Coral reefs will transition to net dissolving before end of century.

Ocean acidification refers to the lowering of the ocean's pH due to the uptake of anthropogenic CO from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calcium carbonate (CaCO) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (Ω) of overlying seawater and that CaCO sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater Ω reaches 2.92 ± 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution.