Hydrodynamics and particle transport associated with a submarine canyon off Blanes (Spain), NW Mediterranean Sea

Particle transport rates were observed to be higher in a submarine canyon in the NW Mediterranean Sea than in areas surrounding the canyon. Velocity and particle profiles were used to reconstruct a three-dimensional (2-layer) grid of the flow field and resulting particle transport. Canyon topography enhanced both horizontal and downward transport of particles in an anticyclonic flow region over the canyon. Particles were probably not produced locally within the canyon but were transported from shallow coastal areas. Inorganic particles accounted for 75% of the particle mass with organic particles accounting for the remainder. The total particle mass had an uneven spatial distribution with higher concentrations in the canyon and along the coast near the head of the canyon. Generally, organic particulate production was negative (indicating biological respiration) and negligible, however, positive production rates did occur near the coast coincident with an area of high total particle mass. The respiratory losses of the organic material were lowest in the canyon, coincident with downwelling regions of high mass transport, thus biological degradation of organic material was expected to be slow. The downward transport of total particulate material leaving the upper layer of canyon was 5 x 10⁷ kg d^-1, of which 1.2 x 10⁷ kg d^-1 was organic material. The near shore and central part of the canyon probably act as traps for suspended particles by transporting them deeper in the canyon where higher residence times resulting from reduced advection may facilitate their sedimentation to the bottom.