THE MCMURDO DRY VALLEY LAKES, ANTARCTICA, AS ANALOGS FOR MARS LAKES OF THE PAST

The McMurdo Dry Valleys in east Antarctica is one of the coldest and driest regions on earth, and yet hosts a viable microbial ecosystem in local soils, streams and lakes. The perennially ice-covered lakes are the most productive habitats in the region and have long been used as analogs for purported past lakes on Mars. The thick ice covers thermally buffer the liquid water underneath, allowing for a year-round aquatic habitat in this harsh environment. Lakes exist in all the major dry valleys, which range in mean annual temperature from around -18 to -19°C (Taylor and Wright Valleys) to -27°C (Victoria Valley). The colder temperatures in Victoria Valley have allowed for the formation of the thick (>27 m) ice cover on Lake Vida compared to the relatively thin (4-6 m) ice covers in the other valleys. Lake Vida also contains a viable microbial ecosystem in brine-laden ice below 16 m, but unlike the other lakes, this ecosystem has no connection to the surface. This succession of colder temperatures and more deeply ice-covered lakes across the dry valleys could be considered a model for what happened as the martian climate cooled from the Noachian to the Amazonian. Summers in Victoria Valley remain warm enough for glacial melt from valley glaciers to occasionally flood and refresh the ice surface, but if temperatures cooled to the point this did not happen, Lake Vida would start sublimating and form a lag deposit on its surface and accumulate aeolian sands and fine gravels to eventually bury the ice and encased brine. Such phenomena can collectively inform at least three key geologic contexts on Mars: (1) englacial habitability of mantled metastable ice sheets in the mid latitudes; (2) pro- and peri- glacial geology, including pedogenesis and hydrology; and (3) metastability of any polar subglacial aquifers.