Figure 6
Numerical model results showing the normalized rate of gas diffusion at different levels and the D to H ratio of the diffusing gas in the sample at the beginning of a run with a surface temperature of 210 K and a thermal gradient of 30 K/cm. Total depth is 5 cm (0.05 m). Below 1 cm from the surface, the fluxes become very low, restricting the flow of material. As such, (1) large amounts of gas will condense out before reaching the highly fractionating bottom layers. Also, (2) since condensation greatly exceeds sublimation at depth, the inward-travelling gas is isotopically light, composed principally of H2O.