Emergence of an oceanic CO uptake hole under global warming.

The ocean is a crucial sink for anthropogenic CO emissions, yet its future response remains uncertain. Here, using the Community Earth System Model (CESM2) under different CO emission rates, we find a pronounced weakening of ocean CO uptake in the Subpolar North Atlantic (SPNA), distinct from the global response. Initially, the SPNA is an effective CO sink, but due to the contraction of deep convection, the uptake decreases and the oceanic pCO exceeds the global average. Recognizing the importance of regional ocean circulation in CO 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 CO budget and geochemical environment, which is important for regional CO mitigation strategies.