Permafrost in the Cretaceous supergreenhouse

Area of Science:

• Paleoclimatology
• Geology
• Microbiology

Background:

• Earth's climate history shows cycles of icehouse and greenhouse conditions.
• Supergreenhouse periods are typically assumed to be entirely ice-free.
• The Cretaceous period represents a significant supergreenhouse interval.

Purpose of the Study:

• To investigate the presence and nature of a cryosphere during the Cretaceous supergreenhouse.
• To identify modern analogues for ancient permafrost systems.
• To assess the implications of Cretaceous permafrost for biogeochemical cycles.

Main Methods:

• Geological analysis of Cretaceous plateau desert deposits in China.
• Identification of aeolian-permafrost systems and their modern analogues.
• Microbiological analysis of ancient permafrost samples.
• Comparison with marine cryospheric indicators from the Arctic and Australia.

Main Results:

• Evidence of active permafrost and an associated cryosphere in Cretaceous Chinese plateau deserts (132.49–132.17 Ma).
• A modern aeolian-permafrost system in Xinjiang, China, serves as an analogue.
• Cretaceous permafrost coexisted with marine cryospheric indicators, suggesting ocean-atmosphere coupling.
• The permafrost harbored a diverse microbiome at subtropical paleolatitudes and high paleoaltitudes.

Conclusions:

• The Cretaceous supergreenhouse was not entirely ice-free, featuring active permafrost.
• Cretaceous permafrost may have contributed carbon and nutrients to the ocean-atmosphere system.
• Rethinking the role of permafrost thaw is crucial for understanding past climate dynamics and biogeochemical cycling.