Acid rain responsible for mass extinction at T/J boundary

Today I read an advance online publication of van de Schootbrugge et al. in Nature Geoscience (doi:10.1038/ngeo577) on their interpretation of terrestrial mass extinction at the Triassic/Jurassic boundary. The role of wide spread volcanism at this time has been widedly acknowledged and its effect mainly attributed to CO2 emissions and consequent global warming. While this model explains the marine extinctions quite well, it does not fully explain the observed terrestrial extinction.

Van de Schoortbrugge et al. argue that their field observations suggest widespread acid rain and low sunlight caused by volcanic emmissions. They also point out the role of polycyclic aromatic hydrocarbons, which are toxic and are produced by heating organic compounds, e.g. coal seams.

Their findings strengthen the case that tectonics and resulting volcanism are major forcing mechanisms that trigger global mass extinctions. The parallels to the Permo-Triassic boundary are quite striking where some researchers suggest that the extrusion of the Siberian trap basalts throgh a major coal field would have also shown widespread ecological effects.