Shining a light on the Deep and Dark: complementary seismic and radar measurements of glacier beds

Abstract:

Processes at the base of glaciers and ice sheets are important for controlling their flow speed and direction, as well as for affecting changes in those properties over time. In addition, measuring englacial and subglacial propserties is critical for oceanographic studies (circulation beneath ice shelvs), paleoclimate studies (mapping internal reflecting horizons; measuring the thickness and properties of subglacial sediments), biological studies (estimating the potential for conditions conducive to harboring lifeforms), and many other applications. Some of these properties are relatively stable over time and space, and some can change rapidly. For example, ice shelf basal melt is on the order of meters per year; sediment erosion and deposition varies from nil to meters per year.

Techniques for measuring these properties are many and varied. Here we focus on radar and seismic methods, with emphasis on high-resolution measurements of the bed. We made radar measurements over multiple sites on Whilllans Ice Stream, Kamb Ice Strea, and the Ross Ice Shelf to compare and contrast bed conditions. These measurements were repeated after a two- and four-week interval to monitor change. The radar system used was a broad band multichannel array system optimized for high spatial resolution. Bed reflection phase is compared to internal-horizon phase to estimate change in bed properties. Work was conducted (and repeated) along long traverse lines allowing for measuring spatial and temporal variations in changes in bed conditions.