Decreases in South Pacific and South Atlantic sea-air CO2 fluxes caused by extreme precipitation

Extreme precipitation intensifies under global warming, yet its impact on sea-air CO2 flux (FCO2) remains underexplored. Here we show that the maximum 1-day precipitation (Rx1day) exerts a notable influence on FCO2 in the South Pacific Ocean and South Atlantic Ocean during 1990–2023. An increase in Rx1day from 0 to 30 mm causes the South Pacific Ocean and South Atlantic Ocean to shift from carbon sources to carbon sinks, with FCO2 decreasing from 96 to −27 mmol m−2 month−1 and from 70 to −70 mmol m−2 month−1, respectively. This reduction is likely attributed to precipitation-induced dilution effects on salinity and alkalinity. When precipitation increases by up to 20%, FCO2 exhibits maximum reductions of 27% (5.6 mmol m−2 month−1) in the South Pacific Ocean and 10% (6.4 mmol m−2 month−1) in the South Atlantic Ocean. Neglecting precipitation may result in a non-negligible overestimation of FCO2, underscoring the necessity of incorporating it into ocean carbon budget models. Maximum 1-day precipitation affects the sea-air CO2 flux of the South Pacific Ocean and South Atlantic Ocean. Incorporating precipitation into ocean carbon budget models is critical for the accurate estimation of sea-air CO2 flux.