Limited Recharge of a Steady Deep Groundwater Aquifer in the Southern
Highlands of Early Mars
Abstract
To determine plausible groundwater recharge rates on early Mars, we
develop analytic and numerical solutions for an unconfined steady-state
aquifer beneath the southern highlands. We show that the aquifer’s mean
hydraulic conductivity, $K$, is the primary constraint on the
plausible magnitude of mean steady recharge, $r$. By restricting
groundwater upwelling to Arabia Terra, using a mean hydraulic
conductivity of, $K$ ${\sim}10^{-7}$ m/s, and
varying shoreline elevations and recharge distributions, the mean
recharge must be order of $10^{-2}$ mm/yr. Recharge for other
values of $K$ can be estimated as $r$
${\sim}10^{-5}\,K$. Our value is
near the low end of previous recharge estimates and two
orders-of-magnitude below the smallest precipitation estimates. This
suggests that, for a steady hydrologic cycle, most precipitation forms
runoff, not groundwater recharge. It is also plausible the transient
aquifer response to recharge is sufficiently slow that no upwelling
occurs prior to cessation of climatic excursions causing precipitation.