Penetration of Antarctic subglacial lakes by VHF electromagnetic pulses: Information on the depth and electrical conductivity of basal water bodies

Owing to the high level of absorption of very high frequency radio waves in water, previous investigators of airborne radio echo sounding (RES) data from Antarctica have assumed that the depth of subglacial lakes cannot be measured directly by this method. However, we have identified a number of RES returns from beneath the ice-water interface at the surface of eight subglacial lakes that we have interpreted as being reflected from the lake floor. The returns allow us to measure the depth of subglacial lakes, since the velocity of radio waves in water (33.4 m mu s(-1)) is relatively unaffected by electrical conductivity. Attenuation of radio waves within water is controlled largely by its electrical conductivity. Consequently, by examining the decay of the radio wave amplitude with depth we can gain information about the conductivity of subglacial water bodies. Our results indicate that the minimum water depths of eight subglacial lakes vary between 8 and 21 m. The lakes from which our depth measurements were taken are distributed widely around the ice sheet. Thus it may be concluded for the first time that Antarctic subglacial water bodies are generally at least several meters in depth. By examining the attenuation of radio waves through subglacial water, the electrical conductivity of the water is estimated to be extremely low (i.e., fresh pure water).