A climate threshold for ocean deoxygenation during the Early Cretaceous.

Area of Science:

• Paleoclimatology
• Geochemistry
• Oceanography

Background:

• Oceanic anoxic events (OAEs) represent global deoxygenation linked to warming and biological crises.
• Volcanic carbon dioxide (CO2) emissions are a suspected driver of OAEs via climate warming.
• The Early Cretaceous OAE1a is a significant OAE, but its drivers and dynamics remain unclear.

Purpose of the Study:

• To resolve the timing and dynamics of processes driving OAE1a.
• To investigate the cause-and-effect relationship between climate forcing and ocean oxygenation during OAE1a.
• To understand the long-term impact of OAE1a on Earth system dynamics.

Main Methods:

• Analysis of marine chemistry and climate records across OAE1a.
• Modeling the interplay between volcanic CO2 emissions, climate thresholds, and ocean deoxygenation.
• Investigating the role of silicate-weathering feedback and orbital forcing.

Main Results:

• Rapid deoxygenation during OAE1a correlates with volcanic CO2 emissions and crossing a climate threshold.
• The silicate-weathering feedback's slow recovery delayed reoxygenation for over 1 million years.
• Post-OAE1a, residual warmth and orbital forcing induced cyclic deoxygenation for another million years.

Conclusions:

• Ocean deoxygenation during OAE1a was triggered by volcanic CO2 emissions crossing a critical climate threshold.
• The Earth system's recovery from OAE1a was protracted due to slow climate feedbacks.
• A tight coupling exists between volcanism, weathering, and ocean oxygen content, regulated by climate thresholds.