Update on paleochemistry simulationsJean-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 [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 (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

H2S

OH

ozone

low emissions high 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

Production Surface flux

Loss rate (k OH)

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

Summary of our P/T work

Mass Extinction ofTerrestrial life

CO2 from VolcanicLarge Igneous Provinces

Large ReductionIn Atmospheric OH

Large Increasein Atmospheric CH4

Global Ocean AnoxiaMass Marine Extinction

Warm Stratified OceansInefficient Mixing

Collapse of Atmospheric OzoneIncrease in UV-B

Global warming (10oC)

CH4 Clathrate Release

Large H2S Emission

additional methane?

Impact on Atmospheric Chemistry

possible if large enough

methane

Transient methane experiment

ozone

OH

methane