Eocene Hyperthermals

10/16 Eocene Hyperthermals – or rapid & extreme warming events as documented in Wyoming, Presented by Ellen Currano, University of Wyoming.

Wyoming fossils are world famous, particularly those from the Paleocene and Eocene (66-34 million years ago). Using our trusty picks and shovels, we can travel back in time to a Wyoming covered in palm trees and alligators and resembling modern-day Florida. Climate was not static during this hothouse interval, however. Researchers using a wide variety of paleontological and geological methods have discovered that a series of abrupt global warming events, or hyperthermals, occurred during the early Eocene. These hyperthermals were caused by the release of carbon into the atmosphere, and the combination of increased CO₂and temperature profoundly affected living things. Studying biotic change during hyperthermals provides insight into how present-day ecosystems will respond to anthropogenic CO₂release.

Sediments in the Bighorn Basin, northwest Wyoming, preserve fossil leaves from the first two Eocene hyperthermal events, the Paleocene-Eocene Thermal Maximum (PETM, 56 Ma) and the Eocene Thermal Maximum 2 (ETM2, ~53.7 Ma). During the PETM, carbon dioxide levels at least doubled, and temperature increased by about 8^oF in the Bighorn Basin. There was a nearly complete change in vegetation, an increase in the diversity of insect herbivore damage traces observed on fossil leaves, and an increase in the amount of leaf area consumed by insect herbivores. After the PETM, both floral composition and insect herbivory returned to pre-PETM states. Changes in CO₂and temperature during the ETM2 were about half that of the PETM, and vegetation and insect herbivore damage at the ETM2 site is intermediary between PETM and background Eocene conditions. Our results demonstrate that ecosystem change scales with the magnitude of change to the carbon cycle and temperature. Because anthropogenic CO₂release is 10-100x faster than that during the PETM, ecosystem change is likely to be even more drastic than that observed 56 million years ago.  Video