Decadal changes of carbon dioxide in the Scheldt estuary

Since late 2002, we have carried continuous measurements of the partial pressure of CO2 (pCO2) at a fixed station in the upper Scheldt estuary, allowing a detailed description of the seasonal and inter-annual variability. This time-series reveals overall stable pCO2 conditions from 2003 to 2006, and a major decrease of pCO2 from late 2006 to early 2007 that is maintained during 2008 and 2009. To further investigate the propagation of these changes in the whole Scheldt estuary, we have carried out a monthly survey of pCO2 since January 2008 covering the estuary from freshwater to the mouth. Comparison with a similar monthly data-set obtained in 1997/1998, shows that a major decrease of pCO2 occurred in estuary in zone from 0 to 15 salinity. Drivers of these changes are discussed.