In situ observations of density currents in a small submarine canyon in the eastern mediterranean

Submarine canyons are major conduits for density currents that transport water and sediment to the deep sea. To date, most in-situ studies and observations of these currents have been conducted in large submarine canyons that either incise the shelf, are adjacent to major perennial rivers, or a combination of both features. Little, if any, observational data exist from the more globally common small submarine canyons, that may be confined to the continental slope (headless) and located far offshore from smaller, ephemeral streams. In Israel- Eastern Mediterranean, submarine canyons are found only along the northern shore. These canyons are generally small (5–20 km long) and are not connected to major coastal rivers. Whether and how these canyons serve as pathways for density currents that transport sediment to the deep Levantine Basin was unknown. To address these questions, two moored stations (landers) equipped with instrument arrays were deployed at depths of 350 m and 710m along the thalweg of the “Bat-Galim” submarine canyon, offshore Haifa. The landers operated from October 2019 to June 2020 and from September 2020 to May 2021. In both deployments, winter density currents were recorded, characterized by turbid water moving rapidly down the canyon near the seabed, with velocities comparable to those reported in larger submarine canyons. During these events, sediment-laden warm and saline shelf water plunged beneath the colder, denser canyon water, leading to temperature inversions. This inversion may cause sediment lofting and upward convection through the water column once sediment settling relieves the otherwise buoyant warm water of its ballast. Mean sediment fluxes in the canyon during these deployments were extraordinarily high compared to both the adjacent shelf and the deep sea, suggesting substantial sediment transport. These results demonstrate that the Bat-Galim canyon, and likely other submarine canyons in northern Israel, serve as active pathways for annually occurring density flows. Additionally, the findings suggest a novel turbidity flow-driven mechanism for water column convection. These unique observations highlight the need for further investigation into the possibly significant role of small submarine canyons worldwide as key conduits for water and sediment transport to the deep sea, via density currents.