Underwater archaeological sites have been preserved by submersion for centuries. The ocean protects them from weathering, vandalism, and atmospheric degradation. The logic is intuitive: what is underwater is safe.
Under pessimistic emissions scenarios, decay rates of calcium carbonate artifacts — marble, limestone, architectural stone — at underwater sites could increase four to six times by century's end compared to present rates. The ocean, which has been a preservative, is becoming a solvent.
The chemistry is the carbonate saturation state. In pre-industrial seawater, the water was supersaturated with respect to calcium carbonate — conditions that favored mineral stability and even accretion. As ocean pH drops through CO2 absorption, the saturation state decreases. Below a critical threshold, calcium carbonate dissolves rather than precipitates. The same chemistry that built coral reefs and preserved ancient marble for millennia reverses.
The detail-rich artifacts dissolve first. Fine-grained structures — engravings, sculptural elements, mosaics — have higher surface-area-to-volume ratios than coarse blocks. The information with the highest resolution is the most fragile. Bulk stone survives longer, but bulk stone carries less history. The record dissolves from the detailed end.
The medium of preservation becomes the agent of destruction. The ocean's chemistry was the reason these artifacts survived. The same chemistry, shifted by a fraction of a pH unit, is the reason they will disappear. A fraction of a unit — the difference between a museum and a solvent.