Stone deterioration at underwater archaeological sites in the Mediterranean Sea

The Mediterranean Sea hosts a remarkable underwater cultural heritage that reflects millennia of interaction between people and the sea, preserving evidence of ancient societies, their maritime trades, travels, economies, coastal lifestyles, and technological achievements. Its protection and preservation rely on knowledge of the properties and deterioration of historical materials and their interaction with the marine environment. This study addresses the state of conservation, decay, and vulnerability of stone structures and artifacts from underwater archaeological sites across the western, central, and eastern Mediterranean Sea: the Roman harbor of Anse des Laurons in France, the Roman residential complex of Baia in Italy, and the Hellenistic harbor of Amathus in Cyprus. Petrographic, textural, chemical, and biological-morphological investigations of archaeological stone were carried out by microscopic and microchemical techniques, along with a novel application of 3D surface modeling. These allowed identifying the materials used for structural and ornamental purposes, their biofouling, and related changes in stone surface texture and chemistry. Biodeterioration is the dominant decay form, affecting composition, aesthetics, and legibility of artifacts. The decay patterns are influenced by the diverse characteristics of historical materials and the marine environmental and archaeological context, but appear relatively uniform across the Mediterranean basin. The findings overall contribute to advancing the understanding of the risks to underwater cultural heritage and can support the development of improved conservation methods, technologies, products, and protection policies, also in light of climate change and its effects on marine biodiversity and environments.