A zodiac tour took us right past some incredible, blue shimmering ice sculptures. One even displayed two different kinds of intense blue colors I had not seen before. It was hard to believe it was real yet the darker hue immediately reminded me of my beloved deep blue Sapphire ring. This moment — seeing these remarkable colors in between all the white — will stay with me for a long time. It’s something that I didn’t know was on my bucket list but I’m delighted that I checked it off. At other times, we saw enormous crevasses in the tall mountains surrounding us. They, too, revealed dark blue ice underneath the white, snow-covered layers.
So why is the ice in Antarctica blue? The biggest clue comes from its age: the Antarctic ice is thousands of years old! As snow falls in cold weather, it accumulates, layer upon layer. Over time, the snow compacts more and more, turning into ice. This way, the fluffy and light snow is turned into hard and very compact glacial ice with very little air in it. It’s so compacted, it looks like polished glass, glistening in the sun.
Unlike white snow, which reflects all colors of light due to its predominantly air-filled composition (air bubbles scatter light with all wavelengths), compressed ice takes on a different character. When the air is significantly reduced, the ice develops a hexagonal crystal structure. This structure selectively absorbs red light with longer wavelengths while scattering the blue light with shorter wavelengths — it looks blue. This behavior does, in fact, closely resemble that of the optical properties of a Sapphire gemstone.
Let’s “look” at icebergs some more. Only 10% of their mass is above the surface. What we see there is typically covered in snow, protecting the underlying ancient ice from view and temperature fluctuations. That is not the case for the 90% of the iceberg in the water. The more recently formed ice layers have been washed away, thus revealing older and older ice that will become progressively bluer. With the water being so crystal clear, it is possible to see the blue ice shimmering through from down below. This makes every iceberg appear to sit in the middle of an intensely blue-green area.
What happens if the ice under water has melted? The iceberg will turn over in one massive tumble. This reveals the most bizarre and beautiful shapes and structure that had formed underwater during the melting process. As such, it’s not difficult to identify those icebergs who are on their second life. First timers have rough, even sharp, edges and are often very “blocky” since they broke off from larger ice shelfs. The reborn ones are round, show structure with holes and grooves, and have less snow on. They are also shiny and blue, as they reveal their thousand year old ice freely and easily.