Anomalous Convective Flows Carve Pinnacles and Scallops in Melting Ice

We report on the shape dynamics of ice suspended in cold fresh water and subject to the natural convective flows generated during melting. Experiments reveal shape motifs for increasing far-field temperature: Sharp pinnacles directed downward at low temperatures, scalloped waves for intermediate temperatures between 5 degrees C and 7 degrees C, and upward pointing pinnacles at higher temperatures. Phase-field simulations reproduce these morphologies, which are closely linked to the anomalous density-temperature profile of liquid water. Boundary layer flows yield pinnacles that sharpen with accelerating growth of tip curvature while scallops emerge from a Kelvin-Helmholtz-like instability caused by counterflowing currents that roll up to form vortex arrays. By linking the molecular-scale effects underlying water's density anomaly to the macroscale flows that imprint the surface, these results show that the morphology of melted ice is a sensitive indicator of ambient temperature.

Automated summary

We investigated the shape dynamics of ice in cold fresh water during the melting process. Experimental and phase-field simulation results showed that as the cooling rate increased, the shape of the ice changed from downward sharp pinnacles, to scalloped waves at intermediate temperatures, and finally to upward pointing pinnacles at higher temperatures. These shape changes were closely linked to the density-temperature profile of water.