Where do the Two Cores of the Irminger Current Come From? A Lagrangian Study Using a 1/10° Ocean Model Simulation

The Irminger Current (IC) brings relatively warm and saline waters northward in the North Atlantic subpolar gyre, contributing to the upper limb of the Atlantic Meridional Overturning Circulation. The IC is a two-core current with surface-intensified velocities. The eastern core, closest to the Reykjanes Ridge, is warmer and more saline than the western core. To investigate the source waters of the two IC cores, using a 1/10 degrees ocean model, we track Lagrangian particles released in the IC at OSNAP East (similar to 59.5 degrees N) in the upper 1,000 m backward in time for one model year. Over a 1-year time scale, nearly all particles are sourced from nearby regions of the Irminger Sea and Iceland Basin. Those seeded in the western IC core mostly originate from the Irminger Sea (83%), while those in its eastern core mostly originate from the Iceland Basin (69%). Iceland Basin water feeding the IC predominantly crosses the Reykjanes Ridge near 57 degrees N and 59 degrees N. Generally, particles from the Irminger Sea are colder and fresher than particles from the Iceland Basin. The fraction of waters from the Iceland Basin and the Irminger Sea varies from month to month. So, to explain monthly variations of the two IC cores at the OSNAP East line, changes in hydrographic properties in both basins as well as their contributions must be considered. Based on this model study, we interpret the Irminger Sea circulation as a basin-wide recirculation with an increasing contribution of Iceland Basin waters toward the ridge which is subject to monthly variations. The Irminger Current (IC) brings warm and saline waters northward along the western side of the Mid Atlantic Ridge. The IC is a two-core current where the eastern core is warmer and more saline than the western core. Here, we investigate the sources of the IC with a focus on the different water mass properties of the two cores to understand the observed transport variability of the IC. We release virtual particles in the IC in an ocean model simulation with a 1/10 degrees resolution and track their paths backward in time for 1 year. We find that the western core has its main source in the Irminger Sea with colder and fresher properties while the eastern core is mostly fed by warmer and more saline waters from the Iceland Basin. The mix of waters from the Iceland Basin and the Irminger Sea varies from month to month. So, to explain monthly variations of the two IC cores at the OSNAP East line, this model suggests that changes in hydrographic properties in both basins as well as their contributions must be considered. Both Irminger Current (IC) cores at 59.5 degrees N are fed by the Irminger Sea and Iceland Basin, with more Irminger water in the western core Iceland Basin water feeding the IC at that latitude predominantly crosses the Reykjanes Ridge near 57 degrees N and 59 degrees N The ratio of waters from the two basins varies on a monthly time scale which may lead to hydrographic and transport variability in the IC