CO2 partial pressure in Northeast Atlantic and adjacent shelf waters: Processes and seasonal variability

Abstract CO 2 partial pressure in surface water was measured in the Northeast Atlantic and in the Hebride Shelf/North Sea area during a cruise with R.V. Poseidon in June 1991. A mean p CO 2 of 303 μatm was found in the Atlantic between 50°N and 60°N. For an atmospheric CO 2 content of 357.5 ppm(v) this corresponds to a partial pressure difference of −55 μatm. This supports the view that the subarctic Atlantic is a significant sink within the CO 2 cycle between the ocean and the atmosphere. A comparison of our measurements with other data reveals that the p CO 2 distribution changes significantly during May/June. This explained by seasonal warming, CO 2 exchange with the atmosphere and biomass production. The contribution by each of these processes to the seasonal variations is calculated. It was found that during a plankton bloom the production of biomass is the dominating factor and may lower seawater p CO 2 by almost 100 μatm. The shelf areas are charactrized by strong p CO 2 gradients which are explained by water exchange with the Atlantic, temperature effects and biomass production.