Significance Freezing and melting of ice are one of the most common events on Earth. The dynamics of ice crystallization are relevant to climate research, mitigating frost damage in agriculture and construction, glacier dynamics, tissue and food preservation, and transportation. We describe the use of microfluidic devices, accompanied by precise temperature control, to examine the effect of H/D isotope exchange between liquid light water and solid heavy water on ice growth dynamics. These studies revealed unusual morphologies at the ice surface in contact with the liquid, including curious unsteady morphological features that give the appearance of oscillation due to complex interplay of H/D exchange, thermal gradients, and local surface curvature.