The Sea Ice Physics Team – From basic tools to advanced technology

Quelle: 24 June 2015
A. Fong, M. Kędra, and C. Mӓrz
For many people (including members of this blog team), remembering their physics lessons at school is not a very fond memory. Physics, often coupled with math, all too often seems very abstract. On a polar expedition, however, the physicists are a far cry from the stereotypical image of a theoretical physicist - sitting in front of a computer crunching highly complex equations. The members of the sea ice physics team are zipping up their survival suits, packing Nansen sledges full of heavy equipment, and starting up the Skidoos. They use tools as basic as wooden sticks and as advanced as underwater robots. They employ the coolest-looking technology on this expedition. Somewhat surprisingly, the physics they do is not just brainy, but very physical and applicable. One of the most critical services the team provides for the expedition are photogrammetric flight surveys of ice floes surrounding the Polarstern. These surveys are fundamental to their scientific objectives and for ground-truthing satellite-derived sea ice maps. They also serve as a way of seeing the path forward towards our next station. With limited visibility from the ship, the aerial surveys by the sea ice physics and helicopter teams provide real-time information about everyday changing ice conditions. The teams work closely with the captain, chief scientist, and crew to determine the best route through the ice. The sea ice physicists focus on measuring and comparing the thickness and distribution of sea ice and snow cover by a range of analytical tools. These tools range from remote sensors on satellites to electromagnetic devices hanging down from a helicopter, to sticks stuck into the snow. The variety of tools used cover a wide range of scales, which allow for quantitatively and qualitatively examining properties of ice. The Electromagnetic (EM) Bird looks a bit like a torpedo, but is instead filled with various sensors measuring the thickness and roughness of the sea ice along extended transects. Broad mapping of ice floes can be accomplished using the EM bird. On the ice floe, they use a Remotely Operated Vehicle (ROV), a diving robot hanging on a cable that can be flown directly underneath the ice, steered from a little control hut on the ice (lovingly named 'Bockwurstbude'). It produces great pictures and movies under the sea ice, which displays a lot more structure and relief than one would think. At the same time, upward-pointing sensors measure the amount of sunlight that penetrates through the ice, which is subject to large variations depending on ice and snow thickness. Nonetheless, making holes in the ice using a quick drill and measuring snow properties like depth, temperature and grain sizes remain the most straightforward methods to complement the physical perspective of sea ice cover. Taken together, and following complex analyses, all these data sets gathered over many years provide the evidence for an overall retreat of Arctic sea ice. These observations and findings are critical to informing the global climate change debate.