Modeling the atmospheric effects of the eruption of the Siberian Traps

The Siberian Traps are one of the largest known continental flood basalts, and have been invoked as a trigger for the catastrophic end-Permian mass extinction. The end-Permian pollen record has been interpreted as evidence that ozone depletion and mutagenesis may have played a role in the terrestrial mass extinction. Previous two-dimensional modeling has shown that degassing of halogens and organohalogens associated with eruption of the Siberian Traps may have been sufficient to catalyze the destruction of a significant fraction of the late Permian ozone layer. We use recent petrologic estimates of the degassing budget for the Siberian Traps as inputs to the National Center for Atmospheric Research Community Earth System Model 1.0 to explore the atmospheric effects of a range of individual volcanic eruption scenarios. Wet removal processes in the troposphere inhibit the transport of chlorine to the stratosphere. Methyl chloride and methyl bromide may be liberated during heating and metamorphism of Tunguska sedimentary rocks, possibly in conjunction with explosive pipe eruptions. Because they are relatively impervious to wet removal, even when methylated halogens are released at the surface they may reach the stratosphere and drive ozone destruction. The full duration of Siberian Traps volcanism probably spanned <1 Myr. Due to the complexity and computational cost of the model, and the likelihood of sporadic introduction of volatiles to the stratosphere, we focus on likely consequences of individual, much shorter eruptive episodes. A single pyroclastic eruption with sulfur and halogen emissions can produce strong radiative effects, which are mostly restricted to the northern hemisphere as a result of the high paleolatitude of the Siberian Traps. In addition, initial modeling results suggest that rapid eruption of twenty pipes with methylated halogen emissions could lead to a global ozone hole, with average decreases in ozone column density of seventy percent or more. We will explore further constraints on the types of eruptive episodes that could potentially have led to ozone depletion, ultraviolet poisoning, and the mutation spike reported in the pollen record.