POLYGONAL SURFACE PATTERNS IN THE EAST ANTARCTIC PLATEAU: MORPHOLOGY, GENESIS, STRATIGRAPHIC IMPLICATIONS, AND RELATION TO LARGER-SCALE SURFACE STRUCTURES

The East Antarctic Ice Sheet (EAIS) is the largest reservoir of freshwater on Earth, and past changes in its volume have directly influenced global sea level since the Miocene. Contained within the ice sheet are atmospheric gases from the last million years, which provide an important data record for understanding the link between greenhouse gases and ice sheet evolution. Field excursions to the East Antarctic Plateau are few in count and limited in their spatial extent; therefore the surface of the EAIS remains an understudied locale. Despite this, a remarkable number of traverses observe and comment on surface cracks that are thin (1 cm to 60 cm wide), subvertical, non-planar, and bifurcating at depth. These cracks commonly intersect or connect to form irregular polygons with diameters of 5 m to 10 m in map view. The presence of these cracks is primarily isolated to areas where the surface slope is locally-increased in the prevailing wind direction and depositional rates of blowing snow are low. In these areas, a lack of insolation from snow cover promotes the development of a hard crust of oriented ice crystals by temperature-gradient driven vapor transport and solar-assisted recrystallization. The resemblance of the cracks to polygonally-patterned ground common in tundra and permafrost environments has sustained the long-standing hypothesis that the structures are formed by thermal contraction.

To advance our understanding of the patterned ice, we apply both observational and numerical modeling techniques. Patterned ice is mapped and described using WorldView satellite images covering a few locations on the ice sheet. We present examples of polygon forms and make comparisons to known types of patterned ground. We numerically model thermally-induced stress in ice to test the thermal contraction origin of these cracks. We discuss the geographic proximity of patterned ice and ice sheet crevasses and develop hypotheses on the interrelation between the two. We discuss the form of these cracks in cross-section from published descriptions and reiterate that the structures assist in mixing modern atmosphere into the pores of relatively old ice, thereby blurring the resolution of paleoclimate records from deep Antarctic ice cores.