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

[摘要] A total of fourteen hydrographic cruises from 2000 to 2008were conducted during the spring and autumn seasons between Spain and theSouthern Ocean under the framework of the Spanish research project FICARAM.The underway measurements were processed and analysed to describe themeridional air-sea CO₂ fluxes (FCO₂) in the covered sector of theAtlantic Ocean. The data has been grouped into different biogeochemicaloceanographic provinces based on thermohaline characteristics. The spatialand temporal distributions of FCO₂ followed expected distributions andannual trends reproducing the recent climatological ΔfCO₂estimations with a mean difference of −3 ± 18 μatm (Takahashi etal., 2009). The reduction in the CO₂ saturation along the meridionalFICARAM cruises represented an increase of 0.02 ± 0.14 mol m⁻² yr⁻¹in the ocean uptake of atmospheric CO₂. The subtropicalwaters in both Hemispheres acted as a sink of atmospheric CO₂ duringthe successive spring seasons and as a source in autumn. The coarsereduction of the ocean uptake of atmospheric CO₂ observed in the NorthAtlantic Ocean was linked to conditions of negative phase of the NorthAtlantic Oscillation that prevailed during the FICARAM period. Surfacewaters in the North Equatorial Counter Current revealed a significantlong-term decrease of sea surface salinity of −0.16 ± 0.01 yr⁻¹coinciding with a declination of −3.5 ± 0.9 μatm yr⁻¹ in theair–sea disequilibrium of CO₂ fugacity and a rise of oceanic CO₂uptake of −0.09 ± 0.03 mol m⁻² yr⁻¹. The largest CO₂source was located in the equatorial upwelling system. These tropical watersthat reached emissions of 0.7 ± 0.5 and 1.0 ± 0.7 mol m⁻² y⁻¹in spring and autumn, respectively, showed an interannual warmingof 0.11 ± 0.03 °C yr⁻¹ and a wind speed decrease of −0.58 ± 0.14 m s⁻¹ yr⁻¹in spring cruises which suggest the weakening ofupwelling events associated with warm El Niño – Southern Oscillationepisodes. Contrary the surface waters of the Patagonian Sea behaved as anintense sink of CO₂ in March and November. The oceanic waters of theconvergence of Falkland and Brazil Currents showed the strongest CO₂absorption 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 uptakerate of −1.1 ± 0.9 mol m⁻² yr⁻¹ while the distal shelf of theLivingston Island acted as a slight source of CO₂ to the atmosphere.

[学科分类] 地球化学与岩石