![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7dFx_H3NvFd0aAwuR17LnLjiBq50cID-jgIAGKoVBfJPIDVR96DipbVaxrCGQj3hNtDogyp9qi5wiihDWUrtB6eDkNL1ZEAWzJy3GcmxOlIRhWL3EwsS_7DhjRYgRTHLcn5QY/s400/ss3.jpg)
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.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzq_kwZFgYPXMk_XnCHzi1rysdxUp4ubEkSXMdOuO0zXjtJ7EeVbxbLdRyJ4-dN6zLAOIVIokhCZ5GE07aMhw06Q-WuOgpAh4J3RNFeYULwp2Zp0VigltTNoZuOCaTdqRjnEX7/s400/graspg.jpg)
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.