Vertical and Lateral Structure of Arctic Subarctic Ocean Exchange via Nares Strait to the West of Greenland 2003 to 2009

Nares Strait separates northern Greenland and Ellesmere Island between 79.5 N and 82.5 N latitudes. It serves as a 40 km wide conduit of buoyant water and ice between the Arctic Ocean in the north and Baffin Bay in the south and supplies freshwater to the North-Atlantic. In 2003 we deployed a moored array to quantify volume and freshwater fluxes and to diagnose the dynamics responsible for these fluxes. The array was finally recovered in 2009. The subsurface instruments measured vertical profiles of ocean currents, temperature, and salinity as well as ice thickness across a section at 80.5 N latitude. We previously reported 3-year mean volume and (geostrophic) freshwater flux across this section as 0.72 +/- 0.11 Sv (10⁶ m³/s) and 20 +/- 4 mSv, respectively, for the 2003 to 2006 period. We here update these values for the 2007 to 2009 period and investigate vertical and lateral variability of ocean currents from tidal to interannual time scales. More than 90% of the kinetic energy in Nares Strait resides at tidal periodicities, which at our high northern latitude are generally above the inertial period when the lateral current shear (relative vorticity) is small. Analyzing 5-year long ocean current time series, we find deterministic vertical tidal velocity profiles that suggest 60-m thick boundary layers near both the bottom and the surface in water 300-m deep. Density stratification is stronger under the generally ice covered surface than near the bottom. We compare these observations with analytical model predictions of Prandle (1982) and find they agree well in the center of the channel, however, eddy viscosities are larger than expected, about 0.2 m²/s. Removing the tidal currents with a low-pass filter, we find similar vertical current profiles as the dominant mode from empirical orthogonal function analysis. We find enhanced variance at weekly and above-monthly time scales with largest amplitudes near 60-m and 140-m depth. Furthermore, similar to tidal variability the vertical shear is larger at locations near the center of Nares Strait than it is within 5 km off Ellesmere Island. We thus tentatively conclude that the geostrophic assumption away from vertical boundary layers breaks down adjacent to the coast. Prandle, D., 1982: Vertical structure of tidal currents and other oscillatory flows. Cont. Shelf Res., 2, 191-207.