Impact of natural (waves and currents) and anthropogenic (trawl) resuspension on the export of particulate matter to the open ocean: Application to the Gulf of Lion (NW Mediterranean)

摘要: Abstract Modern sediment deposits on continental margins form a vast reservoir of particulate matter that is regularly affected by resuspension processes. Resuspension bottom trawling shelves with strong fishing activity can modify the scale natural disturbance waves and currents. Recent field data show impact trawls fine per unit surface comparable largest storms. We assessed both anthropogenic processes dispersal riverborne particles shelf sediments Gulf Lion shelf. performed realistic numerical simulations transport forced currents or fleet trawlers. Simulations were conducted for 16-month period (January 1998–April 1999) to characterise seasonal variability. The dynamics takes into account bed armoring, ripple geometry cohesive non-cohesive characteristics sediments. Essential but uncertain parameters (clay content, erosion fluxes critical shear stress sediment) set existing data. was controlled stress, whereas density distribution trawler fleet. Natural mostly occurred during short episodes, concentrated inner Trawling-induced resuspension, in contrast, throughout year outer total annual (5.6×106 t y−1, t metric tonnes) four orders magnitude lower than induced (35.3×109 t y−1). However net (erosion/deposition budget) (0.4×106 t y−1) only one order (9.2×106 t y−1). Off-shelf export concerned finest fraction (clays silts) took place primarily at southwestern end Gulf. favoured winter 1999 very intense episode dense water cascading. Export resuspended associated (8.5×106 t y−1). thought represent one-third suspended from A simulation combining reveals no significant changes rates compared sum each individual process, suggesting absence interference between