Observed variability of the North Atlantic Current in the Rockall Trough, at the crossroad between the subpolar gyre and the Nordic Seas.

The Rockall Trough is one of the main pathways of 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. However, the precise role of the Rockall Trough in the propagation of these anomalies is currently unknown.

As part of OSNAP, a mooring array was deployed in the Rockall Trough in order to obtain the first multi-year continuous measurements of the Rockall Trough poleward transport. During the 2014-2018 period, the 4-year mean transport from the mooring array (3.7 Sv, standard error of 0.5 Sv) is close to previous estimates based on several decades of repeated hydrographic sections. With most of the transport located in the upper 1000m, the mean northward transport in the Rockall Trough can contribute to 100% of the Atlantic inflow of warm water in the Faroe-Shetland Channel but also to a fraction of the Iceland-Faroe Atlantic inflow.

The existence of surface and subsurface pathways linking the Rockall Trough and the Iceland Basin through 1200m-deep channels is confirmed through the joint analysis of satellite altimetry, surface drogued drifters, Argo floats trajectories and the new OSNAP mooring observations presented in this study. The large variability in our transport time-series (ranging from -2.0 Sv to 11.1 Sv) is linked to changes in the Absolute Dynamic Topography slopes over these 1200m-deep channels located north of the Rockall Trough and to increase or decrease of the Atlantic Water inflow in the Nordic Seas through the Faroe-Shetland Channel. Therefore, the Rockall Trough can be seen as a primary conduit for the northward flux of warm waters in the Nordic Seas, particularly from 2014 to 2018.

With an increased risk of an ice-free Arctic in summer within the next 20–30 years, we anticipate our results to be a starting point for further process studies on the propagation of ocean heat anomalies toward the Arctic.