Volcanic degassing necessary to produce a CaCO3 undersaturated ocean at the Triassic–Jurassic boundary

Carbon cycle model calculations have been conducted to test the idea that the entire ocean became undersaturated or nearly undersaturated with respect to calcium carbonate at the Triassic–Jurassic (T–J) boundary. A low degree of saturation at this time has been cited to explain the relative lack of carbonate sediments, especially those that originally contained the more soluble minerals, aragonite and highly magnesian calcite. Sensitivity analysis indicates that only extreme conditions of massive and short-lived degassing of CO2 and SO2 from CAMP volcanism could have led to an undersaturated ocean. With total degassing of 21,000 GtC as CO2 and 57,000 GtS as SO2, an undersaturated ocean with respect to all calcium carbonate minerals could have persisted for 20–40 ka, but only if the volcanic degassing lasted for no longer than 50–100 ka. With half this amount of total degassing over 100 ka a very low degree of supersaturation, possibly stabilizing only low magnesian calcite, could have been maintained for 20 ka.