Current surges and sediment erosion near the shelf edge in the Canadian Beaufort Sea: the role of wind and ice motion stress

Results from tautline moorings deployed near the shelf edge (~150 m isobath) in the Canadian Beaufort Sea over 2009-2015 provide evidence for the propagation of an eastward shelf-break jet carrying water of Pacific origin (or with similar properties) along the upper slope. Recurring episodes of elevated current velocities in the jet (up to ~60-80 cm s^-1) corresponded closely with sudden peaks in suspended sediments (up to >100 g m^-3) in the near-bottom boundary layer (<10 m) as derived from the acoustic backscatter of down-looking high-frequency acoustic Doppler current profilers. These events implied sediment erosion from a local source followed by rapid advection or redeposition, thus possibly contributing to the cycling of approximately 21-41 t m^-2 yr^-1 of sediments near the bottom at the shelf break. Current surges were driven by intensified wind and/or ice motion stress associated with anomalously high (upwelling-favorable) or low (downwelling-favorable) pressure systems. Both upwelling and downwelling storms were able to generate an intensification of the shelf-break jet (and its reversal during upwelling conditions), but the net vectorial displacement of suspended fluxes indicated that sediments were primarily transported to the northeast along the shelf toward the Canadian Archipelago. Based on sediment trap data collected over the lower slope, resuspended particles at the shelf-break may contribute to the offshore export of organic and inorganic matter only during downwelling-favorable conditions, primarily through eddy shedding from the shelf-break jet as a result of baroclinic instability. In addition to sediment erosion at the shelf-break, processes such as nearshore wave-driven resuspension forced by coastal storms and the cascading flow of dense winter water (both able to entrain material from the benthic boundary layer toward the shelf edge) are needed to explain the temporal variability of sinking fluxes over the lower slope.