Accelerating CO2 outgassing in the equatorial Pacific from sat-ellite remote sensing

The equatorial Pacific serves as the largest oceanic source of CO₂. The contrasting ocean environment in the eastern (i.e., upwelling) and western (i.e., warm pool) regions makes it difficult to fully characterize the CO₂ dynamics with limited in situ observations.  In this study, we addressed this challenge using monthly surface partial pressure of CO₂ (pCO₂sw) and air–sea CO₂ fluxes (FCO₂) data products reconstructed from satellite and reanalysis data at spatial resolution of 1^°×1^° in the period of 1982–2021. We found that, during the very strong El Niño events (1997/1998, 2015/2016), both pCO₂sw and FCO₂ showed significant decrease of 41–58 μatm and 0.5–0.8 mol m^-2 yr^-1 in the eastern equatorial Pacific, yet remained at normal levels in the western equatorial Pacific. In contrast, during the very strong La Niña events (1999/2000, 2007/2008, and 2010/2011), both pCO₂sw and FCO₂ showed strong increase of 40–48 μatm and 1.0–1.4 mol m^-2 yr^-1 in the western equatorial Pacific, yet with little change in the eastern equatorial Pacific. In the past 40 years, pCO₂sw in the eastern equatorial Pacific was increasing at a higher rate (2.32–2.51 μatm yr^-1) than that in the western equatorial Pacific (1.75 μatm yr^-1), resulting in an accelerating CO₂ outgassing (at rate of 0.03 mol m^-2 yr^-2) in the eastern equatorial Pacific. We comprehensively analyzed the potential effects of different factors such as sea surface temperature, sea surface wind speed, and ΔpCO₂ in driving CO₂ fluxes in the equatorial Pacific, and found that ΔpCO₂ had the highest correlation (R ≥ 0.80, at p ≤ 0.05), highlighting the importance of accurate estimates of pCO₂sw from satellites.