Overturning Variations in the Subpolar North Atlantic in an Ocean Reanalyses Ensemble

The ocean’s Atlantic Meridional Overturning Circulation (AMOC) has a significant influence on global climate through its meridional transport of heat and carbon. Deep water formation occurring in the subpolar North Atlantic is an essential component the AMOC. Understanding the nature and causes of its multidecadal variation at these high latitudes is critical to more accurately predict future changes. We analyse the subpolar overturning in an ensemble of eddy permitting ¼ degree global ocean reanalyses, restrained by observations and historical forcings, over the period 1993-2018. This overturning transport is validated against the continuous measurements obtained along the Overturning in the Subpolar North Atlantic Program (OSNAP) mooring array since 2014. The ability of each reanalysis to capture the observed changes in the overturning will be determined, providing confidence in their ability to simulate changes prior to the availability of OSNAP, and exposing their limitations. We analyse the eastern and western sections of the OSNAP array to determine the relative importance of the overturning along these sections and the temporal variability on various timescales. This research complements a previous study investigating changes in the subtropical Atlantic overturning using the same reanalyses ensemble which was shown to provide a good approximation to observations.