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Following the anomalous warming event occurring in the tropical North Atlantic in 2010, higher than usual surface fugacity of CO2 (fCO2) was observed. To evaluate the spatial extent of these anomalies and their drivers, and to quantify the sea‐air CO2 flux at basin scale, the Mercator‐Ocean model is used from 2006 to 2014 within the region 0–30°N, 70–15°W. Model outputs are generally in accordance with underway sea surface temperature, sea surface salinity, and surface fCO2 recorded by two merchant ships. The anomalous warming of 2010 is well reproduced by the model and is the main driver of fCO2 anomalies. The first coupled Empirical Orthogonal Function mode, between sea surface temperature and fCO2, captures more than 70% of the total variance and is characterized by a basin‐scale warming associated to positive fCO2 anomalies. The corresponding principal components are correlated to the Tropical North Atlantic Index and identify 2010 as the year with the highest positive anomaly over 2006–2014. Exceptions to this general pattern are located near the African coast, where the weakening of the coastal upwelling causes negative inorganic carbon anomalies, and close to the Amazon River plume, where fCO2 anomalies are primarily associated with sea surface salinity anomalies. Although the fCO2 anomalies of 2010 appear mostly in spring, they affect the annual CO2 budget and lead to an increased CO2 outgassing twice as large (46.2 Tg C per year) as the mean annual flux over the 2006–2014 period (23.3 Tg C per year). Key Points: Underway fCO2 observations of 2010, collected on two merchant ships, compare well with the Mercator‐Ocean model simulationsThe fCO2 anomalies observed in Spring 2010 in the tropical North Atlantic are mostly driven by the sea surface temperature anomaliesThe resulting outgassing of CO2 for the year 2010 is twice as large as the mean sea‐air CO2 flux over the 2006 to 2014 period [ABSTRACT FROM AUTHOR]

CO2 fugacities obtained from a merchant ship sailing from France to French Guyana were used to explore the seasonal and interannual variability of the sea-air CO2 exchange in the western tropical North Atlantic (TNA; 5-14°N, 41-52°W). Two distinct oceanic water masses were identified in the area associated to the main surface currents, i.e., the North Brazil Current (NBC) and the North Equatorial Current (NEC). The NBC was characterized by permanent CO2 oversaturation throughout the studied period, contrasting with the seasonal pattern identified in the NEC. The NBC retroflection was the main contributor to the North Equatorial Counter Current (NECC), thus spreading into the central TNA, the Amazon River plume, and the CO2-rich waters probably originated from the equatorial upwelling. Strong CO2 undersaturation was associated to the Amazon River plume. Total inorganic carbon drawdown due to biological activity was estimated to be 154 µmol kg−1 within the river plume. As a consequence, the studied area acted as a net sink of atmospheric CO2 (from −72.2 ± 10.2 mmol m−2 month−1 in February to 14.3 ± 4.5 mmol m−2 month−1 in May). This contrasted with the net CO2 efflux estimated by the main global sea-air CO2 flux climatologies. Interannual sea surface temperature changes in the TNA caused by large-scale climatic events could determine the direction and intensity of the sea-air CO2 fluxes in the NEC. Positive temperature anomalies observed in the TNA led to an almost permanent CO2 outgassing in the NEC in 2010. [ABSTRACT FROM AUTHOR]