Modelling the liquid-water vein system within polar ice sheets as a potential microbial habitat

Based on the fundamental and distinctive physical properties of polycrystalline ice Ih, the chemical and temperature profiles within the polar ice sheets, and the observed selective partitioning of bacteria into liquid water filled veins in the ice, we consider the possibility that microbial life could survive and be sustained within glacial systems. Here, we present a set of modelled vertical profiles of vein diameter, vein chemical concentration, and vein water volume variability across a range of polar ice sheets using their ice core chemical profiles. A sensitivity analysis of VeinsInIce1.0, the numerical model used in this study shows that the ice grain size and the local borehole temperature are the most significant factors that influence the intergranular liquid vein size and the amount of freeze-concentrated impurities partitioned into the veins respectively. Model results estimate the concentration and characteristics of the chemical broth in the veins to be a potential extremophilic microbial medium. The vein sizes are estimated to vary between 0.3 μm to 8 μm across the vertical length of many polar ice sheets and they may contain up to 2 μL of liquid water per litre of solid ice. The results suggest that these veins in polar ice sheets could accommodate populations of psychrophilic and hyperacidophilic ultra-small bacteria and in some regions even support the habitation of unicellular eukaryotes. This highlights the importance of understanding the potential impact of englacial microbial metabolism on polar ice core chemical profiles and provides a model for similar extreme habitats elsewhere in the universe.

► Intergranular liquid vein systems in polycrystalline ice of polar ice sheets as microbial habitat. ► Grain size and borehole temperature mainly determine aqueous vein chemistry and vein diameter. ► Veins are hyper acidic and the modelled vein diameter ranges between 0.3 and 8 μm. ► Possible microbial metabolism in veins may affect inorganic ionic profiles from polar ice cores. ► Model provides a prototype for exploring similar icy extra-terrestrial habitats.