The Environmental Impact of Siberian Traps Volcanism

New high-precision 40Ar/39Ar data confirm that the Siberian Traps extend as far west as the Ural Mountains, and from the Kuznetsk Basin in the south to the Taimyr Peninsula in the north; an area encompassing some 5 million km2. The bulk of this volcanism occurred at about 250 Ma (Ar-Ar time). These data, plus new and published Ar/Ar data from the P-Tr section at Meishan, China, confirm that volcanism and the mass extinction were synchronous. Here, we explore the causal link between volcanism and extinction. The volcanism is associated with global super-greenhouse conditions and widespread shallow oceanic anoxia - perhaps the sine qua non of the marine mass extinctions. Injection of isotopically 'light' carbon is required to explain the characteristic and dramatic negative carbon isotope excursion preserved in ocean water proxies, but because the CIE occurs after the mass extinction, this suggests that the carbon pulse (from breakdown of methane hydrates, or magmatic burning of coal or other hydrocarbons) was not the fundamental cause of the extinction. Rather, we suggest that magmatic CO2 released during the eruptions (complemented by pyrogenetic CO2 and methane) led to progressive CO2 accumulation in the atmosphere-ocean system (rates of long-term removal of carbon by geological processes are significantly lower than volcanic injection). Atmospheric accumulation may have been amplified by short-term sulphate-induced volcanic winters that caused collapse of photosynthetic cycles by atmospheric temperature fluctuations and sunlight attenuation, thus inhibiting carbon draw-down. Subsequent warming of the deep ocean may have triggered the methane pulse, leading to the main CIE. What lessons can we take away for present climate change? Unlike in the Cenozoic, when atmospheric CO2 progressively decreased to low pre-industrial levels, throughout the Permian atmospheric CO2 levels fluctuated strongly, and may have been as much as 10x present-day by the time that Siberian volcanism began. Arguably, the earth system was much more vulnerable to the additional carbon loading from volcanism. The environmental impact of flood basalt eruptions may thus be strongly influenced by the prevailing global climate conditions and atmosphere-ocean composition.