Antarctic Ice Evolution Viewed from NJ and the Deep sea

Backstripping of mid-Cretaceous to Miocene sections from the New Jersey Coastal Plain (ODP Legs 150X and 174AX) provides a eustatic estimate for 100-8 Ma. Backstripping extracts amplitudes of global sea level from passive margin records by accounting for paleo-water depth variations and progressively removing the effects of sediment loading (including the effects of compaction) and tectonic subsidence. Rapid (less than 1 m.y.) sea-level lowerings of 20-35 m are associated with Cretaceous-lower Eocene sequences; eustatic rises approach 50 m in some instances. Middle Eocene lowerings were approx. 45 m. Glacioeustasy is the only known mechanism that can account for these large, rapid changes. 2-D backstripping of Oligocene sequences yields estimates of ~20-60 m for eustatic lowerings. 1-D backstripping yields early Miocene amplitudes of up to 40 m, whereas estimates of middle-late Miocene eustatic change are generally lower (20-40 m). We interpret the sea-level estimates in terms of glacioeustasy and reconcile the sea-level and deep-sea oxygen isotopic records. Because large N. hemisphere ice sheets developed during the late Pliocene, we ascribe these eustatic changes to Antarctic ice-volume variations, and thus, provide a prediction for Antarctic cryospheric evolution. Ephemeral small (20 m sea-level equivalent; ~30% of the modern East Antarctic Ice Sheet [EAIS]) to medium-sized (35 m equivalent; ~50% EAIS) ice sheets existed in Antarctica even during the peak warmth of the Late Cretaceous-early Eocene, although most of the time Antarctica was ice-free. Larger ice sheets (approx. 45 m equivalent, ~70% EAIS) developed in the late middle Eocene (46 and 42 Ma). A large (~54∓ 15 mm) earliest Oligocene drop in sea level was associated with development of a large ice sheet (87% EAIS), though sea level again rose by nearly 46∓ 15 m about 1 m.y. later, suggesting near collapse of the ice sheet. The ice sheet subsequently grew and decayed numerous times in the Oligocene-middle Miocene, testifying to a very dynamic ice sheet between ca. 33 and 14 Ma. By the middle Miocene, the East Antarctic ice sheet had become a permanent feature and sea level changes were primarily controlled by small ice-volume changes in Antarctica and the nascent growth of Northern Hemisphere ice sheets.