Surface predictor of overturning circulation and heat content change in the subpolar North Atlantic

In the North Atlantic, the northward transport of warm surface waters compensated for by the southward transport of cold deep water – the Atlantic Meridional Overturning Circulation (AMOC) – is tightly linked to the rates at which warm waters are being transformed into colder ones through buoyancy exchanges at the air-sea interface. The large-scale meridional heat transport associated with this transformation is a primary driver of temperature variability in the North Atlantic, and models have particularly suggested its important role in the warming (1993-2005) to cooling (2005-2017) reversal recently observed in the subpolar gyre. Here, we present a validation of those theoretical and model-based inferences on the AMOC thermodynamics and its impact on ocean temperature during 1993-2017 from a combination of ocean and atmosphere observational products. We find that surface-forced water mass transformation led AMOC variability at 45°N by 5 years and drove its 1993-2010 decline and the associated bi-decadal warming-to-cooling reversal of the upper ocean. We then build on the 5-year time-lag between surface-forced water mass transformation and AMOC variability to suggestively predict extreme AMOC intensities for the early 2020’s and an upcoming new climatic reversal towards warming conditions in the subpolar gyre.