Climate and energy balance of the ground in University Valley, Antarctica

We report 3 years of data from one meteorological and three smaller stations in University Valley, a high-elevation (1677 m) site in the Dry Valleys of Antarctica with extensive dry permafrost. Mean air temperature was -23.4 degrees C. Summer air temperatures were virtually always < 0 degrees C and were consistent with the altitude lapse rate and empirical relationships between summer temperature, distance from the coast and elevation. The measured frost point (-22.5 degrees C) at the 42 cm deep ice table is equal to the surface frost point and above the atmospheric frost point (-29.6 degrees C), providing direct evidence that surface conditions control ground ice depth. Observed peak surface soil temperatures reach 6 degrees C for ice-cemented ground > 15 cm deep but stay < 0 degrees C when it is shallower. We develop an energy balance model tuned to this rocky and dry environment. We find that differences in peak soil surface temperatures are primarily due to the higher thermal diffusivity of ice-cemented ground compared to dry soil. Sensitivity studies show that expected natural variability is insufficient for melt to form and significant excursions from current conditions are required. The site's ice table meets the criteria for a Special Region on Mars, with 30% of the year > -18 degrees C and water activity > 0.6.