SEA-LEVEL CHANGES DURING CRETACEOUS TO CENOZOIC HOTHOUSE, COOL GREENHOUSE AND ICEHOUSE WORLDS

Sea-level history reflects the thermal and cryospheric evolution of the Earth, providing a history of ice sheet behavior and operation of the climate systems under ice-free conditions. We evaluate Late Cretaceous to Cenozoic sea-level variations using two methods: 1) backstripping of shallow water section that provide a direct, albeit discontinuous records of regional change; and 2) scaling deep-sea oxygen isotope records using Mg/Ca to remove temperature effects. Peak warmth, sea levels, and ice-free condition occurred in the Hothouse intervals of the Cenomanian-Santonian (ca. 100-80 Ma) and Early Eocene (56-50 Ma). Hothouse global average sea level falls of ~15 m are associated with oxygen isotope increases that reflect primarily high latitude coolings and may reflect the growth of small ice sheets in elevated regions of Antarctica. However, these purported Hothouse ice sheets are at or below the detection level of the oxygen isotope proxy (0.15‰ = 15 m). Cool greenhouse (Campanian to Paleocene, Middle to Late Eocene) sea-level changes of 15-25 m were caused by growth and decay of small (25-35% of modern) ice sheets, reaching ice-free condition during most, but not all, of the Early Eocene and much of the Paleocene and Middle Eocene. For example, the Middle Eocene Climate Optimum (MECO) was bracketed by ~30 m glacioeustatic falls. Warm periods in the Icehouse of the past 34 Myr displayed different sea-level responses. During the largely unipolar Icehouse of the Oligocene to Early Miocene, the East Antarctic Ice Sheet (EAIS) was not permanently developed, with periods of with large-scale (~40-55 m sea level equivalent) growth and collapse. During peak warmth of the Miocene Climate Optimum (MCO; ~17-15 Ma) ice volume changes were small (generally <20 m). A permanent EAIS developed following 3 middle Miocene oxygen isotope increases (14.7, 13.8, and 13.2 Ma) that were largely cooling events associated with <40 m sea-level falls; the subsequent EAIS post 13.8 Ma was stable (~20-30 m sea-level variations on Myr scale). Despite only moderate atmospheric CO₂levels (400±50 ppm), during the peak warmth interval of the Pliocene, sea levels peaked in Chron G17 (ca. 3 Ma) at 22±10 m and 31±10 m during Gi13 (ca. 3.8 Ma) above requiring loss of Greenland, West Antarctica, the Wilkes and Aurora Basins of East Antarctica.