Radar signatures beneath a surface topographic lineation near the outlet of Kamb Ice Stream and Engelhardt Ice Ridge, West Antarctica (original) (raw)

2009, Annals of Glaciology

Visible and infrared satellite images reveal numerous lineations on the Siple Coast region of West Antarctica. We used 5 MHz ice-penetrating radar to probe the interior and the bed of the ice sheet beneath a lineation at the boundary between Engelhardt Ice Ridge and flat-ice terrain to the south of the Kamb Ice Stream (KIS) outlet. Results show curved reflectors that emerge from the bed beneath 600 m thick ice. The tops of the reflectors extend about 100m into the ice above the bed, where they become almost horizontal. Apparent reflectivity of the horizontal section is about 20 dB less than that of the bed. We conclude that the likely cause of such strong reflection is sea water that was accreted into basal crevasses when the flat-ice terrain was floating. Internal layers are warped downward just downslope from the basal reflectors. It is thought that the downwarping was caused by localized basal melting in the past. The spatial pattern of downwarping suggests that localized basal m...

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High-resolution radar mapping of internal layers of a subpolar ice cap, King George Island, Antarctica

2004

A GPR survey was carried out to investigate the structure and hydrology of King George Island subpolar ice cap, Antarctica. This study was part of a larger investigation on the mass balance of Lange Glacier (62 ◦ 07’S, 58 ◦ 36’W), an outlet ice mass that is receding. The strongest signal in all reflection profiles is due to the presence of free water. Sections show strong near-surface reflectors sitting on weaker ones above the water table. Below the water table, reflectors become strong again, displaying many discrete events that reach the end of the sections. Varying antenna configuration causes an important distinction in radar response for the same subsurface. A nearby snow and ice core was used to calibrate the top section of the GPR images.

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Radar characterization of the basal interface across the grounding zone of an ice-rise promontory in East Antarctica

Annals of Glaciology, 2012

Radar power returned from the basal interface along a 42 km long profile over an ice-rise promontory and the adjacent Roi Baudouin ice shelf, Dronning Maud Land, East Antarctica, is analyzed to infer spatial variations in basal reflectivity and hence the basal environment. Extracting basal reflectivity from basal returned power requires an englacial attenuation model. We estimate attenuation in two ways: (1) using a temperature-dependent model with input from thermomechanical ice-flow models; and (2) using a radar method that linearly approximates the geometrically corrected returned power with ice thickness. The two methods give different results. We argue that attenuation calculated using a modeled temperature profile is more robust than the widely used radar method, especially in locations where depth-averaged attenuation varies spatially or where the patterns of basal reflectivity correlate with the patterns of the ice thickness.

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Interpretation of radar-detected internal layer folding in West Antarctic ice streams

Journal of Glaciology, 1993

Low-frequency surface-based radar-profiling experiments on Ice Streams Β and C, West Antarctica, have yielded high-resolution images which depict folding of the internal layers that can aid in the interpretation of ice-stream dynamics. Unlike folding seen in most earlier radar studies of ice sheets, the present structures have no relationship to bedrock topography and show tilting of their axial fold planes in the flow direction. Rather than being standing waves created by topography or local variations in basal shear stress, the data show that these folds originate upstream of the region of streaming flow and are advected into the ice streams. The mechanism for producing folds is hypothesized to be changes in the basal boundary conditions as the ice makes the transition from inland ice to ice-stream flow. Migration of this transition zone headward can then cause folds in the internal layering to be propagated down the ice streams.

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A comparison of basal reflectivity and ice velocity in East Antarctica

The Cryosphere, 2010

Ground-based radio echo sounding data acquired along the 1700 km US-ITASE traverse have been used to determine ice attenuation and relative basal reflectivity across the major catchments funneling ice from East Antarctica to the Ross Ice Shelf. We find that basal reflectivity varies locally by up to 40 dB which we interpret as due to changes in the phase state

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