Lies Beneath an Ocean of Ice? - How Lithospheric and Crustal Structure of Antarctica Influence 
Ice-Sheet Behavior

Slawek Tulaczyk
Department of Earth Sciences
UCSC
Santa Cruz, CA 95064

One of the most surprising and important recent developments in ice-sheet glaciology was the 
realization that crustal and lithospheric structure may play a profound role in controlling spatial 
and temporal patterns of ice flow. Glaciologists just started to describe and comprehend the 
nature and the strength of this dependence of ice-sheet behavior on subglacial geologic structure. 
This area of inquiry will provide a key frontier in glaciology in the coming decades. From this 
standpoint, the proposed Antarctic Array initiative will provide a timely stream of data and 
concepts, which will feed back into quantitative models of ice-sheet evolution. In Antarctica, the 
continental- and regional-scale structural fabric is clearly 'bleeding through' the relatively thin 
sheet of ice. The most fundamental division of Antarctic ice masses differentiates the large East 
Antarctic Ice Sheet (EAIS) resting mostly above sea level from the smaller, marine-based West 
Antarctic Ice Sheet (WAIS). WAIS appears to be much more susceptible to unsteady behavior 
driven by internal dynamics and/or climate changes. The distinct dynamics of WAIS is 
ultimately related to its tectonic setting within a large continental rift zone. There, the top of the 
crust lies mostly below sea level, geothermal heat flux appears to be elevated, and Tertiary 
sedimentary basins are abundant. All these factors help control the location of fast-flowing ice 
streams, which discharge ~90% of ice from WAIS. The horizontal spacing and width of the ice 
streams (and their tributaries) is quite clearly controlled by basin-and-range-like crustal fabric.
          The 'Holy Grail' of Antarctic glaciology is construction of a quantitative model of the ice 
sheet that would be reliable enough to: (1) reproduce the present-day ice-sheet behavior and (2) 
yield trustworthy predictions of near-future Antarctic contribution to sea level changes. These 
goals can only be achieved if there will be sufficient constraints on spatial distribution of key 
characteristics of subglacial geology (e.g., rock erodibility and geothermal flux). At present this 
spatial distribution is known much less than adequately. The AntarcticArray initiative can 
contribute significantly to the effort of providing proper basal boundary conditions for ice-sheet 
models, particularly in conjunction with the proposed fast-access ice-sheet drilling program 
(FASTDRILL) aimed at subglacial sampling and measurements. In addition to the concern about 
near-future evolution of the Antarctic ice sheet, glaciological community has considerable 
interest in understanding the processes that led to establishment, growth, and stabilization of this 
ice sheet in Cenozoic. On these long time scales one cannot any longer assumed that the tectonic 
template for ice sheet evolution was unchanging. The timing and magnitude of rifting and 
mountain building events may have been key factors in providing 'seeding areas' for ice-sheet 
development and in modulating subsequent ice-sheet development. In this context, it is crucial 
for glaciological models to incorporate a realistic representation of Cenozoic changes in 
lithospheric and crustal structure of the Antarctic continent.