Visions of Ice Sheets in a Greenhouse World

The warmest global climates of the last 200 m.y. occurred in late Cenomanian-early Turonian (ca. 95-93 Ma) and latest Paleocene-early Eocene (ca. 55-50 Ma), with bottom-water and high-latitude temperature exceeding 15° C. These intervals of peak warmth were punctuated by cool snaps associated with sea-level drops. The late Cenomanian-early Turonian δ ¹⁸O minimum was bracketed by two large (>0.75%) deep-sea δ ¹⁸O increases (92-93 Ma, mid-Turonian and 96 Ma, mid-Cenomanian recorded at Site 1050). New surface dwelling planktonic δ ¹⁸O data from equatorial Site 1259 also record a similar the mid-Turonian increase, suggesting a global compositional change in seawater. Backstripped eustatic estimates from New Jersey and the Russian platform show large (>25 m) and rapid (<1 m.y.) sea-level changes in the Late Cretaceous to early Eocene (99-49 Ma) that must be attributed to glacioeustasy. The mid-Cenomanian and mid-Turonian δ ¹⁸O increases are associated with major eustatic lowerings, implicating ice growth despite the warm interval bracketing these events. We reconcile records of warm high latitudes with glacioeustasy by proposing that Late Cretaceous-early Eocene ice sheets generally reached maximum volumes of 8-12 x 10⁶ km³ (20-30 m glacioeustatic equivalent), but did not reach the Antarctic coast; hence, coastal Antarctica (hence deep water) remained warm even though there were significant changes in sea level as the result of glaciation. Unlike the Oligocene and younger icehouse world, these ice sheets only existed during short intervals (<100 k.y.) of peak Milankovitch forcing, leaving Antarctica ice-free during much of the greenhouse Late Cretaceous to middle Eocene. These results highlight the need to re-evaluate the paradigm that continental ice sheets did not exist during times of warm high-latitude climates.