A COMPARISON OF TERRESTRIAL COLD-DESERT ANALOGS: ANTARCTIC AND ARCTIC LANDFORMS AND IMPLICATIONS FOR REGIONAL GLACIATION ON MARS

The Antarctic Dry Valleys (ADV) are classified as a hyperarid, polar desert. The region has long been considered an important analog for Mars because of its generally cold and dry climate and because it contains a suite of landforms at macro-, meso-, and microscales that closely resemble those observed at the martian surface. The extreme hyperaridity of both Mars and the ADV has focused attention on the importance of salts and brines on soil development, phase transitions from liquid water to water ice, and ultimately, on process geomorphology at a range of scales on both planets. The ADV can be subdivided into three microclimate zones: a coastal thaw zone, an inland mixed zone, and a stable upland zone; zones are defined on the basis of summertime atmospheric temperature, soil moisture, and relative humidity. Subtle variations in these parameters result in considerable differences in the distribution and morphology of: (1) macroscale features (slopes and gullies); (2) mesoscale features (polygons, including ice-wedge, sand-wedge, and sublimation polygons, as well as viscous-flow features, including solifluction and gelifluction lobes, and debris-covered glaciers); and (3) microscale features (rock-weathering processes/features, including salt weathering, wind erosion, and surface pitting). Equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones. Some equilibrium landforms, such as sublimation polygons, indicate the presence of extensive near-surface ice; identification of similar landforms on Mars may also provide a basis for detecting the location of shallow ice. The relative geomorphic and climate stability of the ADV is in stark contrast with measured, large-scale changes in climate and landscapes that have occurred in Arctic regions throughout the Pliocene and Quaternary Periods. Consequently most macroscale (and perhaps mesoscale) landforms in the Arctic reflect the culmination of alternating geomorphic processes operating under a variety of climates. This last point emphasizes the unique aspect of the ADV, its long-term climate stability, and makes it an ideal analog for Mars. Moreover, equilibrium landforms identified in the ADV formed under climate conditions comparable to those described for Mars over geologic time.