Karst-dominated coastal systems and seafloor evolution: Insights into Quaternary shoreline dynamics and sedimentary processes in the Central Mediterranean Sea

Karst-dominated coastal systems represent highly dynamic environments where geomorphological evolution is tightly coupled with Quaternary sea-level fluctuations, sedimentary processes, and biogenic activity. The dissolution of carbonate bedrock through karstification causes the formation of complex seafloor morphologies, which not only reflect past environmental conditions but also apply significant control on present-day coastal dynamics. In such contexts, transgressive phases associated with Quaternary climatic cycles induce substantial shifts in shoreline positions, favoring the alternation of depositional and erosional regimes and shaping the stratigraphic and morphological architecture of submerged coastal platforms. These paleo-environmental settings have a lasting influence on modern coastal environments, as antecedent topography determines sediment accommodation space, hydrodynamic energy dissipation, and the spatial distribution of both soft and hard substrates. This, in turn, governs the establishment and persistence of key biogenic ecosystems such as Posidonia oceanica meadows and coralligenous assemblages. By reconstructing the paleo-environmental evolution of such systems, it becomes possible to better predict future shoreline behavior, assess coastal vulnerability, and guide conservation efforts aimed at preserving geomorphological and ecological heritage. This study addresses these themes by examining the seafloor offshore Marzamemi, a coastal sector of southeastern Sicily marked by intense karstic activity and high biogenic productivity. High-resolution backscatter Multibeam mapping and acoustic facies analysis reveal a complex mosaic of sedimentary environments shaped by the interplay of Quaternary sealevel variations, hydrodynamic forces, and biogenic processes. Three distinct paleo-lagoonal systems, located at depths of 􀀀 45 m, 􀀀 35 m, and 􀀀 20 m respectively, delineate former shoreline positions corresponding to past transgressive phases. These features are associated with variable sedimentary facies, ranging from fine sands in low-energy settings to coarser deposits shaped by tidal currents. High-resolution backscatter Multibeam mapping and acoustic facies analysis have provided new insights into the region's paleo-environmental evolution, geomorphological structures and sedimentary dynamics.