Rock Paintings of the Sierra de San Francisco

Impact of Microbiological Activity and Moisture on the Surface pH of Rock Art Sites: Cueva del Ratón, Baja California Sur, Mexico and Other Sites

Research at Cueva del Ratón, a UNESCO World Heritage Site in Mexico's Sierra de San Francisco, reveals that nitrate and sulfate concentrations significantly influence the surface pH of rock art, driven by moisture diffusion and microbiological activity. Atypical weather events, including rain and mist—uncommon in this arid region—triggered the formation of silica skins on some surfaces, a rare phenomenon in such environments. The study found that water availability, particularly through drip lines, enhances microbial metabolism (yeasts, molds, bacteria), leading to surface acidification that interacts with both the host rock and pigments. This process is exacerbated by climate change-induced weather shifts, such as increased hurricanes in Baja California. A novel, budget-friendly method using disposable test strips was employed to assess anion impacts on decay mechanisms, providing semi-quantitative insights into preservation challenges.