| Summary: | Thesis (Ph.D.)--University of Washington, 2015 Subsurface ice is common in regions where mean annual temperatures are below the freezing point of water. Once present, this ice may persist for long periods of time even under unfavorable environmental conditions. Subsurface ice is fundamentally important as a source of water for plants and microbes, a proxy for paleoclimatic information, and a major component controlling the periglacial landscape. This dissertation examines the stability and persistence of ground ice both in the Dry Valleys of Antarctica, a small part of the continent that is not covered in ice, and at the equatorial region on Mars. This research was initially motivated by claims that the ice buried under several decimeters of dry regolith in Beacon Valley is more than 1 Ma old and perhaps over 8.1 Ma, thereby making it the oldest known ice on Earth. My study uses numerical modeling to determine the short-term and long-term rates of sublimation of ground ice; the latter bears directly on the longevity of subsurface ice. The modeling utilizes extensive soil and environmental data from a well characterized site in Beacon Valley. One component of the model is to reconstruct subsurface temperatures based on measured surface temperatures. It is validated using ground temperature measurements. Both thermal and sublimation components of the model are then coupled, along with environmental data from the Curiosity Rover, to numerically simulate the sublimation of ground ice in Gale Crater, and to consider the potential for ground ice to have persisted there for long periods of time. The contemporary sublimation rate of ground ice in Beacon Valley, Antarctica is modeled using a vapor diffusion model constrained by 12 years of climate and soil temperature data, and field data of episodic snow cover and snowmelt events that have not been represented in previous models of the ground ice sublimation. The model is extended to reconstruct the sublimation history over the last 200 ka using paleotemperatures ...
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