Atlantic Meridional Overturning Circulation

The Atlantic Meridional Overturning Circulation (AMOC) is the basin-scale component of the global thermohaline circulation that transports warm, salty surface water northward in the Atlantic and returns cold, deep water southward. It is the most studied and potentially the most vulnerable of the ocean's overturning cells, and its strength is a sensitive function of the density contrast between the subtropical surface and the subpolar deep.

The AMOC is not merely a conveyor belt. It is a coupled atmosphere-ocean-ice system that responds to freshwater forcing, wind stress, and atmospheric heat flux. Its weakening or reorganisation would alter heat transport, sea level patterns, and marine ecosystems across the entire Atlantic basin. Observational evidence suggests a 15% decline since the mid-20th century, though the signal is contested against the background of natural variability.

The AMOC has been linked to abrupt climate changes in the paleoclimate record, including the Younger Dryas and Heinrich events. Its potential future weakening is one of the most consequential uncertainties in climate projections, with implications for European climate, tropical monsoon systems, and global sea level.

Ocean Heat Transport is the broader physical process that the AMOC exemplifies, and its study requires understanding the interaction between baroclinic instability and the mean circulation.