Ice-sheet variations as depicted in seismic records of the Amundsen Sea Embayment, West Antarctica

Estella.Weigelt [ at ]


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. New multichannel seismic reflection data of high-resolution offer a record of the glacial development and processes in this area. We present a first interpretation of five seismic profiles collected in the western Amundsen Sea Embayment as part of the RV Polarstern cruise ANT-XXIII/4 (2006).The sea-floor morphology of the observed area is highly variable. Close to the present coast, a rough topography includes troughs of several 100 m depth which were probably formed by palaeo-icestreams cut through the shelf. Here, the seismic lines reveal hardly any internal sequences. Only some thin sediment pockets (< 80 ms TWT ~ 60 m) in between these steep and rugged structures can be identified.On the middle shelf and outside the troughs, the topography is generally smooth and only shows small surface undulations suggesting a quieter deposition realm which was not directly affected by ice streams. Hard surface matter as revealed in parasound sections indicates the flush away of soft sediments by melt-water streams. Such streams might have also formed the shallow and about 10 km wide channel-like structures observed at some locations.The most interesting features are pronounced northwest-dipping reflector series of more than 1 s TWT thickness (> 800 m), indicating well layered sedimentary units. The strata reveal a striking alternation of reflection-poor, almost opaque, units and sequences of closely spaced, continuous reflectors. This alternation probably represents changes in depositional conditions due to sea level variations or periods of ice-sheet extension. Reflection-poor units probably consist of a homogeneous sedimentary matrix with uniform physical properties. An extended ice-shelf cover may have led to the deposition of diamictites and till. In contrast, high-amplitude reflectors result from marked changes of sedimentary densities and P-wave velocities which are the parameters controlling the seismic reflectivity. During these times, open water conditions might have prevailed which allowed a stronger diversification of deposits. Unfortunately, no age control by drill sites is available for this region. However, borehole records of the ANDRILL project in the western Ross Sea show a similar sedimentary pattern, thats why we tentatively suggest at least 10 cycles of ice-shelf expansions and retreats since the middle Miocene in the western Amundsen Sea Embayment.

Item Type
Conference (Poster)
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Event Details
Koordinationsworkshop, SPP 1158/7, Antarktisforschung, 10.-11. Okt.2008, Köln.
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Weigelt, E. , Gohl, K. , Uenzelmann-Neben, G. and Larter, R. (2008): Ice-sheet variations as depicted in seismic records of the Amundsen Sea Embayment, West Antarctica , Koordinationsworkshop, SPP 1158/7, Antarktisforschung, 10.-11. Okt.2008, Köln .

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