Isotopic evidence for dynamic continental ice sheets during the latest Cretaceous

For much of the Meso- and Cenozoic epochs, the high latitudes were significantly warmer than at present and especially the Cretaceous world has been generally considered a time of strong greenhouse climate and therefore presumed to be ice-free. Accordingly, the first large permanent ice sheets of the past 100 m.y. originated in the earliest Oligocene (ca. 33.7 Ma), with small ephemeral ones perhaps present during the late Eocene. This broad view of a warm and stable Cretaceous climate has been challenged in recent decades by the publication of a considerable amount of new data suggesting more variability in climate. In this study, we aim to test for potential glaciation episodes in the latest Cretaceous by generating the first ever high-resolution δ¹⁸O_sw record for the late Maastrichtian from Ocean Drilling Program (ODP) Sites 1209 and 1210 (Leg 198, Shatsky Rise, western Pacific Ocean). Our results reveal evidence for a dynamic late Maastrichtian ice sheet waning and waxing on the Antarctic continent. Interglacial periods suggest ice sheets covering 0–19% of the modern Antarctic volume, whereas glacial ice sheets reached 55–80% of the present-day Antarctic ice volume, causing glacioeustatic relative sea-level falls of up to 50 m. Additionally, an ice-free Antarctic continent is further been inferred for the warm climate of the Mid-Maastrichtian Event. These findings indicate that fairly large ice sheets could grow and decay equally rapidly under the climatic conditions of the latest Cretaceous and that the Cretaceous was far from being ice free.