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IceBridge Blues

IceBridge Blues

NASA’s Operation IceBridge—an airborne mission to map polar ice—recently made some flights out of the McMurdo and Amundsen-Scott South Pole stations, giving researchers greater access to the interior of the icy continent. The flights over Antarctica (the ninth year in a row) have turned up ample science data, as well as some spectacular images.

The top photograph was acquired during a flight from McMurdo Station aboard a Basler aircraft on November 30, 2017. It shows ice flowing from the Transantarctic Mountains, a range that runs the length of the continent and separates West Antarctica and East Antarctica. The dark blue areas are where melt water—spurred by days of abundant sunshine and light winds—has flowed down into lower spots and then refroze. Refrozen melt ponds fill almost every ripple in the top-middle of the image, and along the direction of flow of the glacier visible in the foreground.

Paler blue areas indicate places where uncompressed snow has blown away to reveal blue ice. Ice is generally blue for the same reason that water is blue. Namely, the bond between oxygen and hydrogen atoms in the water molecule, frozen or liquid, absorbs longer wavelengths of visible light and leaves behind the shorter (blue) wavelengths. Dense glacial ice that has been compressed and the air bubbles are squeezed out will appear even bluer.

The second photograph, acquired on November 29 during a flight to Victoria Land, shows an iceberg floating in McMurdo Sound. The part of the iceberg below water appears bluest primarily due to blue light from the water in the Sound.

The undersides of some icebergs can be eroded away, exposing older, denser, and incredibly blue ice. Erosion can change an iceberg’s shape and cause it to flip, bringing the sculpted blue ice above the water’s surface. The unique step-like shape of this berg—compared to the tabular and more stable berg in the top-right of the image—suggests that it likely rotated sometime after calving.

This iceberg shows just a hint of blue color on its surface where snow has been removed. Snow and ice that appears white will contain large numbers of air pockets, bubbles, and other reflective particles that tend to reflect all wavelengths of visible light equally.

Photos courtesy of Chris Larsen, NASA's Operation IceBridge mission. Story by Kathryn Hansen.