Permafrost is soil that remains frozen for at least two years, with a thin active layer on top that thaws during summer. Some permafrost layers are hundreds of thousands of years old, making them a natural archive of past climate, microbial life, and biogeochemical processes.
(Williams et al. 2025, Trends in Microbiology)
Scientists often drill permafrost cores to study these ancient layers and the life they harbor. Within permafrost, there are unusual pockets of unfrozen, highly saline water called cryopegs. These brine layers form when freezing in the surrounding soil pushes out salts and other dissolved solids, which accumulate in the trapped water, creating highly saline liquid habitats. Typical cryopegs are two to three times as salty as seawater, with salt concentrations of 70-120 grams per liter. This high salinity keeps the water liquid even below the normal freezing point, down to about -10°C or lower.
Despite the extreme cold and high salinity, cryopegs are far from sterile. Microorganisms, known as extremophiles, survive and carry out metabolic processes in conditions that would kill most other life. These extreme habitats offer insights into the limits of life on Earth and resemble conditions on ice-covered moons, making them fascinating models for astrobiology.
Cryopegs also have implications for climate change. As permafrost thaws, microbial activity releases greenhouse gases like carbon dioxide and methane, accelerating global warming. Studying how microbes survive in cryopegs helps scientists predict how these frozen ecosystems will respond to rising temperatures.
These liquid pockets reveal the remarkable resilience of life, offering insights into Earth’s hidden ecosystems and the potential for life beyond our planet.
Léa Zinsli, PolarJournal