Radar Evidence For Past Ice Flow on Gemina Lingula in the North Polar Layered Deposits

Details Radar Evidence For Past Ice Flow on Gemina Lingula in the North Polar Layered Deposits Radar Evidence For Past Ice Flow on Gemina Lingula in the North Polar Layered Deposits

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p11d..05w&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P11D-05

Physics

[0726] Cryosphere / Ice Sheets, [5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Understanding the occurrence and significance of ice flow in the Martian polar layered deposits is fundamental to decoding any records of climate they may contain. The shape of surface topography between troughs on Gemina Lingula (GL) corresponds closely to the generic shape set by ice dynamics when flow equilibrates surface accumulation at higher elevations and ablation at lower elevations. This indicates ice flow in the past, with evidence preserved in 'relict topography' between troughs, which is nearly unaltered since the time of flow (Winebrenner et al., Icarus 195, 90-105, 2008). This scenario predicts two properties of near-surface stratigraphy, when traced along putative paths of past ice flow: (1) layers do not intersect the topographic surface in the past accumulation zone; and (2) layers may intersect relict topographic surfaces in the past ablation zone. The first prediction, in conjunction with the shape of surface topography, is a strong test: observation of layer/surface intersections in the putative past accumulation area disproves the scenario. Here we present observations from the Mars Reconnaissance Orbiter Shallow Radar (SHARAD) that support both predictions. At higher elevations on GL, we trace layers in the upper few hundred meters around closed contours formed by radar ground-tracks, and fit a low-order polynomial to the noisy layer elevations, to estimate layer elevations on putative paths of past ice flow. We find no evidence for layer/surface intersections in the past accumulation zone indicated by our earlier interpretation of surface topography. Fortuitously, ice flow paths and radar-ground tracks at lower elevations on GL are, in several instances, nearly parallel and overlapping. We find several instances of layers intersecting the surface of relict topography (as indicated by our earlier interpretation), in the putative area of past ablation. We interpret these observations as further evidence for past ice flow on Gemina Lingula in near-equilibrium with spatially varying surface mass fluxes.

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