Abstract: Hypersaline conditions occur in a variety of environments from evaporative ponds, salty veins within sea ice, the Great Salt Lake, and even brine pools inside the ocean. These environments are characterized by salt concentrations that range from 3x ocean salinity to saturation. In additional to high salinity these environments can challenge resident organisms with alkaline pH, high concentrations of other ions like Mg2+, and high UV flux. Despite these multiple stressors to habitability, diverse communities of halophilic algae, bacteria, and archaea populate these environments. The adaptations used by these organisms to survive and thrive have implications for understanding the limits of habitability and identifying signatures of biological activity. Today, I will present results from two ongoing projects that explore how haloarchaeal physiology induces carbonate mineral precipitation and an investigation of how microbial metabolic processes, including methanotrophy, could lead to an observed hydrogen isotope excursion in the water column of a brine pool.