Middle Eocene greenhouse warming facilitated by diminished weathering feedback

Area of Science:

• Paleoclimatology
• Geochemistry
• Carbon Cycle Science

Background:

• The Middle Eocene Climatic Optimum (MECO), a ~500-kyr global warming event ~40 million years ago, is linked to increased atmospheric CO2.
• The drivers of this CO2 rise and the Earth system's response remain poorly understood.

Purpose of the Study:

• Investigate the cause of elevated CO2 during the MECO.
• Evaluate the role of continental silicate weathering in regulating climate during this period.

Main Methods:

• Analysis of osmium isotope ratios (187Os/188Os) in marine sediments.
• Examination of published carbonate compensation depth (CCD) records.
• Carbon cycle modeling simulations.

Main Results:

• Continental silicate weathering response was diminished during the MECO, contradicting the silicate weathering thermostat hypothesis.
• Early to middle Eocene warmth likely reduced rock weatherability, weakening the silicate weathering feedback.
• This weakened feedback permitted prolonged accumulation of volcanic CO2 in the ocean-atmosphere system.

Conclusions:

• The silicate weathering feedback strength is variable and crucial for understanding long-term climate and carbon cycle dynamics.
• Diminished weathering efficiency during warm periods can lead to significant CO2 buildup, impacting global climate.