Interactions among Adriatic continental margin morphology, deep circulation and bedform patterns

Within the Mediterranean region, the Adriatic basin is one of the key sites for the formation and spreading of dense shelf water. Once formed in the northern shallow region as a response to strong, wintry cold air outbreaks, dense water masses move southeastwards as bottom-hugging gravity currents, eventually reaching the south Adriatic continental margin. A fraction of the dense water mass is thus intercepted by the shelf break, whence it flows down the continental slope driven by its negative buoyancy and interacting with ambient water and seafloor topography. This process generates a wide variety of dynamics and morphological features, such as erosional moats, furrows, giant comet marks, sediment drifts, and sediment waves. In this study we merge the outcomes of a state-of-the-art wave-ocean coupled numerical model with the geological evidence from the analysis of southern Adriatic bedform patterns. The model was run to reproduce an exceptional cold event that occurred in winter 2012, and benefits from a high-resolution bottom topography produced from data collected during recent bathymetric surveys. Model results allow the identification of flow pathways along and across the continental shelf and slope, with particular emphasis on the role of large-scale margin geometry in controlling morphodynamic processes and its implications in terms of resolution requirements for modelling purposes. Although modelled overall water fluxes and basin renewal ratios are mostly controlled by regional circulation and large-scale morphology, local topographic features and singularities appear crucial in triggering, concentrating and modulating bottom currents dynamics and sediment transport towards the South Adriatic Pit, as well as enhancing mixing and entrainment of ambient water. As long as this degree of information is provided within the bathymetric constraint, modelled hydrodynamic pathways in the study case are consistent with observed bedform morphology and their spatial pattern. For different zones in the continental slope, temporal variability of the flows has been investigated, permitting to disentangle the relative contribution of dense water cascading and background circulation at the basin and sub-basin scale in controlling bedform dynamics.This study gives a first quantitative insight on the hydrodynamic mechanisms responsible for South Adriatic Margin reshaping, suggesting a modelling approach to the interpretation of the high-resolution bathymetric and stratigraphic data made available by recent survey technologies.