Weakened Atlantic meridional overturning circulation redistributes heat from Atlantic to Indo-Pacific and enhances global ocean heat uptake efficiency

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) has a dramatic impact on global ocean heat uptake and redistribution. Here, we isolate and quantify this AMOC impact using free- and fixed-AMOC climate model simulations. During the last four decades, the weakened AMOC has moved heat from the subpolar North Atlantic to the lower-latitude Atlantic and South Atlantic, while may not fully across the Indo-Pacific. By the end of the twenty-first century, AMOC-induced signals in forms of oceanic Kelvin and Rossby waves will travel across the Indo-Pacific, causing basin-wide warming. The weakened AMOC creates an Atlantic heat linkage to the Southern Ocean. Meanwhile, the Southern Ocean’s surface warms as part of the bipolar-seesaw response, and its top 1500 m warms as well as a result of subduction of warmer surface water mass. The warmed Southern Ocean then transports heat northward into the Indo-Pacific and spreads it over the majority of the basin via an anomalous anticlockwise MOC there. Basin-integrated ocean heat budgets unravel the Southern Ocean’s “mediator” role in redistributing rather than storing heat. Between 1980 and 2100, the weakened AMOC leads to ocean heat uptake but surface cooling in terms of global average, hence significantly promotes ocean heat uptake efficiency.