Rapid Freshening of Iceland Scotland Overflow Water Driven by Entrainment of a Major Upper Ocean Salinity Anomaly

Newly available mooring observations from the Overturning in Subpolar North Atlantic Program (OSNAP) show an abrupt decline Iceland Scotland Overflow (ISOW) salinity 2017 to 2018 summer. Previous declines ISOW of similar magnitude have largely been attributed changes convectively formed deep waters Nordic Seas on decadal time scales. We that this rapid was driven by entrainment a major upper ocean anomaly Basin. This is shown tracking propagation into using combination and Argo observations, surface drifter trajectories, numerical model results. A 2-year total transit layer found. The results allows for modification ISOW, consequently lower limb Meridional Circulation, subdecadal timescales.