Winter pulses of Pacific-origin water and resuspension events along the Canadian Beaufort slope revealed by a bottom-moored observatory

To assess hydrodynamics and particle transport variability at the Arctic shelf-basin boundary, a bottom-moored marine observatory was maintained from October 2003 to October 2006 over the ca. 300 m isobath on the slope of the Canadian Beaufort Sea (western Arctic Ocean). The mooring line was equipped at ~200 m depth with an oceanographic multi-sensors and a sequential sediment trap. Each winter, an abrupt and brief (<8 days) amplification of the subsurface eastward circulation was recorded when sea ice was covering most of the western Arctic Ocean. Compared to a mean background of 9 cm s^-1, the highest daily velocities recorded during the events reached 67, 94 and 62 cm s^-1, respectively in 2004, 2005 and 2006. The temperature-salinity signatures of the amplified flows displayed the signal of Pacific-origin shelf waters. The analysis of current components enabled us to propose that we detected the external limit of a submerged eddy formed via baroclinic instability of the shelfbreak current. We suggest that the periodic synchronicity of high atmospheric pressure along with rapid ice formation over the western Arctic Shelf were able to produce such instabilities in the jet. Each winter, the energy carried by the Pacific-origin water pulses was sufficient to erode the upper continental slope, producing marked sediment resuspension. Accordingly, the downward particle flux estimated with the sediment trap reached their annual peak values at the same time as the abrupt current surges were recorded. While the mean daily flux was ~0.1 g m^-2 d^-1 over the three-year period, the vertical mass flux reached ~0.8 g m^-2 d^-1 in both January 2004 and February 2006. In January 2005, however, the sediment trap clogged (>10 g m^-2 d^-1) as a result of the strong water pulse detected during this month. Our study stresses the importance of maintaining long-term marine observatories along the Ar- ctic shelfbreak to better elucidate the links between the changing atmosphere-sea ice-ocean system and biogeochemical fluxes in the Canadian Beaufort Sea.