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.