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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) • CH4-CO-NOx-HOx(-H2S-SOx) 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 
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.
UV-B increase Global average ozone With increasing methane, the total amount ozone starts collapsing around 750x
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 (H2S) 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. • H2S chemistry can lead to ozone and OH destruction and sulfate formation • 2 experiments: small (2 Tg(S)/yr) and large (5000 Tg(S)/yr) H2S flux
low emissions high emissions H2S OH ozone • 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
The decrease in OH in the large H2S 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 Methane at steady-state At steady-state, the methane burden is given by
CO2 from Volcanic Large Igneous Provinces additional methane? Global warming (10oC) Warm Stratified Oceans Inefficient Mixing Global Ocean Anoxia Mass Marine Extinction CH4 Clathrate Release Large Increase in Atmospheric CH4 Large H2S Emission Impact on Atmospheric Chemistry Large Reduction In Atmospheric OH Collapse of Atmospheric Ozone Increase in UV-B possible if large enough methane MassExtinction of Terrestrial life Summary of our P/T work
Transient methane experiment ozone OH methane