BIOSPHERE RESPONSE TO VOLCANIC CO2 RELEASE: SIBERIAN TRAPS AND END-PERMIAN MASS EXTINCTION

The response of the biosphere (ocean/atmosphere/biota) to volcanic injection of carbon dioxide undoubtedly depends on the rate and total amount of carbon added. This in turns depends on the CO₂ content of the degassing magma and the type of crustal materials with which it interacts. For example, estimates of CO₂ emission during the emplacement of the Siberian Traps, coincident with the major phase of end-Permian mass extinction, range as high as 100,000 Pg CO₂. While this indeed is a considerable quantity of carbon, its impact on the biosphere depends on the duration of eruption. At present-day rates of volcanism (approximately 250 Tg CO₂ per year), volcanoes emit this amount of CO₂ in approximately 400,000 years. Thus, to substantially perturb the carbon cycle, atmospheric pCO₂, climate, the acidity of the ocean and its redox state, the release of CO₂ has to be over a considerably shorter interval.

Here we use an Earth system model of intermediate complexity, Genie-1, to quantitatively evaluate the marine biospheric response to a range of CO₂ injection rates and total quantities that spans those proposed for the end-Permian event. We explore the sensitivity of this result to the assumed initial state of the biosphere: greenhouse vs. icehouse, to address the question of how important it was that the Late Permian was already a warm period in Earth history, high atmospheric O₂ vs. low, and sluggish vs. intense ocean circulation, because of uncertainties in these states. We also determine the effect that a putative lack of seafloor carbonate buffer has on the system response for this time (and all previous times) before planktonic carbonate producers had evolved. From these experiments we establish critical threshold CO₂ release rates and durations that are capable of causing environmental disturbances capable of mass extinction.