Mathematics – Logic
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p31a0122h&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P31A-0122
Mathematics
Logic
0454 Isotopic Composition And Chemistry (1041, 4870), 0702 Permafrost (0475), 0738 Ice (1863), 5754 Polar Regions
Scientific paper
Typical of many hyper arid soils of the Dry Valleys of Antarctica, soils in Victoria Valley contain ~10% ice (at 0.3 m depth) and ~0.4% salt, mostly calcium and sodium sulfates and chlorides, making them excellent analogs to Martian soils. Vapor diffusion models designed to investigate ground ice dynamics on Mars are not entirely satisfactory because they lead to the unrealistic expectation that soils in Antarctica should be ice free within a 1000 years of being saturated with ice, and yet even ancient soils characteristically contain abundant ice near the surface. Validation of these diffusion models has been limited because of the paucity of field based climate and soil climate data. Moreover the models ignore the significant effects of snow cover, surface melt water and salts on vapor fluxes. To better understand the presence and stability of the shallow subsurface ice we are exploring the effect of snow cover and salts on vapor fluxes. Ice stability was investigated using high-resolution climate and soil temperature data from 2002 to 2005. According to the vapor diffusion model ice sublimates at an average rate of 0.22 mm a-1, corresponding to an ice recession of ~1.3 mm a-1 for soil with 10% ice content. Some of the water vapor is transported to the atmosphere; however, some water vapor accumulates at depth in the soil. Furthermore, snow cover during the summer may substantially reduce annual ice loss. Stable isotopes (δ18O & δD) in ice along a 1.6m vertical soil profile reveal a deuterium excess (-13 to -77 ‰) with the greatest enrichment of heavy isotopes at the top of the ice cement and decreasing with depth to form a concave-down profile. This isotopic profile was interpreted using a quantitative model of H2O transport in perennially frozen soil, including the advection-dispersion of heavy isotope- enriched surface water into the ice-cement. It suggests an average infiltration rate of 0.7 mm a-1 of brine if 2.5% of the H2O present is unfrozen, a quantity supported by salt concentration and the temperature record. According to the solute content and temperature of these soils and phase equilibria, sulfates mostly gypsum (CaSO4 2H2O), and mirabilite (Na2SO4 10H2O) are present in dry and ice rich soils. Dry soils, due to hydration have the potential to store 7.5 mm of water in the top 0.22 m of dry soil. Both the sublimation and advection-dispersion model suggest that summer snow events significantly affect ice stability. More realistic estimates of the effect of snow on the annual sublimation rates require field data on the timing and duration of snow cover, and the formation of snowmelt water and surface recharge of subsurface ice. The abundance of hydrated salts in dry soils and first measurements of contrasting water contents at different humidities strongly suggests that the role of salts in the storage and transport of H2O in cold, dry soils needs to be evaluated. This seems to be even more important as recent investigation on Mars indicate that the hydrological cycle on Mars may have been strongly influenced by dehydration reactions of sulfate salts.
Hagedorn Benjamin
Hallet Bernard
Sletten Ronald S.
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