Heat Storage Pattern Linked to the Atlantic Meridional Overturning Circulation Slowdown

Abstract

The Atlantic Ocean has absorbed ∼30% of Earth's excess heat under anthropogenic warming and witnessed enhanced warming since the mid-20th century. Yet, mechanisms governing the Atlantic warming, particularly the role of Atlantic Meridional Overturning Circulation (AMOC), remain uncertain. Through ocean-only and coupled model experiments, we confirm the key role of the weakened AMOC in the enhanced Atlantic heat storage. Physically, the reduced poleward heat transport of AMOC causes an additional heat pile-up in the 15°S–45°N regions with a lag time of ∼10 years. Based on this dynamical linkage, we propose that the regional enhanced heat storage in the 15°S–45°N Atlantic relative to the global average serves as a fingerprint for the long-term AMOC change. The observed heat storage indicates an overall AMOC slowdown by only 1.31 ± 0.39 Sv since the 1950s. Considering the pronounced natural variability, this weak anthropogenic AMOC slowdown probably has not emerged yet.