The Salty Science of Brinicle Formation: Impact of Salt Composition on Brinicle Growth and Morphology

Abstract

Brinicles are hollow ice structures that grow under sea ice. These structures form when supercooled brine is released into the surrounding ocean, causing ice to form around it. These structures have recently garnered interest for their possible existence on the ocean moons of Enceladus and Europa. This work investigated the impacts of specific salt compositions on brinicle growth and morphology. Brinicles were grown in a subzero facility for 2 h with four different brine solutions: sodium chloride (NaCl), calcium chloride (CaCl2), Enceladus analog containing NaCl (henceforth labeled as “ENC”), and a Don Juan Pond analog containing CaCl2 (henceforth labeled as “DJP”) utilizing elemental chemistry data from Don Juan Pond (Wright Valley, South Fork, Victoria Land, Antarctica). The brinicles were imaged during growth and extracted for analysis of ice grain size and inner column dimensions. This research concludes that varying salt compositions had a significant impact on the growth, stability, and morphology of brinicle formation. The CaCl2-based solutions resulted in brinicles that were more diverse and structurally complex than those grown in NaCl-based solutions, potentially driven by differences in heat capacities and solute properties. This investigation highlights how salt composition influences the physical characteristics of the brinicle, impacting the microenvironments in and around the brinicle and thus affecting their potential habitability in both terrestrial and extraterrestrial frozen environments. The salinity and rapid formation of brinicles would allow for the capture and entombment of halophilic microorganisms. While the stability of organics and biogenic products is not explored in this study, this investigation sets the stage for where and why these frozen water features should be a priority target for future astrobiological and geomicrobiological studies.