Carbon exchange in the North Atlantic
In line with the Kyoto Protocol, the assessment of carbon fluxes relies heavily on the reliable estimation of carbon budgets over different continental and oceanic regions. Until recently, estimates for inter-annual variability for air-sea CO2 fluxes in the North Atlantic were potentially contradictory. The conflict came from predictions coming from two different models, that is, inverse atmospheric models foresaw very large variability, while ocean models predicted a small variability in CO2 flux. Moreover, the large variability was also underpinned by data collected in the subtropical gyre of the North Atlantic. Based on the assumption that these data constituted a good representative sample, they were further extrapolated across the entire basin. On the basis of analysed simulations the NOCES project research work showed that the subtropical gyre wasn't representative of the entire North Atlantic. There were also multipolar anomalies at multiple frequencies in the sub-polar and inter-gyre regions. Thereby, being both high and low, these contributions displayed a tendency to cancel each other as far as the basin-wide air-sea CO2 flux was concerned. Within this context the NOCES project research offered a validated explanation on the reasons of disagreement between ocean and atmospheric inverse models. It was shown that atmospheric inverse models over-predict the variability of North Atlantic air-sea CO2 fluxes. On the other hand, the higher resolution of ocean models allows compensation of variability between regions, such as the sub-tropical and sub-polar gyres. The potential deficiencies of the inverse approach were mainly due to insufficient spatial resolution. Moreover, "leakage" of high variability from adjacent terrestrial grid cells also contributed to the high air-sea CO2 flux variability over the North Atlantic. Identification of the problematic areas of the atmospheric inverse approach and the mechanisms by which these may occur, eases the improvement of their future predictions. Furthermore, optimisation of the ocean component of coupled carbon-climate models is expected be exploited in the prediction of future changes in air-sea and air-land CO2 fluxes. For more project information, click at: http://www.ipsl.jussieu.fr/projets/NOCES/
