Particle fluxes and biogeochemical processes in an area influenced by seasonal retreat of the ice margin (northwestern Ross Sea, Antarctica)

Fluxes of biogenic components were determined using time-series sediment tr ap samples collected at site B (74 degrees 01.50'S, 175 degrees 05.55'E) in the northern Joides Basin of the Ross Sea from December 1994 to January 19 96. In most cases, a great part of the material collected by traps (200 and 540 m depth) was biogenic, opal being the most abundant constituent follow ed by organic matter. The composition of particles shows a seasonal pattern in the upper trap, which is much less evident at depth. Fluxes showed a ma rked seasonality due to the presence, in winter, of ice cover. During the s ampling period, mass fluxes varied from 0.03 to 120 mg m(-2) day(-1) and fr om 24 to 393 mg m(-2) day(-1) at the upper and bottom level, respectively. Values of 0-64 mg m(-2) day(-1) of biogenic silica and 0-7.8 mg m(-2) day(- 1) of organic carbon were obtained at 200 m depth. Near-bottom fluxes were almost always much higher: 11-141 and 1.5-19 mg m(-2) day(-1), respectively . Pb-210 fluxes are lower than expected, and this means that particles sink rapidly without reaching an equilibrium with the radiotracer. A mechanism of focusing affects the bottom trap and much more, the seafloor. At site B, we measured particle fluxes that are much lower than those obtained at oth er locations in the Ross Sea. This can be due to low production and export during the sampling period, and underlies the necessity to further investig ate the interannual variability of these processes. (C) 2000 Elsevier Scien ce B.V. All rights reserved.