The effects of ocean acidification on stone deterioration were investigated both in the natural environment and in controlled laboratory conditions. Carbonate rocks selected as representative among the historical materials most frequently used in cultural heritage were characterized for their petrographic, chemical, and technical properties and then monitored for one year immersed in seawater. The field experimentation was performed along the coasts of Ischia in southern Italy, where seawater pH is locally affected by submarine CO2 seeps. The laboratory experimentation was conducted setting seawater pH, temperature, and pressure in a custom-made Microenvironment Simulator. A range of pH values encompassing pre-industrial, current, and projected future levels was considered for all investigations, supported by chemical analyses of seawater. The time evolution of the stone surfaces was monitored by measuring material loss from erosion due to mineral dissolution and textural changes, quantified on 3D models acquired at regular steps; additional investigations involved mass losses, calcite saturation indexes computed by geochemical modeling, and biofouling. By this approach, a correlation was established among stone properties, decay, and seawater chemistry.
On the other hand, the effects of extreme weather events were examined by simulations of storm-driven sea currents in a laboratory flume, monitoring the decay of the same rock types exposed to high-intensity water flows with suspended sediment. The multi-hour experiments were run with a combination of different flow velocities and sediment concentration and grain size. Material loss from erosion and surface textural changes were again quantified by 3D modeling, aided by microscopic observations, establishing a correlation among stone properties, erosion and characteristics of flow and seabed sediments.
Underwater stone deterioration was also investigated by observing its patterns in archaeological sites of the Mediterranean Sea (Anse des Laurons in France, Baia in Italy, and Amathus in Cyprus). A range of microscopic and morphometric techniques were applied for achieving a comprehensive petrographic, microchemical, topographic, and biological characterization of samples from an array of archaeological stone surfaces. This provided a perspective on the different marine environments, stone substrates and their mineralogical and textural properties, and how these influence the decay. An overview of the main chemical changes, the distribution and frequency of occurrence of the organisms involved in stone biofouling, and the morphological changes they cause was obtained.
These results were disseminated in international and national conferences (seven, to date) and on the official project website, and are being summarized in three full peer-reviewed articles. They are open to a series of possible exploitations: in academia, from a conservation and archaeometric approach or even addressing the ecological and geomorphological implications for the submarine environment; by heritage stakeholders, for fine tuning long-term strategies and policies for underwater site protection; in science communication, for further raising public awareness about the diverse impacts of climate change.
