[en] The Siberian Traps represent one of the most voluminous continental flood basalt provinces on Earth. The mass extinction at the end of the Permian was the most severe in the history of life. In the present paper, these two major concurrent events that occurred are analysed and a geochemical model coupled with an energy balance model is used to calculate their environmental impact on atmospheric CO2, oceanic delta(13)C, and marine anoxia. The latitudinal temperature gradient is reduced relative to today, resulting in warmer temperatures at high latitudes. The warmer climate and the presence of fresh basaltic provinces increase the weatherability of the continental surfaces, resulting in an enhanced consumption of atmospheric CO2 through weathering. First, the eruption of the Siberian traps is accompanied by a massive volume of C-13 depleted CO2 degassed from the mantle and added to the ocean through silicate weathering, thus lowering marine delta(13)C. Second, the rapid collapse in productivity induces a strong decrease in the global organic carbon burial. This too tends to increase the proportion of light carbon in the ocean. These two effects can explain the low delta(13)C values across the PT boundary, and methane release need not be invoked to explain the delta(13)C fluctuations. It is proposed that the phosphorus cycle, which drives primary production in the model, plays an important role on the recovery of productivity and the delta(13)C variations. (c) 2005 Elsevier B.V All rights reserved.