ALBERT

Description: The threat, in terms of sea level rise, posed by the potential rapid deglaciation of West Antarctica means there is an urgent need to know more about the speed and style of marine ice sheet retreat. Quaternary deglacial events recorded in marine sediments provide an opportunity to understand the future of the modern day ice sheet. In this context, we examine the glacial history of a particularly poorly understood sector of the West Antarctic continental shelf the Amundsen Sea Embayment using new data from two recent research cruises. This extended abstract describes how marine geological and geophysical data are being used alongside terrestrial dating methods to understand the full extents, dynamics and retreat pattern of the West Antarctic Ice Sheet in the Amundsen Sea region during the last glacial cycle. These data hold significance for understanding and accurately modelling the stability and climate sensitivity of the West Antarctic Ice Sheet.

Description: The Amundsen Sea continental shelf is one of the remotest areas of coastal Antarctica, and was relatively unexplored until the late 1980s. Over the last two decades, however, oceanographic and geological interest has led to several cruises, one result of which is that there is now sufficient bathymetric data to compile a fairly detailed regional map of the Amundsen continental shelf. We have combined the available multibeam and single beam bathymetry data from this region and created a new regional bathymetric map of the Amundsen Sea continental shelf and slope. After cleaning the individual data sets we used a natural neighbor algorithm to interpolate between the existing data and create a grid at 5 km raster resolution. The most prominent regional feature is a series of separate trough systems along the inner shelf, which are aligned with present glaciers, separated by shallower ridges, and shoaling seaward.

Description: West Antarctica is generally thought to have behaved as a single terranesince mid-Cretaceous time. Subsequently some limited internal deformation,below the resolution of paleomagnetic methods, may have taken place, andthere has been some extension between East and West Antarctica. However,the most dynamic part of the Antarctic plate during Late Cretaceous andTertiary times was the Pacific margin of West Antarctica and adjacentoceanic areas. Unfortunately this is one of the least studied sectors ofthe Antarctic margin, due to its remoteness and inaccessibility.We present new reconstructions of the Pacific margin of Antarctica based onconstraints from marine magnetic data and regional free-air gravity fields.Recent results from interpretation of seismic reflection and gravityprofiles collected in the Bellingshausen Sea are also incorporated. Thereconstructions show regional constraints on the complex tectonic evolutionof the Amundsen and Bellingshausen Seas during and after the breakupbetween New Zealand and West Antarctica. The Late Cretaceous to earlyTertiary development of the region involved interactions between thePacific, West Antarctic, Phoenix (Aluk), Charcot and Bellingshausen plates.The West Antarctic margin consists of two main sectors. The western sectorcomprises the parts of the margin that Chatham Rise and Campbell Plateauseparated from at about 90 Ma and 80 Ma, respectively. Part of this sector,probably including much of the Amundsen Sea continental shelf, wassubsequently affected by independent motion of the Bellingshausen plate. Inthe eastern sector, Phoenix plate subduction continued through the LateCretaceous and early Tertiary, then terminated progressively from southwestto northeast as segments of the Antarctic-Phoenix ridge migrated to theAntarctic Peninsula margin. Between these two sectors is an area withcomplex gravity anomalies near Peter I Island. We suggest that a fragmentof the former Charcot plate, containing the oldest ocean floor adjacent toWest Antarctica, is preserved in this area. Some implications of our newreconstructions can be tested by onshore and offshore deployments ofseismometers along the Pacific margin. Ideally such deployments should beco-ordinated with controlled-source seismic investigations.