Enhanced acidification of global coral reefs driven by regional biogeochemical feedbacks

Physical uptake of anthropogenic CO₂ is the dominant driver of ocean acidification (OA) in the open ocean. Due to expected decreases in calcification and increased dissolution of CaCO₃ framework, coral reefs are thought to be highly susceptible to OA. However, biogeochemical processes can influence the pCO₂ and pH of coastal ecosystems on diel and seasonal time scales, potentially modifying the long-term effects of increasing atmospheric CO₂. By compiling data from the literature and removing the effects of short-term variability, we show that the average pCO₂ of coral reefs throughout the globe has increased ~3.5-fold faster than in the open ocean over the past 20 years. This rapid increase in pCO₂ has the potential to enhance the acidification and predicted effects of OA on coral reef ecosystems. A simple model demonstrates that potential drivers of elevated pCO₂ include additional anthropogenic disturbances beyond increasing global atmospheric CO₂ such as enhanced nutrient and organic matter inputs.