Dynamics and Temporal Variability of the North Atlantic Current in the Iceland Basin, North Atlantic (2014 to 2022)

The North Atlantic Current (NAC) is a major source of heat towards the subpolar gyre and northern seas. However, its variability and drivers are not well understood. Here, we evaluated 8 years of continuous daily measurements as part of the international programme Overturning in the Subpolar North Atlantic Program (OSNAP) to investigate the NAC in the Iceland Basin. We found that the NAC volume and freshwater anomaly transport and heat content were highly variable, with significant variability at time scales of 16-120 days to annual. The shorter time scales were associated with mesoscale features abundant in the region. Composites analysis revealed that strong NAC periods were associated with a westward migration of the eastern boundary of the subpolar North Atlantic (SPNA) gyre and less eddy kinetic energy in the Iceland Basin, which was consistent with the presence of frontal-like structures instead of eddy-like structures. Stronger zonal wind stress triggers a fast response that piles water up between the SPNA and subtropical gyres which increases the sea surface height gradient and drives the acceleration of the NAC. The strengthening of the NAC increases the heat and salt transport northward. During our study period, both heat and salt increased across the moorings. These observations are important for understanding the heat and freshwater variability in the SPNA, which ultimately impact the Atlantic Meridional Overturning Circulation.