Structure of the Bottom Boundary Current South of Iceland and Spreading of Deep Waters by Submesoscale Processes

The northeastern part of the North Atlantic subpolar gyre is a key passage for the Atlantic Meridional Overturning Circulation upper cell. To this day, the precise pathway and intensity of bottom currents in this area is not clear. In this study, we make use of regional high resolution numerical modeling to suggest that the main bottom current flowing south of Iceland originates from both the Faroe-Banks Channel and the Iceland-Faroe Ridge and then flows along the topographic slope. When flowing over the rough topography, this bottom current generates a 200 m large bottom mixed layer. We further demonstrate that many submesoscale structures are generated at the southernmost tip of the Icelandic shelf, which subsequently spread water masses in the Iceland Basin. These findings have major implication for the understanding of the water masses transport in the North Atlantic, and also for the distribution of benthic species along the Icelandic shelf. Water masses formed in the Arctic Ocean overflow into the North Atlantic at the bottom of the ocean, forming the so-called upper cell of the Atlantic Meridional Overturning Circulation (AMOC). The pathway of the currents carrying these water masses is still under debate due to a lack of observations. In this study, we discuss in details the pathway of these bottom currents in the specific area south of Iceland. We show that a steady current flows along the Icelandic continental shelf, and then divide in smaller structures when reaching the southernmost tip of Iceland. We also show that on its way, the current mixes the bottom layer of the ocean. These findings have major implication in the understanding of heat and carbon transport at depth in this area, which constitute an important response of the climate to anthropogenic forcing. An intense bottom boundary current originating from the Iceland-Faroe Ridge and the Faroe Bank Channel flows along the Icelandic Shelf The rough topography and the intensity of the current lead to bottom mixing and sustain a large bottom mixed layer Subsmesoscale structures generated locally participate in the spreading of deep water masses in the Iceland Basin