Spatial and temporal variability of particle flux at the NW European continental margin

A synopsis of results from two sediment trap moorings deployed at the mid- and outer slope (water depths 1450 and 3660 m, respectively) of the Goban S pur (N.E. Atlantic Margin) is presented. Fluxes increase with trap deployme nt depth; below 1000 m resuspended and advected material contributes increa singly to bulk flux. Fluxes of dry weight, POC and diatoms in the traps 400 m above bottom (mab) are smaller than those recorded at the sediment surfa ce due to lateral fluxes in the benthic nepheloid layer. These near-bottom fluxes are larger at shallower water depths. Pa-231/Th-230 ratios in sedime nting material suggest that boundary scavenging is not significant at the G oban Spur. Fluxes of Pb-210 in the intermediate and deep traps are comparab le to the Pb-210 supply rate at this site. At the outer slope, sediment Pb- 210 fluxes are similar to those measured in the traps 400 mab; at the mid-s lope they are a factor of 2 higher, once again indicating large near-bottom lateral particle input. Based on POC-normalised biomarkers in sedimenting material, we followed changes in the quality of sedimenting material with d iffering trap depth and on seasonal and event-related time scales. In sprin g fresh, diatom-dominated sedimentation occurs, with progressive degradatio n of POC with time (to winter) and depth (from 600 to 3220 m). Deeper traps are distinguished on the basis of opal and aluminium fluxes that are domin ant in lateral input. A storm event during late September 1993 was clearly reflected in the delta N-15 isotope ratio of sedimenting material, with a t ime lag of 2-3 weeks. Diatom and opal fluxes were elevated in this storm-re lated signal, and its biomarker composition in the 600-m trap was similar t o that during spring. An estimate made of upward nitrate flux (new producti on) at the shelf break and at the outer slope indicated a 2-fold higher new (export) production at the shelf break. Particulate organic carbon export from the shelf break to below the depth of maximal seasonal mixing ranges b etween 3 and 9% of primary production. (C) 2001 Elsevier Science Ltd. All r ights reserved.