More Frequent and Enhanced Extreme Events of Air–Sea CO2 Fluxes

Abstract

The ocean is a crucial sink for anthropogenic CO2 and experiences various biogeochemical extremes, yet it is not clear whether and to what extent such extreme events occur in air–sea CO2 fluxes. Here, we established a framework to define oceanic carbon uptake extremes (CUXs) and release extremes (CRXs) using daily air–sea CO2 flux from both an observational‐based product and a state‐of‐the‐art Earth system model. Globally, cumulative CUX and CRX intensity over 1982–2022 were −0.14 and 0.14 Pg C yr−1, respectively, each accounting for ∼10% of the total oceanic CO2 uptake. The number of annual days and the absolute mean intensity of CUXs (CRXs) increase at rates of 1.22 d dec−1 (2.23 d dec−1) and 0.08 mol C m2 yr−1 dec−1 for both events. Under the high‐warming future scenario, these increasing trends are projected to accelerate, leading to a nearly five‐fold rise in the global cumulative intensity of CUXs and CRXs compared to the past four decades. After the 2050s, CRXs increase more rapidly than CUXs, especially in the Southern Ocean and North Atlantic, due to a reduced oceanic buffering capacity. Thermally driven seawater pCO2 dominates over half of the projected global CUX and CRX days, primarily in temperate oceans. The model also indicates shifts from nonthermal to thermal dominance in the tropical Pacific and Atlantic, the Indian Ocean, and the sporadic high‐latitude Southern Ocean, while the North Atlantic shows an opposite pattern. Our study shows that more frequent CRXs would further exacerbate the projected weakening in ocean carbon sinks.