Fluxes of CO2 between the atmosphere and the ocean during the POMME project in the northeast Atlantic Ocean during 2001 : Subduction, water mass transformation, biochemical tracer distributions, and carbon cycle in the Northeast Atlantic Ocean at Mesoscale: The POMME Experiment

[1] In the eastern North Atlantic, carbon dioxide fugacity (fCO 2 ) in the upper mixed layer and discrete pH and total alkalinity measurements in the upper 2000 m were studied during three cruises (winter, spring, and summer 2001) within the framework of the Programme Ocean Multidisciplinaire Meso Echelle (POMME) project. This extensive region is located between 39° and 45°N and 16° and 21°W. The mesoscale variability of fCO 2 on the sea surface and in the atmosphere during each season was determined to understand the mechanisms of evolution that control the spatial and temporal variability of fCO 2 together with an estimation of the fluxes of CO 2 between the atmosphere and the ocean. If we consider the observation to be 22 days per cruise, the region was in-taking 0.30 Tg C during the winter cruise and 0.36 Tg C during the spring cruise, whereas it was out-gassing 0.07 Tg C during the summer cruise. These values are clear indications that the area is acting as a sink of CO 2 on an annual scale, with an estimated flux value of -1.1 mol m -2 yr -1 , which is over twice as much as the mean global flux of -0.5 mol m -2 yr -1 (Takahashi et al., 2002). The changes with time observed in the fCO 2 values over the surface layer between the winter and the spring cruises have been described considering thermodynamics, gas exchange, water transport, and biological activity in the area. The estimation of the subduction of inorganic carbon yielded a value of 0.25 Pg C yr -1 , which is approximately 10% of the global net oceanic CO 2 sink flux.