Air-Sea CO2 fluxes in the Atlantic as measured during boreal spring and autumn

• Published in: Biogeosciences
• Main Authors: Padin, X. A., Vázquez-Rodríguez, M., Castaño, M., Velo, A., Alonso-Pérez, F., Gago, J., Gilcoto, M., Álvarez, M., Pardo, P. C., Paz, M., Ríos, A. F., Pérez, F. F.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Drake Passage; Livingston Island; Southern Ocean; North Atlantic; North Atlantic oscillation
• Online Access: https://doi.org/10.5194/bg-7-1587-2010; https://www.biogeosciences.net/7/1587/2010/

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 Δ f CO 2 estimations with a mean difference of −3 ± 18 μatm (Takahashi et al., 2009). 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 long-term 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, 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.