GROUND PENETRATING RADAR USE ON THE OLDEST REPORTED GLACIER ICE IN THE WORLD: UNCOVERING MANIFESTATIONS OF ORBITAL VARIATIONS DURING THE LAST 400,000 YRS PRESERVED WITHIN DEBRIS-COVERED GLACIERS OF THE QUATERMAIN MOUNTAINS, ANTARCTICA

Antarctic debris-covered glaciers represent long-term archives of climate change. In addition to preserving ancient atmosphere, the surface topography and distribution of internal debris point to temporal and spatial changes in ice accumulation, ablation, and rock-fall processes at valley headwalls. We show that the spacing and geometry of englacial debris bands and surface ridges on two ancient alpine glaciers are related to cyclical variations in ice accumulation and ablation. Chronological control suggests that these changes are likely related to 100-ky eccentricity cycles, documenting changes in sub-freezing conditions in the Antarctic Dry Valleys that extend back at least 400 ky.

Ground penetrating radar at multiple frequencies is used in conjuction with ice cores, soil excavations, and high-resolution topographic imagery to assess the distribution of englacial and supraglacial debris in the Mullins and Friedman debris-covered glaciers. The first 3.5-km of Mullins Glacier and 2-km of Friedman Glacier displays a series of well-defined, englacial reflectors that originate ~5-20 m above the valley bottom. These reflectors exhibit non-linear dipping angles, and intersect the ground surface near the location of arcuate surface ridges. Examination of shallow ice cores, GPR wave-forms, and the visual inspection of reflector-surface intersections, show that the reflectors are comprised of aligned layers of clasts separated by clean glacier ice. The pattern and distribution of arcuate surface ridges and internal debris bands are nearly identical between Mullins Glacier and adjacent Friedman Glacier, suggesting an origin related to regional factors, rather than to local variability within each glacier. We describe a geomorphic model that links observed surface and subsurface structures to long-term climate change. In this model, the internal debris bands represent (1) the accumulation of rockfall at the glacier head during times of reduced ice accumulation and (2) subsequent burial and englacial transport during rapid periods of renewed ice accumulation. The data suggest that climate records may be gleaned from the surface morphology of debris-covered glaciers, and advocates the possibility of deducing long-term climate change on Mars through analyses of analogous features.