Carbon dioxide uptake by a temperate tidal sea

Carbon dioxide (CO2) exchange between the atmosphere and the Wadden Sea, a shallow coastal region along the northern Netherlands, has been measured from April 2006 onwards on a tidal flat and over open water. Tidal flat measurements were done using a flux chamber, and ship borne measurements using an equilibrator to determine the partial pressure Of CO2 in the water. A strong response Of CO2 exchange rate on irradiance changes was observed at the tidal flat surface, with generally strong uptake Of C02 during daylight conditions and release, presumably due to respiration, during dark conditions. The rate of respiration appeared to increase with temperature. Daytime CO2 uptake tended to be higher than nighttime release all year round. Apparently, tidal flats in temperate regions of the globe may be a sink for CO2 on an annual basis. In contrast to terrestrial CO2 exchange, uptake by processes active on and in tidal flats responds only slowly to changing irradiance. This slow reaction is attributed to CO2 storage in wet soil. Measurements in the water between tidal flats suggest that the estuarine, open water part of the Wadden Sea is a source of CO2 in spring.