A 10-m vertical displacement on the Romanian Black Sea coast during modern history

Sea level reconstructions in the Black Sea basin and elsewhere rely on the identification of sea level markers and on the understanding of their post-genetic vertical movements. We present here evidence of a fast, bi-directional vertical displacement on the western Black Sea shore at Mangalia, Romania. We argue that an area situated near the shoreline was submerged 4 m, subsequently filled with marine silts and sands, then uplifted by 10 m, where it currently stands. Radiocarbon dating of several types of materials from the infill, as well as archaeological evidence, indicate that this displacement occurred during the eighteenth to nineteenth centuries. Mollusc shells found in anatomical connection close to the top of the sediment sequence have a 14C reservoir age offset of ~ 900 years, probably due to the hard water effect. This is much larger than the ~ 400 year offset that is generally considered for the Black Sea and highlights the problematic dating of Black Sea coastal sediments. The findings of this study offer strong evidence of short-term, local tectonic movements that should be considered when past sea levels are calculated, while at the same time serve a warning for urban and marine development planners.