First direct estimates of volume and water mass transports across the Reykjanes Ridge

The Reykjanes Ridge, the northern section of the Mid-Atlantic Ridge, strongly influences the cyclonic circulation of the North Atlantic subpolar gyre, a major component of the climate system. Up to now, no dedicated data set was available to describe the circulation across this ridge. To fill this gap, surface-to-bottom measurements of flow velocity and water mass properties were carried out along the crest of the ridge, from Iceland to 50°N, in 2015. North of 53.15°N, the flow was mainly westward. It defines the westward branch of the subpolar gyre, and our study provides the first direct estimate of its intensity. The westward flow followed two main pathways related to specific bathymetry features: at the Bight Fracture Zone (57°N), which is a deep opening in the ridge, and at 59–62°N where the bathymetry rapidly deepens southward. The horizontal circulation of the Iceland Basin connects these pathways to the North Atlantic Current flowing eastward south of 53.15°N. Knowledge of the westward cross-ridge flows is a prerequisite for understanding the northward evolution of the Irminger Current, a major conduit for the subtropical waters toward the deep convection regions in the Irminger and Labrador Seas.