Carbon dynamics in a productive coastal region—The Skagerrak

The importance of the coastal seas as areas of CO2 uptake from the atmosphere has gained more attention during recent years. This study utilizes dissolved inorganic carbon and hydrographic data collected in the Skagerrak for 10 months in 2006 to assess the carbon dynamics over the year. The surface water is under-saturated in CO2 relative to the atmosphere during the first half of the year and stays close to equilibrium at least until November. Consequently primary production compensates for the increase in pCO2 caused by the temperature increase from ∼ 2 to ∼ 10 °C in spring. Integrating the annual air–sea CO2 flux as computed using the Wanninkhof (1992) parameterization gives a net uptake of 1.2 mol m− 2 year− 1 which, if representative for the whole Skagerrak area, equals 3.7 ∙ 1010 mol year− 1 or 0.45 Tg C year− 1. Converting the nitrate consumption in the surface mixed layer from January to May to carbon units through the RKR ratio (Redfield et al., 1963) gives a drawdown of 6 g C m− 2. This number increases by a factor of two if primary productivity also occurs in the waters below the surface mixed layer, i.e. an increase in depth from 10 to 25 m as a seasonal average.We estimated the effect of salinity, biological processes and air–sea CO2 exchange on the monthly DIC change. We found that salinity was one of the major drivers for the DIC change.