Field measurements of Arctic grease ice properties and processes

In situ measurements of grease ice from fjords on Svalbard reveal new basic properties of the surface ice cover. New ice formation often takes place as growing frazil crystals in a surface layer of grease ice. A method for sampling grease ice is described. The grease ice layer is found to be as thick as 70 cm in places, but many of the measurements are around 10 cm. Salinity of the bulk grease ice is around 25 psu, while the drained grease has salinity around 20 psu. The grease ice congeals into a solid ice cover depending on surface cooling. Ice concentration is calculated based on the measured salinity and is around 25% for the grease, and above 60% for the new solid ice. Grease ice, or frazil ice crystals, forms in response to atmospheric and oceanographic forcing, and the salt released by the ice growth influences local hydrography. For the Storfjorden polynya, existing parameterizations for grease ice thickness in relation to wind speed are discussed. The changing wind conditions during the fieldwork partly explain the deviation from an idealized situation, but tidally driven turbulence and the effects of snow drift are suggested as important processes to include in future theoretical descriptions of grease ice processes.