ENSO Significantly Changes the Carbon Sink and Source Pattern in the Pacific Ocean with Regional Differences

The El Niño-Southern Oscillation (ENSO) alters ocean–atmosphere carbon exchange, but the mechanisms by which it affects the air–sea carbon flux (FCO2) remain unclear. Here, we used gridded FCO2 data from 2003 to 2021 to elucidate the control processes and regional differences in the influence of the ENSO on FCO2 in the mid–low latitude Pacific Ocean. Overall, the mid–low latitude Pacific Ocean region was a net sink for CO2, with an average uptake rate of −0.39 molC·m−2·year−1. Specifically, during the La Niña period in 2010–2012, the absorption rate decreased by 15.38%, while during the El Niño period in 2015–2016, it increased by 30.77%. El Niño (La Niña) suppressed (promoted) biological primary production in the North Pacific, leading to reduced (enhanced) carbon uptake. El Niño (La Niña) also inhibited (promoted) physical vertical mixing in the Equatorial Pacific, leading to reduced (enhanced) carbon emissions. In the South Pacific, however, El Niño increased carbon uptake and La Niña decreased carbon uptake; although, not by these two processes. More frequent El Niño in the future will further reduce carbon absorption in the North Pacific and carbon emission in the Equatorial Pacific but increase carbon absorption in the South Pacific.