On the secular evolution of groundwater on Mars

We modeled the subsurface transport of H₂O and CO₂ on Mars in a two-dimensional pole-to-equator cross-section, starting with sudden surface freezing representing ancient climate change. We find that excursions to low obliquity strongly drive ice sublimation and subsequent groundwater evaporation at low latitudes. This creates a hydraulic gradient in the saturated zone that moves water equatorward and even sublimates the base of high-latitude ice. Eventually, all H₂O is lost at latitudes less than ∼30°. A subcryospheric vadose zone may be retained at higher latitudes, but ultimately only a few monolayers of adsorbed water will be held. A subcryospheric phreatic zone is preserved in the same regions only where lateral heterogeneity restricts horizontal fluid flow. The predicted contemporary state of Mars is drier and with groundwater-if present at all-in different locations than previously considered.