concept

Ocean acidification

The shift in seawater chemistry as the ocean absorbs surplus CO₂ from the atmosphere. Dissolved CO₂ forms carbonic acid, releasing protons that lower pH and simultaneously consuming carbonate ions — the very building block corals need to secrete limestone. The consequence is tracked by the aragonite saturation state (Ω): the lower Ω falls, the more energy calcification costs, and below a critical threshold (roughly 3.0–3.3) bare framework begins to dissolve rather than grow. It is the quiet threat to a reef's foundation: no fire or bomb required — the ground can come apart simply because the water changed its chemistry.