Reconciling the role of the Labrador Sea overturning circulation in OSNAP and climate models

One paradigm of climate science is the important role of the Labrador Sea in shaping the evolution of the AMOC (Atlantic Meridional Overturning Circulation). This understanding is based largely on climate models as continuous, direct measurements of the overturning strength in the North Atlantic subpolar gyre (SPG) have remained, until recently, unavailable. However, a recent high profile observational campaign (Overturning in the Subpolar North Atlantic, OSNAP) has called into question the importance of the Labrador Sea, instead highlighting the magnitude of the overturning in the eastern SPG. Here, we reconcile these viewpoints by comparing the OSNAP data with a new, high-resolution coupled climate model: HadGEM3-GC3.1-MM. Unlike many previous models, we find our model compares well to the OSNAP overturning observations, with a similarly strong eastern/weak western SPG. Furthermore, overturning variability across OSNAP-E, and not in the Labrador Sea region, appears linked to AMOC variability further south. Labrador Sea densities are shown to be an important indicator of downstream AMOC variability, but these densities are driven by upstream variability across OSNAP-E rather than local processes in the Labrador Sea.