1. Update on paleochemistry simulations Jean-François Lamarque and J.T. Kiehl Earth and Sun Systems Laboratory National Center for Atmospheric Research

2. Background Study of the chemical implications of large methane and hydrogen sulfide release at the P/T boundary on mass extinction Extension of the work by Kiehl et al. on the simulation of the climatic conditions at the P/T boundary

3. Modeling framework WACCM (85km, with 52 levels, 4x5) CH 4 -CO-NO x -HO x (-H 2 S-SO x ) chemistry (40-50 species); heterogeneous chemistry on stratospheric aerosols (no volcanic emissions) Use a slab ocean model to capture changes in sea-surface temperature Model is initialized from a fully-coupled model simulation by Kiehl and Shields [2005]

4. Simulation setup for methane Specify methane surface concentration boundary ranging from pre-industrial (700 ppbv) to 5000 times this value If all clathrate methane reaches the atmosphere over a short period, this would translate into 2700x.

5. Global average ozone With increasing methane, the total amount ozone starts collapsing around 750x UV-B increase

6. Methane lifetime Because of the water vapor feedback, there is always a significant amount of OH in the lower atmosphere and the methane lifetime stays relatively small Was there such a large release of methane over such a short period of time?

7. Hydrogen sulfide Hydrogen sulfide (H 2 S) is produced in the deep ocean and released amounts can dramatically increase under anoxic ocean conditions [Kump et al., 2005], as was the case at the P-T boundary. H 2 S chemistry can lead to ozone and OH destruction and sulfate formation 2 experiments: small (2 Tg(S)/yr) and large (5000 Tg(S)/yr) H 2 S flux

8. H2SH2S OH ozone low emissionshigh emissions The introduction of a large amount of hydrogen sulfide has the following effects Large decrease in tropospheric OH Large decrease in tropospheric ozone No significant impact on stratospheric ozone

9. Methane at steady-state At steady-state, the methane burden is given by The decrease in OH in the large H 2 S emission case translates into an twenty-fold increase of the steady-state methane concentration The amount of methane needed for an ozone collapse is twenty times smaller

10. Summary of our P/T work Mass Extinction of Terrestrial life CO 2 from Volcanic Large Igneous Provinces Large Reduction In Atmospheric OH Large Increase in Atmospheric CH 4 Global Ocean Anoxia Mass Marine Extinction Warm Stratified Oceans Inefficient Mixing Collapse of Atmospheric Ozone Increase in UV-B Global warming (10 o C) CH 4 Clathrate Release Large H 2 S Emission additional methane? Impact on Atmospheric Chemistry possible if large enough methane

11. Transient methane experiment ozone OH methane