Premelting controlled active matter in ice

A collection of self-propelled particles can undergo complex dynamics due to hydrodynamic and steric interactions. In the case of a foreign particle inside a subfreezing solid, such as a particle in ice, a premelted film forms around it allowing the particle to migrate under the influence of an external temperature gradient, which is a phenomenon called {\em thermal regelation}. It has recently been shown that the effect of biological impurities and their migration within an ice column can accelerate melting and migrate faster in turn. This is a positive feedback loop, where the ice melting initiates the migration of algae and diatoms, which also increases its melting. We have previously shown that the effect of regelation plays a major role in the migration of inert particles and impurities inside ice with important environmental implications. We re-cast this class of regelation phenomena in the stochastic framework of active Brownian dynamics.