The Eastern Ross Sea continental shelf during the Cenozoic: implications for the West Antarctic ice sheet development

Abstract

The present-day bathymetric profile in the Ross Sea, as in other regions around the Antarctic margin, is deepening landward and shows unusually high water-depths: up to 1000 m in the inner shelf. These two features are the product of multiple ice sheet advances and retreats on the continental shelf. In this paper, we present a reconstruction of paleo-bathymetric profiles of the Eastern Ross Sea throughout the Cenozoic. The evolution of the sea-floor morphology from shallow and seaward dipping to the present-day configuration gives new insights into the understanding of the West Antarctic Ice Sheet (WAIS) history in this sector. Paleo-bathymetric profiles have been calculated by applying a reverse post-rift modelling, starting from a cross-section derived from multichannel seismic data. The post-rift reverse modelling includes: sediment decompaction, isostatic compensation after removing and recovering sediments of the post-rift thermal subsidence. The major uncertainty in our model is due to the paucity of stratigraphic constraints for the late Miocene and Pliocene sequences that prevents precise values of paleowater-depth being estimated. Nevertheless, major changes in the shape of the continental shelf and slope throughout the Cenozoic can be recognised, and mark some critical steps in the Ross Sea evolution. (1) Pre-Miocene: the Eastern Ross Sea was a deep structural basin bordered to the west by areas (e.g., the Central High) outcropping the sea level and hosting valley glaciers or small ice caps. A continental shelf edge was not clearly developed yet, the eastern flank of the Central High appeared as an inclined ramp, dipping towards the ocean. (2) Early to middle Miocene: tectonic subsidence gradually produced a marine flooding over most of the pre-Miocene sub-aerial areas. A continental shelf, slope and rise are gradually delineated. The shelf profile was seaward dipping and not yet overdeepened. The geometry of the depositional sequences is mainly determined by eustacy, tectonic and sediment supply. (3) Starting from Late Miocene (likely from 10 Ma to at least 4 Ma) the bathymetric profile evolved progressively from seaward to landward dipping and reached an overdeepened configuration, very similar to the present-day profile. Depositional and erosional processes over the continental shelf were largely controlled by ice streams. Outcropping of large parts of the continental shelf during the early Cenozoic has important implications on the volume of the West Antarctic Ice Sheet. At that time, the WAIS contribution to the eustatic fluctuations was most likely much larger than today.