Variability in the Subpolar Gyre circulation and throughput towards the Nordic Seas

The Atlantic Ocean exhibits a persistent northward heat transport at all latitudes, providing a key source of heat to the relatively northerly located European continent. Consequently, variability in the North Atlantic circulation plays a central role in modulating regional climate patterns in Europe. However, the widely reported lack of meridional coherence in the Atlantic basin on interannual to decadal timescales impedes the detection of large-scale circulation changes and their separation from internal climate variability. The Subpolar Gyre (SPG) is particularly important because variability in its circulation strength and hydrographic properties impacts both local dense water formation and heat transport towards the Arctic. In this study, we examine the structure and variability of the SPG circulation and quantify the recirculation within the gyre versus the throughput towards the Nordic Seas across the Greenland–Scotland Ridge. We employ the Lagrangian trajectory tool TRACMASS to identify the dominant pathways of recirculation and throughput, and quantify the associated volume and heat transports. We utilise a 1/12° ocean hindcast as Eulerian input fields for the period 1979–2021, and seed Lagrangian particles in the North Atlantic Current at 53°N. The Lagrangian trajectories allow us to quantify the spatio-temporal variability of the circulation, and to localise the depth- and density-dependent connectivity between the SPG and the Nordic Seas. The results lay the groundwork for a better understanding of the SPG as a potential modulator of heat transport towards the Arctic.