Panagiotis Karsiotis

This study provides a comprehensive investigation of the sedimentary and tectonic evolution of Kalloni Gulf, a land-locked island embayment in the Northeast Aegean Sea. Information from a high-resolution seismic dataset was used to investigate the Late Quaternary seismic stratigraphy and internal structure of this shallow embayment. Four main seismic units were observed, bound by three key reflectors corresponding to main unconformities. The seismic units are related to periods of sea-level highstand and marine transgression, as well as to lowstand and marine regressions, dating back to the MIS 6 period. The chronostratigraphic framework of the observed units was based on previous work in the wider area and on global sea-level curves. In addition, information was gained regarding the hydrographic network of Kalloni Gulf, before the Holocene gulf flooding as well as during the Late Quaternary. The study also managed to identify faults and fault zones, which are distributed mainly along the southern and eastern margins of the gulf affecting both the gulf entrance physiography and the paleo-terrain of the eastern margin. With regard to specific structural features the fault zones are considered as strike-slip zones with an almost NNE-SSW orientation. These might be the submarine extension of the Aghia Paraskevi dextral strike-slip fault found onshore that dissects Lesvos, which is considered one of the main geohazards for the island. The results of the study are relevant not only for the reconstruction of the regional Quaternary geology, but also for broader research on Late Pleistocene-Holocene environmental change and tectonic-geodynamic processes in the wider northern Aegean Sea region.

Multibeam echosounders provide ideal data for the semi-automated seabed feature extraction and accurate morphometric measurements. In this study, bathymetric and raw backscatter data were initially used to manually delimit the reef morphologies found in an insular semi-enclosed gulf in the northern Aegean Sea (Gera Gulf, Lesvos Island, Greece). The complexity of this environment makes it an ideal area to “crash test” (test to the limit) and compare the results of the delineation methods. A large number of (more than 7000) small but prominent reefs were detected, which made manual mapping extremely time-consuming. Three semi-automated tools were also employed to map the reefs: the Benthic Terrain Modeler (BTM), Confined Morphologies Mapping (CoMMa), and eCognition Multiresolution Segmentation. BTM did not function properly with irregular reef footprints, but by modifying both the bathymetry and slope, the outcome was improved, producing accurate results that appeared to exceed the accuracy of manual mapping. CoMMa, a new GIS morphometric toolbox, was a “one-stop shop” that, besides generating satisfactory reef delineation results (i.e., detecting the same total reef area as the manual method), was also used to extract the morphometric characteristics of the polygons resulting from all the methods. Lastly, the Multiresolution Segmentation also gave satisfactory results with the highest precision. To compare the final maps with the distribution of the reefs, mapcurves were created to estimate the goodness-of-fit (GOF) with the Precision, Recall, and F1 Scores producing values higher than 0.78, suggesting a good detection accuracy for the semi-automated methods. The analysis reveals that the semi-automated methods provided more efficient results in comparison with the time-consuming manual mapping. Overall, for this case study, the modification of the bathymetry and slope enabled the results’ accuracy to be further enhanced. This study asserts that the use of semi-automated mapping is an effective method for delineating the geomorphometry of intricate relief and serves as a powerful tool for habitat mapping and decision-making.