Eight years of continuous observations of the Deep Western Boundary Current from Cape Farewell

An important component of the deep limb of the Atlantic Meridional Overturning Circulation – the Deep Western Boundary Current (DWBC) – forms in the North Atlantic subpolar gyre from the combination of cold, dense water from the Nordic Seas and the ambient water within the gyre. Much of this water merges south of the Denmark Strait along the eastern flank of Greenland and flows southwestward toward the tip of Cape Farewell where the Overturning in the Subpolar North Atlantic Program (OSNAP) has continually monitored the DWBC since 2014 using moorings consisting of current meters, acoustic doppler current profilers, and temperature-salinity recorders. Previous estimates of the DWBC (σ_θ > 27.8 kg m^-3) at this location found 9-13 Sv of transport, including 10.8 Sv from the first two years of OSNAP data. This presentation extends the OSNAP estimates of the DWBC through 2022 and finds a 22% decrease in transport over the eight-year record from a thinning of the traditionally defined DWBC layer (σ_θ > 27.8 kg m^-3) and weakening velocities. This also results in a 27% decrease in transport of the densest water mass of the DWBC, Denmark Strait Overflow Water (σ_θ > 27.88 kg m^-3). Overall, the eight-year transport mean of the DWBC is 8.4 Sv. This presentation will also consider alternative methods for evaluating the DWBC that find a transport reduction of only 12-17% over the eight-year observation period.