The time-dependent physics of ice sublimation through thin layers of till is considered, to determine whether sublimation could be sufficiently slow to permit the preservation of ice for 8 Ma in the Dry Valleys, Antarctica. This could only happen if the ice had been very thick, but other evidence (crystal size, dating of other ice-cored moraines) is not consistent with this possibility. Steady-state models suggest that sublimation is rate-controlled by vapor transport. A time-dependent model coupling vapor concentration, air pressure, temperature and ice concentration is formulated, and the resulting equations solved non-linearly. No transient coupling between vapor concentration, air temperature and pressure that substantially slows down sublimation was found in the numerical experiments. This means either that vapor transport is being slowed down by some unconsidered physical process or that the ice is much younger than 8 Ma.
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