Investigating transient weakening of Earth’s silicate weathering ‘thermostat’ as a possible driver of climate perturbations in the geological past: A middle Eocene case study

• Applicant: Dr. Patrick Frings, since 10/2023
• Subject Area: Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459347757

The silicate weathering feedback keeps our planet habitable by drawing down the CO2 released by volcanism and moderating global climate. However, in the past the capacity of Earth’s surface to react with CO2 – its “weatherability” – was not constant. A gradual increase in the weatherability of the planet’s surface is thought to be the reason for long-term cooling from early Cenozoic ‘greenhouse’ climates to the glacial world of the Pleistocene. Conversely, however, it has also been suggested that temporary weakening of the silicate weathering feedback, through a less weatherable Earth surface, could have also driven transient global warming events in the geological past. The Middle Eocene Climatic Optimum (~40 million years ago), which saw ~4˚C warming over 400,000 years, is the first proposed example of this. If true, this would open the door to an unstable silicate weathering feedback having played a role in other climate events and transitions in the geological past, such as past ocean anoxic events, mass extinctions or glaciations. It would also have implications for predicting the fate of current anthropogenic CO2 emissions, and the trajectory of future climate. Critically, however, the evidence for the silicate weathering feedback being mutable and unstable is still not conclusive. In this project, we will interrogate the geochemical evidence for transient (≤10^5 year) changes in the weatherability of the Earth surface in geological history, using the middle Eocene as a case study. Combining highly precise measurements of stable Li and Si isotopes (established indicators of Earth surface weatherability) over this period, we will quantify how much (if at all) silicate weathering fluxes varied in the middle Eocene. With numerical modelling, we will examine how such variations affected atmospheric pCO2 and, critically, isolate the causal drivers of any changes in land surface weatherability. In doing so, we will determine whether we need to reconsider silicate weathering as not just as a buffer that stabilises global climate, but also potentially a driver of climate perturbations.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigator: Professor Dr. Friedhelm von Blanckenburg
• Cooperation Partner: Professor Dr. Donald E. Penman
• Ehemaliger Antragsteller: Dr. Michael Henehan, until 9/2023