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 in 2023, this suppression was weaker than during the previous major El Niño events of 1997–1998 and 2015–2016 (hereafter referred to as 1997/2015), despite comparable levels of surface warming. Focusing on a single GOBM, we show that during 1997/2015, strong warming coincided with a weakening of westerly winds and sharply reduced equatorial upwelling, causing pronounced outgassing suppression. In contrast, although warming in 2023 was similarly strong, the westerly wind anomaly and upwelling reduction were not as strong as during the previous 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.

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