Along-stream and temporal variability in the boundary currents east and west of Cape Farewell, Greenland

At Cape Farewell, the narrow southwest flowing East Greenland Boundary Current System turns northwest to become the West Greenland Current System. Previous studies show that the West Greenland Current System provides important source waters to the interior of the Labrador Sea that are ultimately transformed into Labrador Sea Water. Direct-velocity measurements, especially in the winter months, have been sparse. Our knowledge of the continuity between the East and West Greenland Currents Systems is still limited. On longer time scales, it is still unclear how the West and East Greenland Current Systems’ strength and transport respond to interannual variability. This study makes use of an acoustic Doppler current profiler (ADCP) mounted on the hull of the container ship Nuka Arctica to measure upper ocean currents around southern Greenland. Twice every three weeks the ship rounds Cape Farewell and travels the west Greenland coast to Nuuk. Two time periods are considered: 1999-2002 and 2012-2016. Here, velocity structure and transport within the upper 400 meters depth are compared at six sections across the current systems, two along the south-eastern side of Greenland and four along the west side of Greenland. Transport in the West Greenland Current System is found to be up to 1.6 Sv lower in the East Greenland Current System, indicating deflection by Eirik Ridge. Winter transport is generally higher than summer with a more pronounced difference in the east. The West Greenland Current System shows no measurable response 6-18 months following a short-term negative wintertime NAO while a negative NAO phase leads to a lower transport in the East Greenland Current System.