Paleocene-Eocene Thermal Maximum

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The PETM Event


What Triggered the PETM?







How did the Earth System Recover from the Carbon Injection?

Current theory predicts two main responses to the carbon injection and ocean acidification at the PETM.

Carbonate Ion Recovery

The first predicted response is that carbonate compensation should return the saturation state (carbonate ion concentration) of the ocean back to pre-PETM levels over the course of about 10,000 years.

Launch the carbon model and apply an instantaneous carbon input of 4000 Gt C of thermogenic methane. Then alter the run duration to 20,000 years and run the model. Look at the resulting output plot for carbonate ion in the deep box and observe how the value of the variable in the model converges back towards the starting (pre-PETM) value. On the main window for the model, click on 'Save Simulation' and then import the saved data file into an analysis package such as Excel. Use this saved data to calculate the "e-folding response time" for the carbonate ion recovery. Using the saved data again, calculate the time that it takes for the deep box carbonate ion concentration to recover 90% of the way back towards its equilibrium value.

How does this predicted speed of recovery compare to the time that it takes for CaCO3 MAR (mass accumulation rates) and lysocline depth to recover in the South Atlantic (Zachos et al., 2005)?

Left-Over CO2 and Global Warming

A second aspect of the predicted response is that any injection of CO2 should leave behind a long-lasting (hundreds of thousands of years) residual of elevated CO2 and global warming. This is described for the present-day and fossil fuels on the page describing the long-term legacy of elevated CO2.

Run the carbon model as above, but with a run duration of 50,000 years (this will take some time to complete). Compare the trajectories of carbonate ion and of atmospheric CO2. By the time that carbonate ion has returned 90% of the way back towards its initial value, how close is atmospheric CO2 to its initial value? After 50,000 years how close are they both?

How does the model prediction of prolonged atmospheric CO2 and global warming compare to data, if δ18O is assumed to be a reliable indicator of surface ocean (and therefore Earth surface) temperature?


The exercises above give an introduction to some of the main questions that paleo researchers are targetting at the present time. The carbon model you have just used is not ideal for simulating the PETM, however, in the sense that it has no horizontal resolution and hence cannot reproduce geographical changes, whereas the data suggest that ocean circulation patterns changed during the PETM excursion and that this affected the palaeo records (Nunes & Norris, 2006; Zeebe & Zachos, 2007). For this same reason (changes in circulation affecting local records), we do not yet have a global picture of how the planet changed at the PETM. For instance, we only have detailed knowledge of the change in lysocline depth at one site, in the South Atlantic, but data at other sites suggests that the lysocline changes were not uniform across the globe (Zeebe & Zachos, 2007). Much remains to be done in terms of building a more complete global picture of how the Earth changed at the PETM, but collection of more data and close comparison to model results will eventually give us the answer.

External links

Further Reading