ALBERT

Description: The ability of models to elucidate climate and ice sheet dynamics at the Eocene-Oligocene climate transition (34 Ma) is limited by a reliance on present-day topography as a boundary condition. We present a reconstruction of the Antarctic palaeotopography at the E-O boundary that restores sediment eroded from the continent. Estimates of sediment volume surrounding Antarctica constrain our restoration. Using data from coring and seismic imaging and allowing for a moderate biogenic fraction, weathering reactions and sediment porosity, a source volume of 5-13 million cubic km is thought to have been removed from an area of ca. 13 million square km. Changes to the East Antarctic landscape by local, regional and continental-scale ice have been estimated using an ice sheet and erosion model. Material is restored in response to basal conditions under a range of modelled ice-sheet configurations. These models can restore 3-4 million cubic km to East Antarctica. In West Antarctica, factors including the variable position of the grounding line make it impractical to use quantitative erosion models. Here we link geological evidence for known or suspected remnants of Eocene topography with our understanding of processes and patterns of erosion and deposition to drive construction of potential surfaces. There are several options for geologically reasonable surfaces that imply 5-10 million cubic km of eroded volume. The uncertainty in eroded volume is muted by the transformation to palaeo-elevation because isostatic compensation generally limits the change in average regional elevation to 15-20% of the thickness eroded.

Description: ANTscape is a project of the Antarctic Climate Evolution (ACE) Research Program to develop a series of maps to show changes in Antarctic paleotopography over the last ~100 million years. The reconstructions will provide a base for summarising a range of paleoenvironmental data, and for use as inputs for the next generation of ice sheet-ice shelf models. The present-day bedrock topography from the SCAR BEDMAP project will be used as a starting point for reconstructing past paleotopography, moving to BEDMAP 2 when it becomes available. Six maps, one for each significant climatic regime or shift, are planned: 4, 14, 34, 50, 70 and 92 Ma. Work is well advanced on the map for 34 Ma (Wilson and Luyendyk, 2009, Geophysical Research Letters). This is a time that is far enough back for there to be a significantly different topography, but not so far back that reconstruction is seriously unconstrained. It is also of great interest to paleoclimatologists as the largely ice-free landscape on which the first continental ice-sheet formed. The maps prepared by ANTscape will depend not only on restoration of Antarctic continental geography by reversing tectonic movements and elevation changes, but also the restoration of sediment eroded from the continent and deposited around and beyond the Antarctic margin. This will require modeling changes to the Antarctic landscape from erosion (Jamieson et al., 2010, Earth & Planetary Science Letters) and estimates of sediment volumes through the Circum-Antarctic Stratigraphy and Paleobathymetry Project (CASP). For further information see www.ANTscape.aq

Description: ANTscape is an ACE project to develop over the next three years a series of maps to show the changes in Antarctic paleotopography over the last ~100 million years. The reconstructions will provide a base for summarising a range of paleoenvironmental data, and be useful both as inputs for the next generation of ice sheet-ice shelf models, and for credible and realistic visualization of past landscapes to promote wider appreciation of past changes in the Antarctic environment. The first meeting of the group in April 2009 in Leeds agreed that for younger periods (Cenozoic) the present-day bedrock topography from the SCAR BEDMAP project would be a useful starting point for reconstructing past paleotopography, moving to BEDMAP 2 when it became available. However for older periods researchers would have to draw more on current knowledge of plate movements, tectonic deformation, thermal evolution and personal geological experience. Because of the scarcity of geological data, it was recognised that the reconstructions would entail considerable geological interpretation. However it was acknowledged that even poorly constrained reconstructions would be a significant improvement on the current practice of using present day topography for models of past ice sheets, when we know past topography was different.The following six time slices, each representing a significant climatic regime or shift, were proposed for a map: 4, 14, 34, 50, 70 and 92 Ma, with work beginning first on a map for 34 Ma. This is a time that is far enough back for there to be a significantly different topography, but not so far back that reconstruction is seriously unconstrained. It is also of great interest to paleoclimatologists as the largely ice-free landscape on which the first continental ice-sheet formed. The group leader for this time slice is Doug Wilson. The group decided the maps could most conveniently be developed by considering the Antarctic as comprising three large regions: 1) West Antarctica: Marie Byrd Land, Antarctic Peninsula, Ellsworth Mountains, West Antarctic rift system, Weddell Sea and Ross Sea, 2) East Antarctica including Transantarctic Mountains, and 3) the Antarctic margin, comprising the continental shelf and slope as far as the continent- ocean transition. A number of procedural issues are under discussion by ANTscape members, and input is sought from ACE 2009 participants in order that the issues be resolved in 2009. These include the primary geospatial tools to be used, spatial resolution of the primary product, the organizational scheme for gridding the data, and data/document storage and access. For the moment a report on the Leeds workshop along with abstracts and many of the presentations given there can be found at http://groups.google.com/group/antscape?hl=en The maps prepared by ANTscape will depend not only restoration of Antarctic continental geography by reversing tectonic movements and elevation changes, but also the restoration of sediment eroded from the continent and deposited around and beyond the Antarctic margin. This will require close collaboration with ROSSmap and the Circum-Antarctic Stratigraphy and Paleobaythmetry Project (CASP).