Atmospheric carbon dioxide levels (as with other Earth system carbon reservoirs) are regulated by numerous interlinked biogeochemical processes operating on different time scales, collectively known as the global carbon cycle. Increases in CO₂ outgassing are balanced by the chemical weathering of silicate rocks, which sequesters excess CO₂ on timescales of >10⁴ years. This mechanism – known as the silicate weathering feedback – plays a key role in cooling down the planet after transient climate perturbations. Geochemical (continental weathering and weathering intensity proxies) and sedimentological (increase in carbonate and silica deposits) evidence underscores the significance of this temperature-regulating feedback over Earth history.

In this project, we are focussing on a warming event that occurred 40 Myr ago, the Middle Eocene Climate Optimum (MECO). This event is unlike other classical warming events in Earth’s history as it saw about 400 kyr of gradual warming: timescales on which the silicate weathering feedback should respond to moderate CO₂ levels. Instead, carbonate burial rate –an indicator of enhanced silicate weathering – did not increase, and temperature kept on increasing, until this trend was abruptly ended by rapid cooling. This poses the question, was the feedback ‘faulty’ or weakened during the MECO? To answer this question, we are generating records of Si and Li isotopes – proxies for silicate weathering intensity – from siliceous and calcareous microfossils from the Atlantic and Pacific Oceans. This multi-site study aims to build a global picture of the silicate weathering feedback dynamics, and of continental and oceanic carbon cycling processes during the MECO.

Supervisors

• Dr. Michael J. Henehan, School of Earth Sciences, University of Bristol, Dozent / formerly GFZ Section 3.3 Earth Surface Geochemistry)
• Dr. Patrick Frings, 3.3 Earth Surface Geochemistry
• Prof. Dr. Friedhelm von Blanckenburg, Geochemistry of the Earth Surface,Freie University

Time Frame

• September 2021 - August 2024

Funding

• Deutsche Forschungsgemeinschaft (DFG) - Project number 459347757