The Irminger Gyre as a key driver of the subpolar North Atlantic overturning on monthly timescales

The lower limb of the Atlantic meridional overturning circulation (AMOC) is the equatorward flow of dense waters that have been transformed due to the cooling and freshening of the poleward-flowing upper limb. In the subpolar North Atlantic (SPNA), upper limb variability is primarily set by the North Atlantic Current, whereas lower limb variability is less well understood, particularly at subseasonal timescales. Using observations from a SPNA mooring array, we show that variability of the AMOC’s lower limb is connected to poleward flow in the interior Irminger Sea. We identify this flow as the northward branch of the Irminger Gyre (IG), accounting for 55% of the AMOC’s lower limb variability on monthly timescales. Further, wind stress curl fluctuations over the Labrador and Irminger Seas drives the IG and AMOC variability on monthly timescales. On interannual timescales, however, increasing thickness of intermediate water within the Irminger Sea coincides with decreasing IG recirculation.