Global Projections of Coral Reef Sediment Dissolution in the 21st Century

Coral reefs build carbonate frameworks, but ocean acidification threatens to reverse this role by accelerating dissolution of permeable reef sediments. We combined Earth system model projections across five emission pathways with an aragonite saturation state-dissolution relationship to project global reef sediment dissolution through 2100. Under stringent mitigation, less than 2% of reef area experiences dissolution by 2100, compared with 30% under intermediate emissions and nearly all reefs under high emissions. Cumulative calcium carbonate loss reaches 2.5 gigatonnes under the highest-emission pathway, accompanied by 0.7 gigatonnes of potential carbon dioxide uptake that is globally negligible but signals framework degradation. Model-derived aragonite saturation states exceeded in situ observations in most regions, suggesting that reef sediment dissolution may begin earlier than gridded projections indicate. The southern Central Pacific emerges as a candidate acidification refugium warranting reef-scale evaluation. Continued high emissions could shift reefs from net carbonate accretion toward widespread structural loss.