Temporal variability and composition of settling particle fluxes on the Barcelona continental margin (Northwestern Mediterranean)

The results of a year-long sediment-trap experiment provide the first direct observations of sediment fluxes to the seafloor on the Barcelona continental margin. Time-series of vertical particle fluxes and major constituents (organic carbon, biogenic silica, calcium carbonate and aluminosilicates) were determined inside and in the vicinity of the Foix submarine canyon from May 1993 to April 1994. The spatial and temporal variability of bi-weekly total mass fluxes indicate significant high frequency variability related to physical and biological processes at this site. The Foix submarine canyon acts as an actual conduit for transport of sediment from the shelf to the slope, and as a mid-slope sedimentary depocenter. The shelf slope sediment transfer through this canyon is sporadic and takes place during and immediately after an important storm event or a river discharge increase. During periods of low cross-margin sediment transfer injected through the canyon, the vertical flux of particles is controlled by the along-slope geostrophic circulation. Breaking of the summer water stratification and vertical mixing also appears to be a major process which contributes to increasing the vertical flux of particles. Particle composition inside the Foix submarine canyon does not reflect any significant seasonal variations, but in the adjacent open slope, summer water stratification controls the composition of settling particulate matter. Retention of shelf-derived suspended particles along isopycnals in summer results in a decrease in total mass fluxes and an enrichment of organic carbon and clay mineral content in the settling particulate matter outside the canyon. During the spring biological bloom, the opal content increases particularly on the open slope, but the calcium carbonate does not because the high input of terrigeneous carbonate dominates that from biogenic carbonate production. The aluminosilicates fraction is the largest constituent of the vertical particle fluxes on the Barcelona continental margin, reaching higher percentages inside the Foix submarine canyon.