Modeling the carbon fluxes of the northwest European continental shelf: Validation and budgets

Carbon budgets are simulated for the northwest European continental shelf and adjacent regions of the northeast Atlantic. Both physical and biological processes are evaluated, including exchanges between the water column and the atmosphere and sea bed. We use a multi-year simulation of a coupled 3D hydrodynamics-ecosystem model (POLCOMS-ERSEM) driven by realistic atmospheric data, ocean boundary conditions and freshwater inputs for 1989 to 2004. The northeast Atlantic (20°W to 13°E, 40°N to 65°N), including the European shelf, is found to be a net sink for atmospheric CO2. Biological processes exert a stronger control over pCO2 than temperature, and hence have a stronger effect on the air-sea CO2 exchange. For the European shelf, carbon sources of rivers and the uptake of atmospheric CO2 are balanced by horizontal transport off shelf and there is little carbon burial. There is net transport of carbon onto the shelf in the top 180 m of the water column and off the shelf below that depth, with a net carbon loss of ∼6 ± 1 × 1012 mol C yr−1. Up to 50% of the carbon exported from the shelf is transported below the permanent pycnocline and so is isolated from release into the atmosphere on centennial timescales.