Neogene ice sheet cyclicity in the western Amundsen Sea Embayment – evidence from seismic records

Motivation:
The dynamics of ice-sheets in response to climate changes becomes increasingly a focus of research. In this regard the glacial history of the Amundsen Sea sector of the West Antarctic Ice-Sheet (WAIS) is of particular interest. A potential deglaciation and collapse of the Thwaites and Pine Island glacier drainage basins alone would result in a global sea level rise of approximately 1.5 m. In order to predict the future development of the WAIS and its impact to sea level it is important to put the recent changes into context with the dynamics and development of the ice sheet in the geological past.


Figure 1. Bathymetric map of the western Amundsen Sea Embayment with the location of the seismic reflection lines AWI-20060003 to AWI-20060007 focused for this application (red). Yellow lines mark further AWI seismic reflections profiles. Black lines show the available single-channel seismic reflection profiles of the British Antarctic Survey (BAS). Dashed red lines mark proposals for further seismic reflection sections.

Methods and material:
Our project is based on new multichannel seismic reflection data collected in the western Amundsen Sea Embayment as part of the RV Polarstern cruise ANT-XXIII/4 (2006) (Fig. 1). Five seismic profiles of high-resolution offer a record of the glacial development and processes in the western Amundsen Sea Embayment during the Neogene. To supplement details for the uppermost sedimentary layers, Parasound profiles of this cruise were incorporated. Additionally, several single-channel reflections lines of the British Antarctic Survey are at our disposal (Fig. 1). The records offer conclusions to ice-sheet variations which left typical traces such as configuration of layers, structures of mass movements and grounding zone wedges, or hiati. Also changes in the sedimentary properties are reflected in the character of seismic data, and, furthermore, seismic profiles give a spatial picture of the location and shift of depocentres.

Aims and Proceeding:
In order to approach the link between past and future development of the WAIS, the primary objectives and aims of our project consist of the following:
1. Mapping of the acoustic basement of the Amundsen Sea embayment and its structure with seismic methods to obtain the tectonic geometries and boundary conditions constraining the sediment transport and depositional processes.
2. Analyses of the youngest sedimentary sequences since the Oligocene across the shelf, slope and the continental rise of Pine Island Bay, using the high-resolution multi-channel reflection seismic, sub-bottom profiler and swath-bathymetry data in order to derive a depositional model which sheds light on the sediment transport processes.
3. Correlation of sub-bottom profiling data with sediment core analyses to determine physical and stratigraphic parameters of the youngest deposits and to reconstruct depositional and erosional events in space and time.
4. Construction of a model of ice-sheet advances and retreats in Pine Island Bay throughout the Quaternary. Of particular focus will be the retreat history since the last glacial maximum (LGM).

Outlook
The results of the first phase of this project have demonstrated that a first depositional model can be derived for the western Amundsen Sea Embayment from the scarce seismic and Parasound datasets collected in 2006. The first phase also shows that important links to data in the eastern Embayment and to other regions are missing in order to better constrain the sequence and age model. This requires three further main objectives: (1) linking the datasets to those of the eastern embayment and other regions (Fig. 1, yellow, black), (2) densifying the seismic grid on the middle and outer shelf (Fig. 1, dashed red), and (3) identifying potential drill sites for a drill proposal.

Scientists

Estella Weigelt
Section of Geophysics
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven

Karsten Gohl
Section of Geophysics
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven

Gabriele Uenzelmann-Neben
Section of Geophysics
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven

Research areas

Western Amundsen Sea Embayment, West Antarctica

Publications

Weigelt E, Uenzelmann-Neben G, Gohl K, Larter RD (submitted). Reflection-poor columnar structures: Evidence for dewatering veins in the Neogene sedimentary sequences of the Amundsen Sea Embayment, Antarctica.

Weigelt, E., Gohl, K., Uenzelmann-Neben, G. and Larter, R.D. (2009). Late Cenozoic ice sheet cyclicity in the western Amundsen Sea Embayment - Evidence from seismic records; Global and Planetary Change, 69, 162-169, doi:10.1016/j.gloplacha.2009.07.004.

Scheuer C, Gohl K, Eagles, G, 2006. Gridded isopach maps from the South Pacific and their use in interpreting the sedimentation history of the West Antarctic continental margin; Geochemistry, Geophysics, Geosystems (G3), vol. 7, no. 11, doi:10.1029/2006GC001315.

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Research funding organisation

German Research Foundation

Project number: GO 724/9-1 and 9-2
Funding period: July 2007 - July 2010