Tidal notches in Mediterranean Sea: a comprehensive analysis

Recent works state that the modern tidal notch is disappearing worldwide due to sea level rise in the last century. In order to assess this view, we measured the largest possible number of sites where the modern tidal notch is present around sea level. We carried out our work in the Mediterranean sea, which has narrow tidal ranges and low-intensity sea storms if compared to other seas, and where the study of tidal notches has been extensively reported in literature. We surveyed 73 coastal sites in Italy, France, Croatia, Montenegro, Greece, Malta and Spain, and we report observations made on tidal notches worldwide. At each site, we measured notch width and depth, the characteristics of the biological rim at the base of the notch, and we correlated these parameters with wave energy, tide gauge data and rock lithology. The results of observations and measurements shed a new light on: i) the accurate elevation of mean sea level with respect of the notch position; ii) the correlation between morphometric features and meteomarine processes; iii) the mechanisms that influence the genesis and evolution of tidal notches, including those derived from: chemical (mixing-corrosion), biological (erosion by intertidal organisms), mechanical (meteomarine), vertical tectonics, and climatic processes. Our data show that in tectonically stable areas the current tidal notch is always present, apart from rare exceptions (2/73 sites) related to local limiting factors. Our results suggest that notches are not disappearing worldwide, but modern notches are the result of complex interactions between a series of factors affecting their formation. This leads to new interpretations on the genesis and evolution of tidal notches and restates their importance as sea level indicators