Observations of turbidity currents in a small, slope-confined submarine canyon in the Eastern Mediterranean Sea

Abstract

Up to date, most in-situ studies and observations of turbidity currents were conducted in submarine canyons that are either, large, shelf incising or adjacent to big perennial rivers, or a combination of these features. Little if any observations have been made in the numerous, small submarine canyons (<20 km) that are confined to the continental slope and located far offshore smaller and often ephemeral streams, which are far more common globally. In this study, measurements were collected from October 2019 until June 2020 in Bat-Galim Canyon, a small (5 km long) submarine canyon located offshore Haifa, Israel, in the Eastern Levantine Basin (southeastern Mediterranean) where only minor, ephemeral streams reach the sea. This was performed using two similar mooring stations, positioned at depths of 350 and 710-meter along the canyon, which carried an array of measuring instruments, set between 2 and 50 meters above the canyon thalweg. Our data shows that the small Bat-Galim canyon is an active conduit for significant sediment transport to the deep-sea, much of it via turbidity currents that flow down the canyon during winter storms. The characteristic values of the turbidity currents in the Bat-Galim canyon were similar to those reported in much bigger submarine canyons. In addition, we observed temperature inversions during these events, wherein the sediment-laden warm surface water plunged and flowed underneath the colder, and otherwise denser, canyon water. This temperature inversion may lead to sediment lofting and upward convection through the water column for hundreds of meters, once sediment settling relieves the warm water of some of its ballast. These unique findings highlight the need to investigate the importance of small submarine canyons on continental slopes worldwide as water and sediment conduits to the deep-sea, even in dryer regions, and the impact of temperature inversions by turbidity currents on various water column processes.