Geological Controls on Dipping and Submerged Marine Notches in Two Coastal Caves of Northwestern Sicily (Central Mediterranean Sea) and Their Significance as Relative Sea-Level Indicators

Marine tidal notches (MTNs) are widely recognized as reliable indicators of mean sea level and have been extensively used along carbonate coasts of the Mediterranean Sea, where tidal ranges are generally small, to reconstruct relative sea-level changes. MTNs develop primarily through the combined effects of carbonate dissolution associated with the interaction between marine and meteoric waters, bioerosion by intertidal organisms, and mechanical removal of weathered material by wave action. Previous studies have demonstrated that notch morphology reflects a combination of tidal range, lithology, and cliff-toe depth, while significant freshwater discharge may enhance notch development. In microtidal Mediterranean settings, the morphology and elevation of MTNs are therefore closely related to local sea-level conditions. Detailed surveys of MTNs throughout the Mediterranean have documented both typical tidal notches and anomalous morphologies. Among the latter, notches developed within ria-type coastal settings may progressively deepen from exposed to increasingly sheltered environments, producing landforms referred to as dipping marine notches (DMNs). Here, we investigated two sea caves in northwestern Sicily (central Mediterranean Sea), where contrasting notch shapes are preserved. At Capo Zafferano Cave, a present-day tidal notch progressively transforms into a dipping marine notch within less than 20 m of the cave entrance, whereas at Cala Rossa Cave a submerged notch remains closely associated with the corrected sea level, with repeated measurements ranging from 0.00 to −0.10 m. We evaluate the possible role of freshwater spring discharge in its formation and preservation. High-resolution geomorphological measurements were collected during repeated field surveys and corrected for short-term tidal variability using the Palermo tide-gauge record. The repeated measurements were quantitatively assessed using statistical analyses accounting for the repeated-measures structure of the dataset. Water-temperature measurements at Cala Rossa revealed a marked thermal anomaly, with temperatures reaching 25.0 °C in the freshwater-influenced inner sector compared with 28.8 °C at the cave entrance, consistent with the presence of a distinct freshwater-influenced water mass within the cave. Ecological and biological information were presented as a description of the study sites, providing a biotic context for the observed tidal notches. The results provided quantitative evidence for the reproducibility of the observed notch positions under different tidal conditions and support the interpretation of contrasting notch shapes as the result of different hydrodynamic and geomorphological processes. These findings highlight the importance of freshwater discharge, cave confinement, and local hydrodynamic conditions in controlling the development and preservation of tidal and submerged notches in Mediterranean carbonate coastal environments.