Indo-Pacific Warming Induced by a Weakening of the Atlantic Meridional Overturning Circulation

Abstract

Abstract The reorganization of the Atlantic meridional overturning circulation (AMOC) is often associated with changes in Earth’s climate. These AMOC changes are communicated to the Indo-Pacific basins via wave processes and induce an overturning circulation anomaly that opposes the Atlantic changes on decadal to centennial time scales. We examine the role of this transient, interbasin overturning response, driven by an AMOC weakening, both in an ocean-only model with idealized geometry and in a coupled CO2 quadrupling experiment, in which the ocean warms on two distinct time scales: a fast decadal surface warming and a slow centennial subsurface warming. We show that the transient interbasin overturning produces a zonal heat redistribution between the Atlantic and Indo-Pacific basins. Following a weakened AMOC, an anomalous northward heat transport emerges in the Indo-Pacific, which substantially compensates for the Atlantic southward heat transport anomaly. This zonal heat redistribution manifests as a thermal interbasin seesaw between the high-latitude North Atlantic and the subsurface Indo-Pacific and helps to explain why Antarctic temperature records generally show more gradual changes than the Northern Hemisphere during the last glacial period. In the coupled CO2 quadrupling experiment, we find that the interbasin heat transport due to a weakened AMOC contributes substantially to the slow centennial subsurface warming in the Indo-Pacific, accounting for more than half of the heat content increase and sea level rise. Thus, our results suggest that the transient interbasin overturning circulation is a key component of the global ocean heat budget in a changing climate.