Abstract.A total of fourteen hydrographic cruises from 2000 to 2008 were conducted during the spring and autumn seasons between Spain and the Southern Ocean under the framework of the Spanish research project FICARAM. The underway measurements were processed and analysed to describe the meridional air-sea CO 2 fluxes (F CO 2 ) in the covered sector of the Atlantic Ocean. The data has been grouped into different biogeochemical oceanographic provinces based on thermohaline characteristics. The spatial and temporal distributions of F CO 2 followed expected distributions and annual trends reproducing the recent climatological f CO 2 estimations with a mean difference of −3 ± 18 µatm . The reduction in the CO 2 saturation along the meridional FICARAM cruises represented an increase of 0.02 ± 0.14 mol m −2 yr −1 in the ocean uptake of atmospheric CO 2 . The subtropical waters in both Hemispheres acted as a sink of atmospheric CO 2 during the successive spring seasons and as a source in autumn. The coarse reduction of the ocean uptake of atmospheric CO 2 observed in the North Atlantic Ocean was linked to conditions of negative phase of the North Atlantic Oscillation that prevailed during the FICARAM period. Surface waters in the North Equatorial Counter Current revealed a significant longterm decrease of sea surface salinity of −0.16 ± 0.01 yr −1 coinciding with a declination of −3.5 ± 0.9 µatm yr −1 in the air-sea disequilibrium of CO 2 fugacity and a rise of oceanic CO 2 uptake of −0.09 ± 0.03 mol m −2 yr −1 . The largest CO 2 source was located in the equatorial upwelling system. These tropical waters that reached emissions of 0.7 ± 0.5 and 1.0 ± 0.7 mol m −2 y −1 in spring and autumn, respectively, Correspondence to: X. A. Padin (padin@iim.csic.es)showed an interannual warming of 0.11 ± 0.03 • C yr −1 and a wind speed decrease of −0.58 ± 0.14 m s −1 yr −1 in spring cruises which suggest the weakening of upwelling events associated with warm El Niño -Southern Oscillation episodes. Contrary the surface waters of the Patagonian Sea behaved as an intense sink of CO 2 in March and November. The oceanic waters of the convergence of Falkland and Brazil Currents showed the strongest CO 2 absorption with a rate of −5.4 ± 3.6 mol m −2 yr −1 in November. The Southern Oceans sampled in the Drake Passage behave as an average uptake rate of −1.1 ± 0.9 mol m −2 yr −1 while the distal shelf of the Livingston Island acted as a slight source of CO 2 to the atmosphere.

Abstract. A total of fourteen hydrographic cruises spanning from 2000 to 2008 were conducted during the spring and autumn seasons between Spain and the Southern Ocean, under the framework of the Spanish research project FICARAM. The performed underway measurements are processed and analysed to describe the meridional air-sea CO2 fluxes (FCO2) along the Atlantic Ocean. The data was organised into different biogeochemical oceanographic provinces, according mainly to the thermohaline characteristics. The obtained spatial and temporal distributions of FCO2 follow the generally expected patterns and annual trends. The Subtropical regions in both hemispheres alternated the CO2 source and sink nature from autumn to spring, respectively. On the other hand, Tropical waters and the Patagonian Sea clearly behaved as sinks of atmospheric CO2 like the waters of the Drake Passage during autumn. The obtained results during the cruises also revealed significant long-term trends, such as the warming of equatorial waters (0.11±0.03°C yr−1) and the decrease of surface salinity (−0.16±0.01 yr−1) in tropical waters caused by the influence of the Amazon River plume. This reduction in surface salinity appears to have a direct influence over the CO2 storage rates, fostering the uptake capacity of atmospheric CO2 (−0.09±0.03 mol m−2 yr−1). An analysis of the biogeochemical forcing on the CO2 fugacity (fCO2) variability performed from an empirical algorithm highlighted the major role of the Amazon River input in the tropical North Atlantic fluxes. In addition, it has provided a quantitative measure of the importance of the thermodynamic control of FCO2 at temperate latitudes.

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