Freshly calved icebergs from Sermeq Kujalleq in Kangia, Greenland: is their blue ice temperate?

Abstract. Blue ice on the freshly calved icebergs from Sermeq Kujalleq in Kangia, Greenland, is a striking feature which is currently barely understood. Its extent and properties provide important insights into the flow dynamics of this polar ice stream, since it occupies the bottom-most quarter of the total ice thickness, and it has been conjectured that the blue ice is temperate. Here, we document the phenomenon with ground-based time-lapse camera images, theodolite measurements, thermal imagery, and multi-spectral satellite imaging from Sentinel-2. The blue ice shows intriguing properties as its reflectance spectrum stands out from other types of ice and resembles that of water. The blue ice whitens under the action of solar radiation, potentially caused by the drainage of liquid water, which would indicate temperate conditions. Thermal imaging on the other hand refutes this interpretation, indicating that blue ice is colder than white ice when using a standard thermal emissivity. Freshly calved icebergs offer a unique opportunity to explore properties and structures (layering, folding) of ice which are formed at great depth within polar ice streams.