Basin‐Scale Estimate of the Sea‐Air CO₂ Flux During the 2010 Warm Event in the Tropical North Atlantic

Abstract

Following the anomalous warming event occurring in the tropical North Atlantic in 2010, higher than usual surface fugacity of CO 2 (fCO 2 ) was observed. To evaluate the spatial extent of these anomalies and their drivers, and to quantify the sea-air CO 2 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 fCO 2 recorded by two merchant ships. The anomalous warming of 2010 is well reproduced by the model and is the main driver of fCO 2 anomalies. The first coupled Empirical Orthogonal Function mode, between sea surface temperature and fCO 2 , captures more than 70% of the total variance and is characterized by a basin-scale warming associated to positive fCO 2 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 fCO 2 anomalies are primarily associated with sea surface salinity anomalies. Although the fCO 2 anomalies of 2010 appear mostly in spring, they affect the annual CO 2 budget and lead to an increased CO 2 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).

Disentangling the impact of Atlantic Niño on sea-air CO2 flux

“…The dominant role of SST and SSS in driving the sea-air CO 2 flux anomaly have been reported in a case study of warm SST anomaly event, observed from February to May in 2010, in the north tropical Atlantic, slightly to the north of the region in this study 32 – 34 . This warm SST anomaly event, however, is more related to the Atlantic Meridional Mode during spring while our investigated SST anomaly represents the Atlantic Zonal Mode during summer.…”

Evidence for enhanced primary production driving significant CO2 drawdown associated with the Atlantic ITCZ

“…Particularly notorious is the prolonged negative rainfall anomaly registered during late 2009 and early 2010. These were years of significant climatic anomalies in the tropical Atlantic, following the Pacific El Niño of 2009 (Ibánhez et al, 2017;Lefèvre et al, , 2019. During late 2008-early 2009, a positive anomaly in rainfall intensity is verified concomitant with a positive anomaly of wet dust deposition (Fig.…”

“…γ rain ) for each voyage used. 2017; Lefèvre et al, 2019) and strongly determines the seasonality observed. In between the SEC and the NEC and from June to November, the northward shift of the trade winds promotes the intensification of the NECC (Fonseca et al, 2004), which becomes visible in the eastward component of the surface velocity centered at about 5°-8°N along the tracks of the vessels used here (Fig.…”

“…Climate models project a weaker, narrower ITCZ due to anthropogenic warming (Byrne and Schneider, 2016b,a), adding to the impact of interannual climate modes over the rainfall regime of the tropical Atlantic (Lübbecke et al, 2018;Richter and Tokinaga, 2021). Increasing CO 2 outgassing caused by rising SST in the tropical Atlantic (Servain et al, 2014;Ibánhez et al, 2017;Lefèvre et al, 2019), would act together with the projected changes in the Atlantic ITCZ to further reduce the overall oceanic mitigation of anthropogenic CO 2 emissions to the atmosphere. Nevertheless, the interannual variability of sea-air CO 2 exchange and the impact of these projected changes over the CO 2 budget of the tropical Atlantic are poorly understood.…”

Comment on bg-2021-2

“…PISCES has been successfully used in a variety of biogeochemical studies, both at regional and global scale (Bopp et al, 2005;Gehlen et al, 2006Gehlen et al, , 2007Gutknecht et al, 2019;Lefèvre et al, 2019;Schneider et al, 2008;Séférian et al, 2013;Steinacher et al, 2010;Tagliabue et al, 2010).…”