Looking into the Subsurface: A Geophysical Investigation of a Unique Set of Spotted Hypersaline Lakes in British Columbia, Canada

The search for extraterrestrial life on Mars requires an understanding of analogous terrestrial hypersaline environments and their role in biosignature preservation. The lakes of the Cariboo Plateau in British Columbia, Canada, are a series of MgSO4 dominated hypersaline lakes analogous to those hypothesized to have been present on Mars in the ancient past. These sites exhibit an enigmatic spotted appearance consisting of circular features with diameters ranging from ~1-35 m. However, the formation mechanism of the spots, or brine pools, and the thickness, depth, and lateral distribution of the subsurface salt layers of these lakeskey characteristics for understanding biosignature preservation potentialremain unknown. We completed a frequency-domain electromagnetic induction survey to generate maps of the subsurface electrical structure by traversing across the frozen lakes using a GSSI Profiler EMP-400. The measurements include a combination of subsurface signals including ice, sediment, brine, and salt that have contrasting electrical properties and generate observable anomalies. Inversion of the data using the EM4Soil software from EMTOMO additionally allowed for the creation of layered models of conductivity with depth. The data reveal the salt distribution is indeed related to spot formation yet varies between each lake. Differences in water chemistry, water level, and stage of spot development may be key factors. In several of the conductivity maps, we see low conductivity spots surrounded by high conductivity ridges, with the opposite seen in others. Additionally, we note areas of high conductivity inflow and high resistivity outflow. Inversion results of several lakes indicate vertically elongated, low conductivity structures beneath spots. Therefore, we believe our results most strongly support a formation mechanism in which the spots form from cyclical changes in climate that lead to sinking salt masses with crystals subsequently growing in layers of circular rings. Freeze-out effects may amplify this process and microbial processes may play in role localizing the salt deposition. These results will be integrated into studies of the unique geomorphology, geochemistry, and microbiology of the lakes, serving as critical information for ongoing astrobiological investigations.