Donald D. Blankenship

Institute for Geophysics
John A. and Katherine G. Jackson School of Geosciences
The University of Texas at Austin

   The Antarctic ice sheet has long been a primary modulator of global 
sea level. The highlands of the Antarctic Plate have been the nursery 
for Antarctic ice sheets at least since the early Oligocene separation 
of Antarctica and Australia. It has been shown in recent years that 
the bedrock of an ice sheet plays a major role in controlling its 
behavior. Because of this, any understanding of the nucleation (and 
disintegration) of the contemporary East and West Antarctic ice sheets 
(as well as their predecessors) will require a  comprehensive 
understanding of the crustal elements of the Antarctic Plate. This 
knowledge must include the boundaries, elevation and paleolatitude of 
these crustal elements through time as well as evidence of their 
morphological, sedimentological and tectono-thermal history.  

   Integrated geophysical measurements required to characterize the 
crustal elements of the Antarctic Plate in preparation for modeling 
ice-sheet evolution include:

1.) Distribution of gravity and magnetic anomalies to characterize 
    subglacial lithology (e.g., sediments, crystalline basement and 
    volcanics), identify crustal boundaries and estimate lithospheric 
    flexure through potential field modeling.

2.) Absolute bedrock elevation (from ice sheet surface elevation and 
    thickness) at a scale suitable for models of both contemporary and 
    paleo-ice-sheet evolution as well as for potential fields 
    modeling.

3.) Detailed subglacial morphology and physical character of the 
    ice-rock interface to identify any "preserved" glacial 
    geomorphology and map fault scarps indicative of Cenozoic (or 
    older) tectonic processes as well as to determine the location, 
    properties and connectivity of subglacial sedimentary units. 

4.) Contemporary basal melt distribution (from ice sheet layering) to 
    estimate the current distribution of geothermal flux for 
    indications of tectono-thermal history and as a necessary boundary 
    condition for models of ice sheet evolution.

   The basic impediment to making these geophysical measurements is 
the subcontinental scale and multi-kilometer-thick ice cover of the
crustal elements of the Antarctic Plate. Because of this, airborne 
ice-penetrating radar has been the primary tool for studying the 
subglacial geology of Antarctica. Much of this geology has been 
inferred from the crude physiography compiled from interpretations of 
widely spaced analog radar profiles collected in the absence of 
complementary geophysical observations. In the last ten years, great 
strides have been made in the technology of airborne radar sounding 
and its integration with airborne gravity, magnetics and laser 
altimetry. I will review the advances in airborne ice-penetrating 
radar from the perspective of the integrated aerogeophysical 
measurements required to understand the role of these crustal elements 
in studies of ice sheet evolution.