On the Detection of Subglacial Water in the Gamburtsev Subglacial Mountains, East Antarctica
Abstract
The presence of subglacial water has an enormous impact on the dynamics of ice sheets. In addition to the effect of basal lubrication on ice flow, subglacial water can also affect the thermal and mass budgets of ice sheets through basal melting or freezing. During IPY 2008-2009, the multinational AGAP project collected airborne geophysical data, including ice-penetrating radar data, over the Gamburtsev Subglacial Mountains in Dome A, East Antarctica. An ~250x500 km grid of these radar data were used to identify the locations of basal water, relying on the strong reflection of radio energy from an ice-water interface (~10-20 dB higher than from an interface with rock or sediment). After pulse compression and migration, three different methods were applied to identify basal water. The first was the subjective method, in which a human operator manually examined the radar profiles and noted the locations of flat bright reflectors. While this method lacks quantitative rigor, it has the advantage of considering an additional piece of information (morphology) in addition to reflectivity. The next was to determine relative basal reflectivity by removing an empirically determined dependence of bed-returned power on ice thickness. This empirical method has the disadvantage of lacking a theoretical basis, but the advantage of not being dependent on a priori knowledge of the distribution of ice chemistry and temperature. The third method is to determine absolute basal reflectivity from the radar equation by removing the effects of dielectric attenuation. In contrast to the empirical method, this method has a solid foundation in theory, but depends on external sources for knowledge of ice temperature and chemical composition. Unfortunately, in situ data on these parameters simply do not yet exist for the Dome A region, and- given the spatially limited nature of ice cores- in all likelihood will never exist at the resolution required to fully implement this method. Therefore, although we attempt to implement the theoretical method using highly simplified temperature models and ballpark numbers for the concentrations of important chemical species, our preferred method is the empirical method. These methods show generally good agreement, and indicate that the location of water underneath Dome A is largely controlled by the valley network of the Gamburtsev Mountains. Areas of disagreement between the second and third methods could indicate areas where ice temperature and/or chemistry deviates from the mean profile for Dome A.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.C21B0537W
- Keywords:
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- 0726 CRYOSPHERE / Ice sheets;
- 0768 CRYOSPHERE / Thermal regime;
- 0774 CRYOSPHERE / Dynamics;
- 0794 CRYOSPHERE / Instruments and techniques