Seasonal and spatial patterns in mass and organic matter sedimentation in the North Water

Sedimentation rates in the North Water between September 1997 and July 1999 were calculated from integrated monthly values for dry and organic matter, organic carbon, nitrogen, and sum-chloropigments, using pairs of multi-cup sediment traps moored at two depths >200 m at five stations. Highest fluxes in upper traps (144 and 297 g m−2 yr−1, 8 and 12 g C m−2 yr−1) occurred near Ellesmere Island at the western end of a cross-polynya transect (76°N). Rates to the east under the West Greenland Current (35 and 124 g m−2 yr−1, 4 and 7 g C m−2 yr−1) were higher than those in the central area of the polynya (13 and 39 g m−2 yr−1, 1.4 and 2.6 g C m−2 yr−1) and to the north at the entrance to Kane Basin (78°N), where levels of inorganic matter in settled material were relatively high (50 g m−2 yr−1, 1.8 g C m−2 yr−1). Minimum fluxes in upper traps (4.2 g m−2 yr−1, 0.7 g C m−2 yr−1) were measured at the southern limit of the polynya in northern Baffin Bay (75°N). Annual fluxes of particulate matter in the polynya between 1997 and 1999 (4–308 g m−2 yr−1, 1–14 g C m−2 yr−1) are higher than previously reported for ice-covered arctic regions. There was a similar seasonal progression at all locations with sedimentation rates increasing from winter minima during March followed by a larger secondary peak of maximum particle flux between June and September. Maximum sedimentation occurred earlier (April–June) on the eastern side of the polynya than off the coast of Ellesmere Island (July–September). High fluxes were sustained through late fall and early winter months at sites close to the coasts of both Greenland and Ellesmere Island. At most stations 40–50% of the annual organic matter sedimentation occurred during a prolonged period of high sedimentation between June and October. Sedimentation rates at 50 m above bottom were 30–50% higher than at shallower depths and settled material contained higher amounts of inorganic matter. Annual fluxes for all variables at four stations where between-year comparisons could be made showed that rates were two to five times higher in the second year of the study.