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

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

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]

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.

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

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?

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

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

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

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

Transient methane experiment ozone OH methane