Modeling Continental Weathering Across the End-Permian Mass Extinction

The Earth experienced the loss of 80-90% of marine species and 70% of land species during the end-Permian mass extinction event (EPME) that occurred about 252 million years ago. The Siberian Traps (ST) volcanism is thought to have triggered the EPME through the release of large amount of carbon dioxide (CO2) into the atmosphere. Despite decades of research on the EPME, the exact impact of the ST volcanism on the EPME and the detailed patterns of the subsequent recovery of life are still hotly debated. Silicate weathering and organic carbon burial are thought to be responsible for sequestering CO2 from the atmosphere, but the relative roles of these processes remain unclear in driving the Earth’s system recovery from the CO2 emissions and global warming. We hypothesize that during the EPME and subsequent recovery, increased silicate weathering rate is not sufficient to lower the atmospheric CO2 levels and temperature remains high after the EPME. To test this hypothesis, we use lithium isotopes (delta7Li) as a proxy for changes in silicate weathering across the EPME. Fifty delta7Li data were obtained on shales from the Finnmark and Trøndelag Platforms in Norway that span the Permian-Triassic boundary (PTB). The results follow similar trend as those in the carbonate rich Meishan Section in South China published previously. The delta7Li data show an initial increase from 19‰ to 24‰ just before the PTB, followed by a decrease from 24‰ to 18‰ following the PTB. A dynamic lithium cycle box model suggests that the decreased delta7Li values suggest that weathering rates may have increased by 3 to 4 times during the PTB as a result of the elevated CO2 concentrations and temperature. However, continued outgassing from the ST may have exceeded the rate of carbon sequestration facilitated by silicate weathering, leading to long-term warming