Aragonite Saturation Horizon Shoaling

Aragonite saturation horizon shoaling is the upward migration of the depth where seawater becomes undersaturated with respect to aragonite (omega_ar equals 1), driven by anthropogenic CO2 uptake and ocean acidification. Above the horizon aragonite-shelled organisms such as pteropods and corals can calcify; below it their shells dissolve. Feely and colleagues found the Pacific aragonite and calcite horizons rising about 1 to 2 m per year, with total shoaling of 30 to 100 m in places since the pre-industrial era. The horizon is shallowest in the cold, high-CO2 North Pacific and Southern Ocean, where corrosive water now reaches the photic zone in upwelling regions.