First Direct Estimates of Volume and Water Mass Transports Across the Reykjanes Ridge

Abstract

The Reykjanes Ridge is a major topographic feature located south of Iceland in the North Atlantic Ocean that strongly influences the subpolar gyre circulation. Based on velocity and hydrographic measurements carried out along the crest of the Reykjanes Ridge from the Icelandic continental shelf to 50°N during the RREX cruise in June–July 2015, we derived the first direct estimates of volume and water mass transports over the Reykjanes Ridge. North of 53.15°N, circulation was mainly westward; south of this latitude it was mainly eastward. The westward transport was estimated at 21.9 ± 2.5 Sv (Sv = 106 m3 s−1) and represents the subpolar gyre intensity. The westward flows followed two main pathways at 57°N near the Bight Fracture Zone and at 59–62°N. We argue that those pathways were connected to the northern branch of the North Atlantic Current and to the Sub-Arctic Front, respectively, which were both intersected by the southern part of the section. In addition to this horizontal circulation, mixing and bathymetry shaped the water mass distribution. Water mass transformations in the Iceland Basin lead to the formation of weakly stratified Subpolar Mode Water. We explain why Subpolar Mode Water, the main water mass contributing to the westward flow, was denser at 57°N than at 59–62°N. At higher densities, both Intermediate Water and Icelandic Slope Water contributed more to the westward transport across the Reykjanes Ridge than the sum of Labrador Sea Water and Iceland-Scotland Overflow Water.