Brinicles are self-assembling tubular ice membrane structures, centimeters to
meters in length, found beneath sea ice in the polar regions of Earth. We
discuss how the properties of brinicles make them of possible importance for
chemistry in cold environments-including that of life's emergence-and we
consider their formation in icy ocean world. We argue that the non-ice
composition of the ice on Europa and Enceladus will vary spatially due to
thermodynamic and mechanical properties that serve to separate and fractionate
brines and solid materials. The specifics of the composition and dynamics of
both the ice and the ocean in these worlds remain poorly constrained. We
demonstrate through calculations using FREZCHEM that sulfate likely
fractionates out of accreting ice in Europa and Enceladus, and thus that an
exogenous origin of sulfate observed on Europa's surface need not preclude
additional endogenous sulfate in Europa's ocean. We suggest that, like
hydrothermal vents on Earth, brinicles in icy ocean worlds constitute ideal
places where ecosystems of organisms might be found