Composition and variability of downward particulate matter fluxes in the Palamós submarine canyon (NW Mediterranean)

Abstract

To study the temporal and spatial variability of downward particle fluxes in the Palamós submarine canyon, seven sediment traps were moored inside and in the vicinity of the canyon from March to November 2001. Total mass fluxes, major constituent (organic carbon, opal, calcium carbonate and lithogenics) contents and fluxes, and 210Pb activity of particulate matter were obtained from two consecutive deployments at intervals of 10 and 12 days, respectively. Downward particle fluxes measured at the Palamós canyon head were 2 to 9 times higher than those measured in other northwestern Mediterranean canyons, and this relation increased drastically at 1200 m depth, where observed particle fluxes were 1 to 2 orders of magnitude higher than those reported in other surrounding canyons at similar depths. The highest near-bottom downward particle fluxes were not recorded in the canyon head but in the mid-canyon axis during late spring/summer, as a result of sediment gravity flows triggered by trawling activities at the canyon rims. In comparison to the adjacent open slope, Palamós Canyon is a prime site for the focusing and across-margin transference of total and organic matter. Off-shelf sediment transport was enhanced during a severe storm in November 2001, when a sharp increase in downward particulate fluxes was observed in the whole canyon both near the bottom and at intermediate waters. Despite the dominance of lithogenic particles all year round, a siliceous bloom affected the whole study area in March–April. An asymmetrical pattern was observed between the north and south canyon walls, with higher mean downward fluxes in the latter case, a fact related to the flow regime inside the canyon. The spatial–temporal distribution of total mass fluxes and major constituents defined two domains in the Palamós Canyon: an “inner” domain (up to 1200 m depth) constricted by the canyon topography and mainly influenced by a lateral transport of particles resuspended from the adjoining shelf and upper slope, and an “outer” domain, where slope dynamics and seasonal trends are more important in determining the composition and amount of downward particulate fluxes.