Distribution and sources of organic matter in submarine canyons incising the Gulf of Palermo, Sicily: A multi-parameter investigation

Abstract

Submarine canyons act as conduits of terrigenous and marine organic carbon (OC) to deep-sea environments, although the contribution of each of these sources can largely vary depending on the canyon morphology and the prevailing sedimentary dynamics. The Gulf of Palermo is incised by several submarine canyons of similar dimension and depth range, but with slightly different morphosedimentary characteristics. Using a combination of geochemical parameters (OC, TN, δ13C, δ15N, and 114C), as well as biomarker signatures (proteins, carbohydrates, lipids, phytopigments, glycerol dialkyl glycerol tetraethers, and nalkyl lipids) and compound-specific δ13C analyses of surficial sediments, we assess the sources of OC deposited on the shelf and in three major submarine canyons (Arenella, Oreto and Eleuterio canyons). The aim is to provide further insights on the role of submarine canyons in transporting terrigenous OC across continental margins. According to a dual isotopic end-member mixing model with δ13C and 114C, the contribution of terrigenous OC was highest on the shelf (80 %) and decreased offshore, with contributions that ranged between 50 % to 70 % across the studied canyons. The dispersal mechanism of terrigenous OC and its specific sources differ among canyons primarily because of local differences of hydro- and sediment dynamics. Arenella Canyon, which is up-current and farthest from any river mouth, exhibited the relatively lowest terrigenous OC contributions (50 %), Oreto Canyon in the central part of the gulf had slightly higher contributions (50 %–70 %), and Eleuterio Canyon down-current and closest to shore had the highest proportion of terrigenous OC (60 %–70 %). Besides natural sediment dispersal mechanisms acting on this continental margin, continuous sediment resuspension by bottom trawling activities inside Oreto Canyon contributes to the down-canyon displacement of terrigenous OC, while promoting the ageing and degradation of OC in the canyon axis. Compound-specific δ13C analyses of fatty acids revealed that the sources of terrigenous OC differ across the studied submarine canyons, with Arenella and Oreto canyons receiving OC from a similar terrigenous source up-current from the gulf, whereas terrigenous OC deposited on the shelf and in Eleuterio Canyon originates from the Oreto and Eleuterio rivers that discharge into the Gulf of Palermo. This study provides further evidence that even non-river connected submarine canyons, such as Arenella, Oreto, and Eleuterio canyons in the Gulf of Palermo, are important sites of terrigenous OC sequestration and transfer to deep-sea environments, and that bottom trawling activities within submarine canyon environments can contribute to its resuspension and dispersal towards deeper regions.