Assessment of the processes controlling the seasonal variations of dissolved inorganic carbon in the North Sea

Abstract

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO 2 ( p CO 2 ), and inorganic nutrients to assess the abiotic and biological processes governing the monthly variations of DIC. During winter, advection and air‐sea exchange of CO 2 control and increase the DIC content in the surface and deeper layers of the northern and central North Sea, with the atmosphere supplying CO 2 on the order of 0.2 mol C m −2 month −1 to these areas. From February to July, net community production (NCP) controls the seasonal variations of DIC in the surface waters of the entire North Sea, with a net uptake ranging from 0.5 to 1.4 mol C m −2 month −1 . During the August‐December period, NCP controls the seasonal variations of DIC in the southern North Sea, with a net release ranging from 0.5 to 0.8 mol C m −2 month −1 . Similarly, during the April‐August period in the deeper layer of the northern North Sea, the NCP was the main factor controlling DIC concentrations, with a net release ranging from 0.5 to 5.5 mol C m −2 month −1 . In the surface layer of the North Sea, NCP on the basis of DIC was 4.3 ± 0.4 mol C m −2 yr −1 , whereas, NCP on the basis of nitrate was 1.6 ± 0.2 mol C m −2 yr −1 . Under nutrient‐depleted conditions, preferential recycling (extracellular) of nutrients and intracellular mechanisms occurred and were responsible for the non‐Redfield uptake of DIC versus nitrate and phosphate.

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