Percolation threshold for vertical fluid flow through granular sea ice

The fluid permeability of sea ice governs a broad range of physical and biological processes in the polar marine environment, such as melt pond evolution, snow-ice formation, and nutrient replenishment for sea ice algae. Columnar sea ice is effectively impermeable to bulk flow for brine volume fractions below about 5%, while above this threshold fluid can flow vertically through the ice. Granular sea ice has different crystallographic and brine microstructures. It has long formed a significant portion of the Antarctic sea ice cover, and has become increasingly prevalent in the rapidly changing Arctic. Data gathered off the coast of East Antarctica indicate that this threshold for bulk vertical flow through granular sea ice there is around 10%. While columnar and granular microstructures display quite different threshold values, percolation theory predicts that they have the same universal critical exponent for the permeability as a function of porosity above the threshold, which agrees closely with our data. These findings impact physical and ecological modeling efforts, and must be taken into account when granular ice is present.