Modeling the Consequences of the Siberian Traps

The impact of the Siberian Traps emplacement led to the extinction of 90% of marine species and 75% of terrestrial species. Due to the 3-5 Mkm³ of magma emitted over about 1Myr as determined by U-Pb dating. The extensive volcanic activity released massive quantities of gases into the atmosphere, particularly carbon dioxide (CO₂) and sulfur dioxide (SO₂). These emissions came from two main sources: magmatic emissions resulting directly from volcanic activity and thermogenic emissions produced by the intrusion of magmas into carbonate-rich, evaporite-rich, or organic matter-rich sediments within the Tunguska basin. The cumulative carbon emissions from the Siberian Traps are estimated to range between 21 000 and 105 600 Gt.

In the present study we considered the amplitude and timing from CO₂ and SO₂ degassing on the temperature, pH, δ¹³C and their implications for environmental perturbations during the Siberian Traps and the end-Permian mass extinction. We tested various scenarios and their consequences exploring the role of the volcanic sequence duration, mean size of lava flows, metamorphism and the biosphere.

We reconstructed the large igneous province (LIP) volcanic sequence in which we account for both magmatic and thermogenic emissions throughout the entire duration of the LIP emplacement. The SILLi 1.0 model (Iyer et al. 2018) was employed for the thermogenic emission. Parameters considered in the reconstructed sequence include, the duration of emplacement, the volume of lava flows and sills, the characteristics and age of the sediments intruded by sills, and the isotopic (δ¹³C) signature of sediments, organic matter and magma.

The environmental consequences of the reconstructed emission sequences were simulated using the biogeochemical model GEOCLIM. This model considers for both the short-term and long-term processes related to volatile emissions allowing for the calculation of changes in ocean temperature and pH, as well as disruptions in the carbon, oxygen, phosphorus, and alkalinity cycles.

We highlight the prevailing role of thermogenic gases to observe any significative changes in pCO₂, temperature, pH and HCO₃^2- δ¹³C these changes are specifically enhanced when coal bearing sediment are intruded. When intruded coal bearing sediment can cause the pCO₂ and HCO₃^2- δ¹³C to peak up to more than 100ppm and 0.4‰ respectively, over the span of a few centuries.

We demonstrate that the size distribution of flows has very limited impact on the long term tendencies but has a visible one on the short term and that the overall duration of the magmatic sequence has a significant effect. We also show that the collapse of primary productivity amplifies the environmental changes (3 Pal in PCO₂, 2°C in temperature and a decrease of more than 1.5‰ in HCO₃^2- δ¹³C) and that the combination of both volcanic processes (magmatic degassing and contact metamorphism degassing) and the biosphere are needed to partly explain the data.