Enhanced clay formation key in sustaining the Middle Eocene Climatic Optimum

Area of Science:

• Paleoclimatology
• Geochemistry
• Carbon Cycle Research

Background:

• The Middle Eocene Climatic Optimum (MECO) was a prolonged global warming event (~40 million years ago) characterized by increased CO2 and ocean acidification.
• The MECO's extended duration is puzzling because silicate weathering should have acted as a negative feedback to reduce CO2.
• Understanding silicate weathering dynamics is crucial for explaining long-term climate events.

Purpose of the Study:

• To investigate silicate weathering processes during the Middle Eocene Climatic Optimum.
• To understand the mechanisms sustaining this long-duration warming event.
• To explore the role of clay mineral formation in the Cenozoic carbon cycle.

Main Methods:

• Analysis of lithium isotope ratios (δ7Li) in carbonate-rich deep-sea sediments as a tracer for silicate weathering.
• Utilizing a box model to simulate weathering processes and carbon cycle feedbacks.
• Comparing lithium isotope data with known climate and geological events.

Main Results:

• A significant positive δ7Li excursion (~3‰) was detected, unique among identified warming events.
• Box model simulations indicate a shift from congruent to incongruent silicate weathering.
• Evidence suggests increased clay mineral formation sequestered cations, disrupting the carbonate-silicate cycle.

Conclusions:

• The MECO's sustained warming was driven by a shift in weathering processes, favoring clay formation over cation release.
• Increased continental volcanism initiated the warming, but clay mineral dynamics prolonged it.
• Clay mineral formation is a key factor in intermediate-timescale (100,000-year) climate events and the carbon cycle.