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.

The Rockall Trough is one of the main conduits for warm Atlantic Water to the Nordic Seas. Ocean heat anomalies, originating from the eastern subpolar gyre, are known to influence Arctic sea ice extent, marine ecosystems, and continental climate. Knowledge of the transport through this basin has previously been limited to estimates from hydrographic sections which cannot characterise the intra‐annual and multi‐annual variability. As part of the Overturning in the Subpolar North Atlantic Programme (OSNAP), a mooring array was deployed in the Rockall Trough in order to obtain the first continuous measurements of transport. Here, we define the methodology and the errors associated with estimating these transports. Results show a 4‐year mean northward transport of 6.6 Sv (1 Sv = 106 m3/s) by the North Atlantic Current (NAC) in the east and interior of the Rockall Trough (2014‐2018). A mean transport of ‐2.0 Sv (southward) is observed in the west of the basin, which could be part of a recirculation around the Rockall Plateau. The 90‐day low‐pass filtered transport shows large sub‐annual and inter‐annual variability (‐1.6 Sv to 9.1 Sv), mostly resulting from changes in the mid‐basin geostrophic transport. Satellite altimetry reveals the periods of low and high transport are associated with significant changes in the Rockall Trough circulation. There is a detectable seasonal signal, with the greatest transport in spring and autumn.