Accumulation Patterns and Basal Conditions from Radar Observations Along the US- ITASE Traverse in East Antarctica

Details Accumulation Patterns and Basal Conditions from Radar Observations Along the US- ITASE Traverse in East Antarctica Accumulation Patterns and Basal Conditions from Radar Observations Along the US- ITASE Traverse in East Antarctica

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.c31b0486j&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #C31B-0486

Physics

0726 Ice Sheets, 0762 Mass Balance (1218, 1223), 0776 Glaciology (1621, 1827, 1863), 0794 Instruments And Techniques

Scientific paper

We present short-pulse radio echo reflection profiles recorded along a largely cross-flow transect during the 2006-08 US-ITASE traverse from Taylor Dome to South Pole. We used a 200-MHz system to focus on firn strata within the upper 100 meters and a 4-MHz system to focus on englacial strata, as well as the bed. Within the catchment area of Byrd Glacier unusual cross-cutting englacial horizons, alternating with metamorphic layers representing hiatuses in accumulation, suggest changing patterns of accumulation, possibly caused by long term wind shifts. Profiles recorded by both systems from south of the Byrd catchment area to Titan Dome are conspicuously characterized by buried megadunal type stratigraphy, consistent with the traverse being downflow from the apparent eastern edge of the modern megadunes region. The 200-MHz profiles reveal buried and partially buried foreset beds extending over 25 km in length, up to 50 m thick and sandwiched between 4 to 15 m thick unstratified layers up to 60 km long. These beds are antidunal deposits, and the unstratified layers are glazed, zero accumulation zones of extreme, long term metamorphism. The deeper, 4-MHz profiles show prograding beds occur to 1700 m depth, up to 250 m thick along a segment on the northeast fringe of the megadunes. These impressive features, both near the surface and at depth, show the concentrated way snow has been, and now accumulates, in the megadunes area and well east of it. If these beds formed during high accumulation Holocene warming periods, then we need to understand how they could be interleaved with features characteristic of zero accumulation. The 4- MHz detection of prograded beds must be made possible by embedded, volcanic high conductivity layers, which reveals that these beds contain datable layers. We have also plotted the power received from some 300,000 bed echoes versus ice thickness along the traverse. We use these data to estimate the average 4-MHz signal absorption rate within the ice, which allows us to calculate bed reflectivity and interpret basal properties. The results suggest many areas of thawed basal conditions, generally thought to be rare in East Antarctica. They also depict bed reflectivity at several candidate subglacial lake sites based on satellite imagery and reveal at least one possibly new subglacial lake.

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