SEMINAR - Richard Norris

Ice, Alligators, and Hot-tubs in the Cretaceous Super-Greenhouse

Richard Norris

Scripps Institution of Oceanography

University of California San Diego

Wednesday, March 5th

It is generally accepted that there were no large glaciers on the poles prior to the development of the Antarctic ice sheet about 33 million years ago which initiated the “Icehouse world”. Before this, the world was in a “greenhouse” state which reached the warmest temperatures of the past ~300 million years during the “Cretaceous Thermal Maximum” about 91 million yeas ago. I show that despite very warm conditions during the Cretaceous Thermal Maximum, with tropical ocean temperatures of 35-37°C [95-98.6°F], an ice sheet about 50-60% the size of the modern Antarctic ice cap existed for about 200,000 years. The common assumption that substantial ice could not have existed during past super-warm climates is apparently wrong. Certainly, ice sheets were much less common during the Cretaceous Thermal Maximum than they are during more recent “Icehouse” climates, allowing tropical plants and animals like breadfruit trees and alligators to occasionally frequent the high arctic. However, paradoxically past greenhouse climates may actually have aided ice growth by increasing the amount of moisture in the atmosphere and creating more winter snowfall at high elevations and high latitudes.

See also: Bornemann, A., Norris, R.D. et al. 2008, Isotopic evidence for glaciation during the Cretaceous supergreenhouse: Science 319:189, DOI: 10.1126/science.1148777.