Particle transport in the Bari Canyon (southern Adriatic Sea)

Abstract

To define the sediment transport pathways along the southern Adriatic shelf and slope, two oceanographic cruises were carried out in the southern Adriatic, in July 2004 and in March–April 2005. To study the role of the Bari Canyon System on sediment dispersal, three moorings, including sediment traps and current meters, have been deployed near the bottom, at depths of ∼ 600 m, for one year (March 2004–March 2005). Two moorings were deployed within the canyon (station B in the northern branch and station C in the southern branch) and one on the adjacent open slope, north of the canyon system (station A). Total mass fluxes (TMFs) measured by sediment traps were always higher in the canyon than on the adjacent slope. The highest values were measured at station C (average 8.07 g m − 2 d − 1 ), roughly double those of station B (3.07 g m − 2 d − 1 ), and the lowest outside the canyon at station A (1.69 g m − 2 d − 1 ). The highest TMF were recorded in spring 2004, a period characterized by the lowest water temperatures and the highest current speeds (up to 72 cm − 1 ), which were associated with the highest across-slope current component, along the canyon axes. The simultaneous variations of fluxes occurring at the three stations imply that similar processes are active along the entire southern Adriatic margin, and that they are amplified inside the canyon. In spring a vein of southward flowing North Adriatic Dense Water (NAdDW) was observed along the Adriatic shelf. This was related to an enhanced across-slope current component, which was responsible for the higher particle fluxes, both on the open slope and at the canyon stations. These data suggest that the Bari Canyon is an efficient conduit for sediment from the Adriatic continental shelf to the deep basin. Downcore profiles of 210Pb in sediments collected below the traps have been used to estimate sediment mass accumulation rates (MARs) on a century scale. On the open slope, the annual trap flux recorded in 2004–2005 was lower than MAR. On the contrary, in the Bari Canyon, the annual trap flux was higher than MAR, indicating that the lateral advection of particles becomes predominant and that a fraction of the particles intercepted by sediment traps was only in transit through the canyon.