The role of eddies on particle flux in the Canada Basin of the Arctic Ocean

Moorings with sequential sediment traps to study downward sediment flux in the Canada Basin of the Arctic Ocean were maintained in 3350 m of water year-round between September 1990 and July 1994. Sediment was collected nominally at 600-m depth and instruments measuring current, temperature, salinity and pressure were placed at several levels between 45 and 1515 m. Total dry weight particle fluxes were low (4.2, 2.1, and 8.2 g m −2 a −1 ) compared to those found in other world ocean basins. Particle flux varied greatly intra-annually. There were peaks during each summer, with differing seasonal timing and particle composition suggesting a correlation with inter-annual differences in summertime ice clearance. In winter, the particle flux was higher if the ice of the preceding summer was light. Enhanced primary production in summers with wider ice-free seas is a possible explanation, but inconsistent with the high lithogenic (LITH) content of most samples: A significant fraction of the particulate organic carbon (POC) content is refractory carbon. Another possibility is that the south-easterly wind pushing ice to the north-west in summers of reduced ice drives the Mackenzie River plume, laden with lithogenic sediment, behind it and out to the mooring site. There is also another factor in play: Peaks in particle flux frequently coincided with eddies, mesoscale circulation features with strongest current well below the surface. The highest measured flux occurred in the winter of 1994, synchronous with a baroclinic eddy which enveloped the mooring for 60 days while rotating cyclonically and moving slowly north-westward. Particles trapped at this time had high LITH and low POC contents, a relatively high molar ratio of biogenic silica to POC and appreciable chlorophyll a and phaeophytin pigments. Subsequent trap intervals coincided with the passage of a deeper anti-cyclonic eddy, also on a north-westward trajectory, which deposited material of different composition. These observations demonstrate that an understanding of the lateral transport of sediment by energetic physical phenomena is critical to the insightful interpretation of the particle flux measured with sediment traps at sites remote from the coast in the southern Canada Basin.