Impact of SST and ocean dynamics on the interannual variability of air-sea CO2 fluxes in the tropical Pacific

Ocean carbon uptake is crucial to mitigate carbon emissions due to human activities. The internal variability in air-sea CO2 fluxes (F-CO2) significantly affects the carbon budget assessment, especially in the tropical Pacific. However, the Coupled Model Intercomparison Project fails to capture real-world interannual variability of F-CO2, especially in the tropical Pacific. Based on observed sea surface temperature (SST) in the eastern tropical Pacific, the Pacific Ocean-Global Atmosphere (POGA) experiment reproduces real-world interannual variability in F(CO2 )consistent with observations in the tropical Pacific. The results show that this variability is dominated by El Ni & ntilde;o-Southern Oscillation (ENSO) events by Bjerknes feedback. Dynamic and thermodynamic decompositions further support the nonthermal processes that dominate the interannual variability of F-CO2, with stronger upwelling bringing higher dissolved inorganic carbon (DIC) from the subsurface to the surface, increasing the F-CO2 , and vice versa for downwelling. However, the SST thermal effect is opposite in phase to F(CO2 )changes, partly offsetting the effects of dynamic processes. Using the observed SST, the POGA experiment also extends the F(CO2 )datasets to the 1930s, partially overcoming the limitation of observations, and helping us understand interannual to decadal variability and vertical physical processes.