The impact of cascading currents on the Bari Canyon System, SW-Adriatic Margin (Central Mediterranean)

The Bari Canyon System (BCS) is a peculiar erosional-depositional feature characterised by two main, almost parallel, conduits emanating from a broad crescent-shaped upper slope region. When viewed in cross sections parallel to the margin, BCS appears markedly asymmetric with a right hand (southern) side that is higher and steeper (about 800 m in relief and more than 30° steep). The left-hand side of the canyon is instead much smoother. As a consequence, bottom currents flowing along the slope from the north enter the canyon and interact with its complex topography leading to preferential deposition on the up-current side of preexisting morphological relief. Where mass-failure deposits generate morphologic relief, outside the canyon, sediment is preferentially deposited up current (N-ward). BCS includes three main EW-oriented sediment conduits: Canyon C, to the south, Channel B, in the central area, and Moat A in the north. Channel B shows a well developed levee deposit on its right-hand side and appears markedly straight and erosional on the upper slope. The deepest portion of Channel B is substantially abandoned and draped but still shows a subdued thickening of the draped unit north (and up current) of pre-existing morphologic relief, confirming the impact of along-slope flowing currents. Canyon C is flanked by erosional walls all the way to the basin floor where deep-sea furrows develop with a NW-SE orientation. Today, dense water formation in the Adriatic is seasonally modulated and displays a significant variability on inter-decadal scales. Dense water formation during glacial intervals was likely different from the modern because most of the North Adriatic shelf was subaerially exposed and the deep water mixing in the south was likely reduced, as suggested by paleoceanographic reconstructions. The growth patterns of BCS since the LGM are characterised by concurrent erosion of the upper portion of Channel B and of the lower portion of Canyon C. It is possible that flows through the straight, narrow and steep upper segment of channel B spill over its right hand levee in ca. 600 m water depth, where the relief of levee B on the channel floor is minimal, and enter Canyon C, where substantial erosion takes place. In this view, the upper portion of Canyon C, where hard grounds and corals are encountered, is flushed by currents characterised by reduced turbidity, while the lower part of Canyon C collects additional flows from upper channel B.