Coherence of the AMOC Over the Subpolar North Atlantic on Interannual to Multiannual Time Scales

Direct measurements of the Atlantic Meridional Overturning Circulation (AMOC) are necessary to understand its evolution in a context of climate change. International programs monitored its recent evolution at different latitudes. However, the AMOC coherence over the North Atlantic remains unclear. Here, we explore the potential of the Overturning in the Subpolar North Atlantic Programme (OSNAP) array to inform us on mid-latitude AMOC strength on interannual-to-multiannual timescales in two high-resolution coupled models. We find that the AMOC strength measured at OSNAP is not related to the variability of the AMOC strength at mid-latitudes. Instead, our study reveals that the density at which the maximum overturning occurs at OSNAP is a key precursor of the mid-latitude AMOC strength. The causal relationship between AMOC density at the OSNAP array and AMOC strength at 45°N is linked to an atmospherically driven shoaling of isopycnal surfaces that propagates along the western boundary in a year.