Coccolithophorids on the continental slope of the Bay of Biscay―production, transport and contribution to mass fluxes

International audienceCoccoliths collected by sediment traps deployed on the slope of the Bay of Biscay (northeasternAtlantic), from June 1990 to August 1991, were examined to determine their contributionto the transport of carbonate on a mid-latitude continental margin. They also were used astracers of particle transfer processes on this slope. Two traps located at 1900 m, respectively at2300 (Mooring Site 1) and 3000 m (Mooring Site 2) water depths provided high-resolution(4}7 days) time-series samples covering a 14-month period at MS2 and a 3-month period atMS1. Coccoliths from 28 species were identi"ed over the course of the experiment, amongwhich Emiliania huxleyi was always dominant (relative abundance range: 59}93%). Totalcoccoliths number #uxes were high but variable, ranging from 390]106 to 1610]106 coccolithsm~2 day~1 at MS1, and from 58]106 to 1500]106 coccoliths m~2 day~1 at MS2. Thetime-weighted mean #ux, calculated for the whole experiment at MS2, was 499]106 coccolithsm~2 day~1. Estimate of coccoliths minimal contribution to total carbonate #ux at 1900 mdepth averaged 12%, which represented a weighted mean #ux of 7.3 mg m~2 day~1(2.7 g m~2 yr~1). Lateral transport of coccoliths resuspended from shelf and/or upper slopesediments seems to be the dominant transfer process to depth on this northeastern Atlanticslope. Nevertheless, the clear seasonal succession observed in the species composition impliesthat the deposition/resuspension/transport sequence is rapid (presumably less than a fewmonths). Several short and unsmoothed signals directly issued from coccoliths bloom eventsalso were recorded in our traps, a result that indicates rapid settling rates. The overall coccolithsedimentation processes appear as being quite diversi"ed, but quantitative and qualitativeanalyses of aggregates collected by the traps suggest that they are important carriers ofcoccoliths in this margin environment