Report

Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse

Science  11 Jan 2008:
Vol. 319, Issue 5860, pp. 189-192
DOI: 10.1126/science.1148777

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Abstract

The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35°C. High-amplitude sea-level changes and positive δ18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New δ18O data from the tropical Atlantic show synchronous shifts ∼91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.

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