Linking Variable Nordic Seas Inflow to Upstream Circulation Anomalies

Helene Asbjørnsen1, Helen Johnson2 and Marius Årthun1, (1)Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway, (2)Department of Earth Sciences, University of Oxford, Oxford, United Kingdom
Abstract:
Volume transport variability at the Greenland-Scotland Ridge is known to be a major driver of heat content variability in the Nordic Seas. Consequently, variable transport at the ridge influences marine ecosystems and sea ice extent further downstream, as well as continental climate in north-western Europe. The predictability of the system depends on how variability in hydrography and volume transport at the ridge relate to large-scale ocean circulation changes in the North Atlantic. Here, we explore the link between transport variability at the Greenland-Scotland Ridge and upstream circulation anomalies in a Lagrangian framework. The 5-day mean output of an eddy-permitting ocean hindcast (ORCA025) is used together with the Lagrangian analysis tool ARIANE. Lagrangian particles are continuously released along a 2D-section at the ridge over a 30-year period (1986-2015) and tracked backwards in time for 10 years. Focusing on winter releases, 61% of the particles originate from the subtropical gyre (STG, south of 32ºN) while 8% of the particles originate from the subpolar gyre (SPG, north of 60ºN, west of 45ºW). There is, however, a more pronounced SPG pathway for particles initialized at the surface (27% SPG, 16% STG). Particles crossing the ridge during high inflow periods appear to have experienced a poleward shift of the North Atlantic Current compared to particles crossing the ridge during low inflow, and a higher proportion come from the STG (61% during high inflow, 29% during low inflow).