Groundwater Flow to Gale Crater in an Episodically Warm Climate.

Orbiter and rover data have revealed a complex and intermittent hydrological history in Gale Crater on Mars, where habitable environments appear to have endured for at least thousands of years. The intermittency may be the result of a dominantly cold climate punctuated by geologically brief periods of warmth and active hydrology. However, the time required to establish an integrated hydrological cycle in a warming climate is difficult to ascertain and has not been thoroughly investigated. Here we model the transient evolution of groundwater flow and subsurface temperature, the slowest evolving components of the hydrological cycle, during a warm departure from cold conditions. We find that tens of thousands of years are likely required before groundwater could be a meaningful source for large lakes in Gale. With highly favorable conditions, primarily high permeability, significant flow might develop in thousands of years. This implies that surface water dominates during the beginning of a warm phase. Annual mean surface temperatures in Gale below 290 K would likely leave the nearby highlands frozen at the surface. In that case, deep aquifers beneath a highlands permafrost layer could deliver water to Gale, where low temperatures would have reduced evaporation. Plain Language Summary: Satellite imagery and data from the National Aeronautics and Space Administration (NASA)'s Curiosity rover indicate that Gale Crater, on Mars, hosted large lakes more than 3 billion yr ago. The climate during this period is not well understood but may have been mostly frozen, only occasionally warming up to the point where lakes could form. If so, warm periods must have been long enough to thaw frozen sources of water and supply the lakes. The slowest thawing source is groundwater. We simulate the thawing and flow of groundwater in the region surrounding Gale to understand whether it could have been a significant source for lakes during a warm climate period. We find that it could only be significant with the most generous assumptions about flow speed and aquifer recharge. Even with generous assumptions, tens of thousands of years are required to thaw enough groundwater to have an impact on large lakes. After long enough, though, the ground would thaw entirely, possibly enabling a higher rate of groundwater delivery. Key Points: Tens of thousands of years are likely required to generate significant groundwater flow to Gale Crater with a thawing crustSurface water would likely be the dominant source for Gale lakes at the beginning of a warm episodeDeep aquifers may have played a role later on if complete thaw occurred beneath Gale [ABSTRACT FROM AUTHOR]