Constraining the amplitude of Late Oligocene bathymetric changes in western Ross Sea during orbitally-induced oscillations in the East Antarctic Ice Sheet: (2) Implications for global sea-level changes

Abstract

Calibrations of deep-sea δ18O ice volume records imply glacial–interglacial (G–I), eustatic sea-level fluctuations of 10–30 m during the Late Oligocene. But it has hitherto not been possible to evaluate these inferred changes from direct evidence for coeval oscillations of sea-level and changes in the volume of the Antarctic ice sheets. Here we utilise a grainsize-derived paleobathymetry curve [Dunbar, G.B., Naish, T.R., Powell, R.P., Barrett, P.J., this volume. Constraining the amplitude of late Oligocene bathymetric changes in western Ross Sea during orbitally-induced oscillations in the East Antarctic Ice Sheet: (1) Implications for cycle stratigraphic models. Palaeogeography, Palaeoclimatology, Palaeoecology], to determine the amplitude of eustatic sea-level fluctuations, from three well-dated, Late Oligocene, shallow glacimarine sedimentary cycles cored by the Cape Roberts project in western Ross Sea. Our approach estimates the eustatic sea-level contribution to the paleobathymetry curve by placing constraints on total subsidence, decompacted sediment accumulation and glacio-isostasy. These sedimentary cycles link the extent of the East Antarctic Ice Sheet, and local paleobathymetry changes directly to orbital cycles, by using a new chronostratigraphy that enables the three sedimentary cycles to be correlated with individual cycles on the new astronomically-tuned δ18O timescale. Our new eustatic estimates are consistent with the Late Oligocene δ18O-to-sea-level calibrations of Pekar et al. [Pekar, S.F., DeConto, R.M., Harwood, D.M., 2006. Resolving a late Oligocene conundrum: Deep-sea warming and Antarctic glaciation. Palaeogeography, Palaeoclimatology and Palaeoecology 231, 29–40], and show that eustatic sea-level fluctuated between 10 m and 40 m, and represented ice volume fluctuations involving 15% to 60% of the present day Antarctic Ice Sheet. Moreover, our eustatic estimates imply a δ18O calibration for the Mi-1 excursion that supports a significant expansion of ice on Antarctica, perhaps equivalent to 120% of the present day EAIS (assuming no northern hemisphere ice), with an attendant fall in global sea-level of ~50 m.