COMBINATION OF ENVIRONMENTAL EXTREMES IN ALTIPLANIC LAKES AND THE PAST HABITABILITY OF MARS

Our project explores some the highest lakes in the world to understand the survival of habitats and life in environments that are probably the best analogs in the world to ancient martian lakes. We also characterize microbial life adaptation to extremes associated to those environments. The lakes located in the Andes are: The Licancabur lake (6,014 m), Lagunas Verde and Blanca (4,340 m). Exploration techniques include diving, geological, geophysical, hydrogeological, and biological sampling. While the impact of individual extremes on life, such as UV radiation (UVR), temperatures, and salinity is well-documented, their combined effect in nature is not well-understood when it is a fundamental issue controlling the evolution of the Habitable Zone (HZ) and that of the aqueous Habitable Zone (aHZ) within individual bodies of water. We characterize this complex interplay as a plausible model for the evolution of the aHZ in ancient martian lakes. We used ELDONET UV dosimeters, met stations, sampling, underwater temperature probes, and boat-mounted thermal sensors to characterize the physical environment. The summit lake has the highest solar radiative flux and larger daily Tair amplitude . While the three lower lakes are relicts of the same body of water, varying water temperatures, pH, alkalinity, transparency, and hydrothermal input lead to drastically different individual dynamics, impacting ecosystems. The effects on life are somewhat opposite to predictions for UVR and water column. At constant UVR, the lake with the deepest water column should provide the best protection against solar radiation. Compared to Laguna Verde (5 m), the 0.50 m deep Laguna Blanca provides less shielding to life, confirmed by a high rate of deformities in diatoms. However, the greatest abundance and biodiversity are found in Laguna Blanca, whereas Laguna Verde produces a simple and primitive foodchain. The interplay between extremes suggests that they do not always combine to generate a more hostile environment for life. In specific cases, they mitigate each other's impact, while in others, feedback mechanisms subject life to new sets of extremes. Plausibly, the same feedback mechanisms existed on Mars. Our results raise the possibility that habitability in martian lakes might, in fact, have been preserved well into declining climate conditions.