Muted Tropical Pacific Ocean Carbon Response to the 2023 Extreme El Niño

El Niño dominates the interannual variability of global air-sea CO₂ fluxes by suppressing CO₂ outgassing in the tropical Pacific. Using an ensemble of observation-based fCO₂ products and global ocean biogeochemical models (GOBMs), we find that the 2023 El Niño produced an anomalously weak carbon-cycle response. CO₂ outgassing was reduced by only about 0.1 Pg C yr⁻¹, roughly half of the 0.18 Pg C yr⁻¹ reduction expected from the historical SST–carbon relationship established during the extreme 1997–1998 and 2015–2016 El Niño events (hereafter 1997/2015). We show that although warming in 2023 was similarly strong, the westerly wind anomaly and upwelling reduction were not as strong as during the previous extreme El Niño events. Consequently, the non-thermal ocean pCO₂ decrease was smaller than in 1997/2015, while the thermal anomaly remained comparable, limiting the net pCO₂ response. In addition, the comparably high wind speeds facilitated high gas-exchange rates, which further prevented the suppression of CO₂ outgassing. These findings highlight the variability and complexity of the canonical El Niño-carbon coupling and call for improved theoretical, modeling, and observational constraints.