Sea level changes since the Middle Ages along the coast of the Adriatic Sea: The case of St. Nicholas Basilica, Bari, Southern Italy

During the last decade, several papers have been published to estimate the relative sea level change from coastal archaeological indicators of the last 3.4 ka BP in many locations of the Italian coasts and the Mediterranean Sea. The use of the archaeological information has been poorly focused for the Middle Ages, due to the few available coastal installations for this period, thus not allowing precise sea level estimation for the last 1000 years, to complement the instrumental data available for the last 100e120 years. This study discusses an archaeological marker of the Middle Ages, used to reconstruct the story of the sea level changes in the last 1000 years, at the St. Nicholas Basilica, built in 1087 AD along the coast of Bari (Apulia, southern Italy). The elevations of the ancient floor levels of the crypt underwent repeated flooding due to a continuous rising of the groundwater table, which required restoration and uplifting of pavements between 1087 and 1956 to keep them dry. The palaeo-sea levels have been obtained by measuring the position of the groundwater table, the elevation of which is mainly driven by sea level since the time of the construction of the Basilica. The elevation of the archaeological markers and the water table were compared against the latest predicted sea level curve for the Holocene along the coast of Bari. As this coastal area is unaffected by significant vertical tectonic motion over the last 125 ky, the data detail the timing of the relative sea level rise since the Middle Ages and can be used to improve the predicted sea level curve for this region for the last 1000 years.