Title: A decade of East Reykjanes Ridge Current observations: velocity structure, transport variability, and dynamics

Name: Dr. Tiago Carrilho Bilo, University of Maine

Abstract: The cyclonic horizontal circulation of the subpolar North Atlantic acts as an important conduit of the Atlantic Meridional Overturning Circulation (AMOC) due to the progressive watermass transformation along the complex subpolar boundary current system. Flowing south-southwestward along the eastern flank of the Mid Atlantic Ridge in the Iceland Basin, the East Reykjanes Ridge Current (ERRC) is a key link in this subpolar AMOC pathway by carrying modified subtropical waters and deeper Icelandic Slope Water before retroflecting towards the Irminger Sea. We use approximately 10 years of continuous moored velocity and hydrographic measurements, complemented by quasi-synoptic CTD and LADCP profiles collected between 2014 and 2024, to show that the ERRC is a ~100 km-wide jet that extends from the surface to around 1500 m depth, characterized by velocity maxima near the surface and the bottom. Notably, while the flow exhibits significant variability across timescales from weeks to a few years, with short-lived transport anomalies exceeding 10 Sv, its meandering activity seems limited. As a result, the ERRC jet rarely meanders beyond the fixed area we identified as the ERRC domain. We find that the ERRC transport is on average ~7.9 Sv and its variability is dominated by quasi-annual barotropic-equivalent oscillations, which we think is linked to the barotropic adjustment of the Subpolar Gyre to winds. While total transport variability does not present significant seasonality, we observe significant baroclinic vertical shear anomalies dominated by the seasonal cycle. These anomalies result in velocity anomalies that differ in sign near the surface and the bottom, minimizing the impact on the vertically integrated ERRC transport.