Tectonic Evolution of the Weddell Sea
Geological Influence on the Onset of Fast Moving Ice

by Michael Studinger, Lamont-Doherty Earth Observatory

West Antarctic Ice Sheet Ice Stream Onsets

Figure 1: Geologic features such as sedimentary basins and subglacial volcanoes are believed to exert an influence on the dynamic behavior of the overlying ice sheet. These features can be mapped using aerogeophysical data combined with interpretation techniques. The image (C) shows sedimentary basins beneath fast-moving West Antarctic ice streams as interpreted from subglacial topography, aerogravity, and aeromagnetic data. These ice streams drain the West Antarctic Ice Sheet. It is believed that the sedimentary basins, together with subglacial water, provide the necessary lubricant to enable rapid basal flow within ice streams. a) Moderate Resolution Imaging Spectroradiometer (MODIS) image mosaic of the onset region of West Antarctic ice streams (data source: NSIDC). The image is 330 by 330 km wide. b) Sub-ice topography from ice-penetrating radar data of the same area [Studinger et al., 2001]. c) Free-air gravity map with interpretation of sedimentary basins superimposed [Studinger et al., 2001].

Geological Influence on the Onset of Fast Moving Ice

My work in West Antarctica focuses on the geological control of fast moving ice called ice streams. The West Antarctic Ice Sheet (WAIS) is the only marine ice sheet, which remains from the last glacial maximum (see map). The base of the ice sheet is grounded on bedrock well below sea-level, and much of the perimeter is surrounded by floating ice shelves. A potential rapid disintegration (collapse) of the West Antarctic Ice Sheet, triggered by anthropogenic climate change, was first described by Mercer [1978]. Since then, an ongoing debate focuses on a possible collapse of the grounded interior reservoir, which would result in an eustatic sea-level rise of 5-6 m. Fast moving ice streams drain the interior ice sheet reservoir playing a critical role in a possible instability of the ice sheet. However, the factors controlling the initiation of ice stream onset are a matter of debate. Evidence is emerging that highly erodable soft sedimentary basins formed in an extensional regime may provide a fixed geologic template for ice streaming. Such basins are likely part of the complex geologic structure of the West Antarctic rift system, a region of elevated heat flux and active subglacial volcanism. Geographically fixed ice stream onsets linked to underlying geological structures may modulate the ice sheet’s response to changes in the global climate system.

I am evaluating the influence of the subglacial geology on the initiation of ice streaming using integrated sets of airborne geophysical data, including gravity, magnetics, ice-penetrating radar and laser altimeter measurements linked to the velocity distribution within the ice sheet mapped by synthetic aperture radar interferometry (InSAR) and ground based ice surface velocity measurements. My work shows, that the distribution of subglacial sediments and fault-bounded sedimentary basins appears to pin the locations of ice stream onsets and lateral margins. Significant ice flow occurs exclusively in regions covered by subglacial sediments supporting the concept that subglacial geologic structures play an important role in the dynamic behavior of ice streams and bear the potential to modulate the dynamic response of the ice sheet to global climate change.

Onset of Ice Streams in WAIS

Figure 2: a) Isostatically adjusted subglacial topography map from Studinger et al. [2001]. Grey areas indicate data gaps. b) Free-air gravity anomaly. Contour interval is 10 mGal. Black dashed line outlines sedimentary basin from Bell et al. [1998]. Heavy white lines outline fault-bounded sedimentary basins: NRB, northern rift-shoulder basin; ORB,Onsetset rift basin; SRB, southern rift-shoulder basin. c) Complete Bouguer anomaly map. Contour interval is 10 mGal. The Whitmore Mountains crustal block is the region southwest of the rift shoulder. e) Distribution of marine sediments and fault-boundedsedimentary basins f). Ice flow tributaries are outlined by a smoothed 25 m/year velocity contour from Joughin et al. [1999] with the exception of the small tributary marked by 2 (10m/year). Arrows indicate velocities from Price and Whillans, 1998. Dashed line marks regions were ice flow appears to be controlled by the distribution of sediments. Question marks indicate data gaps in the interferometric velocity grid. See Studinger et al. [2001] for details.

Publications related to Geologic Control on Fast Ice Flow:

Studinger, M., Bell, R.E., Blankenship, D.D., Finn, C.A., Arko, R.A., Morse, D.L., and Joughin, I., Subglacial Sediments: A Regional Geological Template for Ice Flow in West Antarctica, Geophys. Res. Lett., 28(18), 3493-3496, 2001 doi:10.1029/2000GL011788.

Blankenship, D.D., Morse, D.L., Finn, C.A., Bell, R.E., Peters, M.E., Kempf, S.E., Hodge, S.M., Studinger, M., Behrendt, J.C., and Brozena, J.M., Geologic controls on the initiation of rapid basal motion for the West Antarctic ice streams; A geophysical perspective including new airborne radar sounding and laser altimetry results, Ant. Res. Ser., 77, 105-121, 2001.

Publications related to the West Antarctic Rift System:

Studinger, M., Bell, R.E., Finn, C.A., and Blankenship, D.D., Mesozoic and Cenozoic extensional tectonics of the West Antarctic rift system from high-resolution airborne geophysical mapping, In: J.A. Gamble, D.N.B. Skinner, and S. Henrys, Antarctica at the close of a millenium, R. Soc. of NZ Bull., 35, pp 563-569, 2002. Download PDF file (376 Kbyte).

Bell, R.E., Studinger M., Karner, G.D., Finn, C.A., and Blankenship, D.D., Identifying major sedimentary basins beneath the West Antarctic Ice Sheet from aeromagnetic data analysis, in: D.K. Fütterer, D. Damaske, G. Kleinschmidt, H. Miller, F. Tessensohn, (Eds), Antarctica: Contributions to global earth sciences, Springer-Verlag, Berlin Heidelberg New York, pp. 117 - 122, 2006.

Karner, G.D., Studinger, M., Bell, R.E., Gravity anomalies of sedimentary basins and their mechanical implications: Application to the Ross Sea basins, West Antarctica, Earth Planet. Sci. Lett., 235, p 577 - 596, 2005. doi:10.1016/j.epsl.2005.04.016.

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This work was supported by:

The National Science Foundation,

The Lamont-Doherty Earth Observatory.