Since the Industrial Revolution, the continuous exploitation of fossil fuels and the expansion of human-related activities have increased atmospheric carbon dioxide (CO2), accompanied by a concurrent rise in seawater CO2 partial pressure (pCO2). Much of the excess heat and CO2 is absorbed by the ocean, slowing down global warming1,2. However, the increasing concentration of CO2 is altering seawater chemistry, leading to a decline in ocean pH. Since pre-industrial times, the global mean surface ocean pH has already decreased by approximately 0.11 units3. Under the Shared Socioeconomic Pathway (SSP5-8.5), surface ocean pH is projected to further decline by up to ~ 0.37 units by the end of the 21st century4, reaching levels unprecedented over millions of years3,5. The Mediterranean Sea has been experiencing rapid climate changes with rates (e.g., mean temperature, heat wave frequency, sea level rise) exceeding global trends6. It has been estimated a decline of 0.018–0.028 pH units per decade that combined with increasing temperatures, enhanced stratification, heatwaves, sea level rise, and alterations in productivity, among others, poses a serious threat to this basin6. The western Mediterranean Sea (e.g., Alboran Sea, Strait of Sicily, Northwestern Mediterranean) has recorded an exacerbated decrease in pH, as supported by boron isotopes and...