oscillation or perhaps it is a response to the recent rapid climate warming. In either case we now know that the sink can change quickly and we need to continue to monitor the ocean uptake.—Andrew Watson
Schuster, U., and A. J. Watson (2007), “A variable and decreasing sink for atmospheric CO2 in the North Atlantic”, J. Geophys. Res., doi:10.1029/2006JC003941, in press