Ocean Circulation Connecting Fram Strait to Glaciers off Northeast Greenland: Mean Flows, Topographic Rossby Waves, and Their Forcing

Abstract

AbstractFrom 2014 through 2016 we instrumented the ~80-km-wide Norske Trough near 78°N latitude that cuts across the 250-km-wide shelf from Fram Strait to the coast. Our measurements resolve a ~10-km-wide bottom-intensified jet that carries 0.27 ± 0.06 Sv (1 Sv ≡ 106 m3 s−1) of warm Atlantic water from Fram Strait toward the glaciers off northeast Greenland. Mean shoreward flows along the steep canyon walls reach 0.1 m s−1 about 50 m above the bottom in 400-m-deep water. The same bottom-intensified vertical structure emerges as the first dominant empirical orthogonal function that explains about 70%–80% of the variance at individual mooring locations. We interpret the current variability as remotely forced wave motions that arrive at our sensor array with periodicities longer than 6 days. Coherent motions with a period near 20 days emerge in our array as a dispersive topographic Rossby wave that propagates its energy along the sloping canyon toward the coast with a group speed of about 63 km day−1. Amplitudes of wave currents reach 0.1 m s−1 in the winter of 2015/16. The wave is likely generated by Ekman pumping over the shelfbreak where sea ice is always mobile. More than 40% of the along-slope ocean current variance near the bottom of the canyon correlates with vertical Ekman pumping velocities 180 km away. In contrast, the impact of local winds on the observed current fluctuations is negligible. Dynamics appear linear and Rossby wave motions merely modulate the mean flow.