Preferred crystal orientation in fresh water ice

Crystal orientations in lake ice have been the subject of considerable attention due to their influence on albedo and stability during the melt season. It has been reported in the literature that ice sheets on freshwater bodies develop preferred crystal orientations. In some ice sheets c-axis vertical crystals become dominant, in others, c-axis horizontal dominate. However, the reasons for these differences are unclear, and it has been suggested that the preferred orientation depends either on the thermal characteristics of the water body or on whether the ice is seeded. The experiments presented here confirm that in seeded fresh water ice sheets the favored c-axis orientation is horizontal, regardless of the bulk temperature gradient in the water column. However, these experiments also suggest that the temperature gradient close to the interface is influenced by seeding. We propose that the partial melting of seeds prior to freezing of seeded ice sheets creates conditions favorable to the growth of c-axis horizontal crystals. Alternatively unseeded ice sheets, grown under the same conditions, develop a preference for c-axis vertical crystals.