Emergence of an oceanic CO₂ uptake hole under global warming.

Abstract

The ocean is a crucial sink for anthropogenic CO₂ emissions, yet its future response remains uncertain. Here, using the Community Earth System Model (CESM2) under different CO₂ emission rates, we find a pronounced weakening of ocean CO₂ uptake in the Subpolar North Atlantic (SPNA), distinct from the global response. Initially, the SPNA is an effective CO₂ sink, but due to the contraction of deep convection, the uptake decreases and the oceanic pCO₂ exceeds the global average. Recognizing the importance of regional ocean circulation in CO₂ uptake, we identify a nonlinear relationship between environmental conditions and uptake response, revealing consistent thresholds for the emergence of uptake weakening. These findings are also reproduced in the Coupled Model Intercomparison Project Phase 6, confirming their robustness. Overall, the distinct uptake response reflects the key role of regional dynamics in regulating the CO₂ budget and geochemical environment, which is important for regional CO₂ mitigation strategies.