Berichtsheft - Deutsche Gesellschaft für Polarforschung eV

Basement and sedimentary architecture of the Amundsen Sea Embayment:
How close do we come to reconstructing West Antarctica’s glacial history?
Karsten Gohl, Gabriele Uenzelmann-Neben, Gerhard Kuhn, Ansa Lindeque, Thomas
Kalberg, Estella Weigelt & Astrid Denk
Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven; karsten.gohl@awi.de
Recent melt and retreat rates of glacier systems in the Amundsen Sea Embayment and, in
particular, Pine Island Bay have placed this region into focus for predicting the dynamics of
the West Antarctic Ice Sheet and sea-level rise (e.g. Pritchard et al., 2009). Observations of
bathymetric features of the continental shelf of the Amundsen Sea Embayment and
identification of tectonic lineaments from geophysical mapping indicate that erosional
processes of paleo-ice stream flows across the continental shelf followed basement
lineaments inherited from the tectonic history since the Cretaceous breakup between New
Zealand and West Antarctica (Gohl, 2011). For instance, east-west oriented basement trends
correlate with coastline trends and overlay tectonic lineaments caused by former rift
activities. Directional trends in northwest-southeast orientation are observed for the glacial
troughs of the western embayment outer shelf, the western Pine Island Bay coastal zones,
and the inner Pine Island glacial trough and are superposed on a distributed southern plate
boundary zone of the former Bellingshausen Plate. The north-south trend of the main Pine
Island glacial trough and the NNE-trend of the Abbot Ice Shelf trough follow the predicted
lineation trend of an eastern branch of the West Antarctic Rift System extending from the
Thwaites drainage basin northward into Pine Island Bay. An understanding of this context
helps constrain the geometries and sea-bed substrate conditions for regional paleo-ice sheet
models (Graham et al., 2009).
The sedimentary architecture of continental shelf and slope represents stages of the glacial
history from early glaciation to the last glacial period (e.g. Lowe & Anderson, 2002; Weigelt et
al., 2009). A new large dataset of seismic profiles collected on the shelf, slope and rise
provides new insight into the glacio-marine processes. The data reveal an heterogeneous
outer shelf with areas of pronounced progradation while other areas lack this deposition type
almost entirely. In some parts, sediments deposited across the shelf break enlarged the
outer shelf by up to 60 km oceanward. Major glacial troughs – systems of ice streams flow –
have repeatedly shifted position, width and direction since early glaciation. These deep
troughs are significant for incursions of Circum-Polar Deep Water onto the shelf. Observed
grounding zone wedges indicate stages when grounding zones where stationary for some
time. These observations show that ice sheet advances on the shelf have constantly altered
throughout glacial cycles. Although chronological control of the strata is still missing, we will
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