The influence of intertidal mudflats on the dissolved inorganic carbon and total alkalinity distribution in the German Bight, southeastern North Sea

Abstract

The distribution of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the German Bight, southeastern North Sea, was investigated during winter (February/March) 1996. Generally, high biological activity and riverine input dominate the carbon chemistry of this area for most of the year and mask impacts of other processes. During the investigation period, the presence of extended ice sheets, low river discharge and minimal primary productivity in the German Bight allowed the recognition of a considerable influence from sediment–water interaction. Water masses in front of the North Frisian Wadden Sea were clearly distinguished from others by considerably higher DIC and TA concentrations and a different DIC : TA ratio. We suggest that remineralisation products of Wadden Sea sediments and the DIC- and TA-enriched porewaters were subsequently released into the water column by enhanced erosion due to ice drift. The DIC : TA ratio of 1 : 1 indicates that either sulphate reduction or a combination of carbonate dissolution and aerobic remineralisation were the main processes generating this DIC. The calculated amount of DIC delivered from the Wadden Sea to the German Bight of about 10,000 t (equivalent to 76 mmol m −2 d −1) was in the same order of magnitude as the riverine input and about ten times higher than by diffusion alone. Apparently, for the carbon cycling in the coastal waters, sediment–water interaction may be a relevant process.