West Antarctic Ice Sheet evolution: New insights from a seismic tomographic 3D depth model in the Eastern Ross Sea (Antarctica)

This work presents the results of the research project WISE (West Antarctic Ice Sheet Evolution) the main aim of which is to provide new insights about WAIS (West Antarctic Ice Sheet) evolution in the Eastern Ross Sea (Antarctica) since the late Miocene times, from morphological and geophysical analysis of glacial sediments. A square grid of 1230 km high-resolution multi-channel seismic reflection data, multi-beam bathymetry data and nine Sound Velocity Profiles (SVP) were collected in January 2006 from the northwestern sector of the Glomar Challenger Basin (Eastern Ross Sea), and tied to Deep Sea Drilling Program site 271. This work provides a detailed seismic stratigraphic analysis of the Miocene-Quaternary Ross Sea Sequences (RSS) 5-8, previously mapped using regional lower-resolution seismic profiles. Eight seismic units are identified on WISE high-resolution seismic profiles. These units and their boundaries in most of the cases match with previously published stratigraphy, although three new horizons have been identified as reflecting lateral and time-transgressive facies changes. We applied travel time reflection tomography to obtain a detailed 3D model of the investigated area, defined by a depth-seismic velocity volume and by the geometry of 5 selected surfaces. The resulting model is used to reconstruct the geomorphological and depositional history of this sector of the outer continental shelf and to infer ice sheet dynamics during Miocene to Quaternary times. A high velocity anomaly observed in units below the Ross Sea Unconformity 2 (RSU2) of Pliocene age (3-3.7 Ma) is interpreted as indicative of glacial sediments over-compacted by large scale grounding ice sheet expansion. The low velocity of the unit above RSU1 (ca. 0.7 Ma), is associated with normally compacted sediments. Contour depth and isopach maps show migration of the sediment depocenter from RSS-6 to RSS-8, indicating a change in the direction of grounding ice advance over the continental shelf. Acoustic facies and seismic velocity changes occurred during deposition of RSS-8, possibly reflecting a major change in the WAIS dynamics in late Pliocene-Quaternary times. (C) 2009 Elsevier B.V. All rights reserved.