Turbulent Enhancement of Melting Ice Spheres

Models underpredict ice loss of submerged glaciers in polar regions. A major source of uncertainty is the effect of turbulence on melting. Turbulence continually stirs cold meltwater immediately adjacent to the ice with relatively warmer or saline ambient fluid in the environment, promoting more efficient melting. However, the mechanism by which turbulence, when coupled with ambient salinity and temperature, increases melt rates is still unknown. To understand the fundamental physics by which turbulence and temperature affect melting rates, we designed an experimental study that allows us to explore melting of a submerged ice sphere in a freshwater tank. We performed a baseline study with quiescent ambient water ranging in temperature from 2 to 10 degrees Celsius to explore the flow of convective currents. In subsequent tests, we performed experiments in homogeneous isotropic turbulence absent mean flow using a custom-designed apparatus at three different levels of turbulent kinetic energy, across the same temperature range. We use particle image velocimetry (PIV) to measure the velocity field and turbulence statistics of the ambient water and meltwater to study the unique boundary layer flows that develop. We also use PIV data to measure ice loss in time. We present a full quantification of melting across a wide parameter space exploring contributions from ambient turbulence and temperature in a zero mean shear environment. These experiments allow us to quantified key uncertain parameters that will improve models of glacier melting.