About two and half weeks ago the Alfred Wegener Institute for Polar and Marine Research (AWI) issued a press release to inform us of the fact that their research vessel and icebreaker Polarstern had arrived at the North Pole. In the blog post I dedicated to this news, I mentioned a snippet about their findings concerning ice thickness. I have finally come around to read a bit more on AWI's excellent Polarstern Blog, and have translated some more snippets about ice thickness. All the images come from the Polarstern Blog as well.
Schollensuche richtung Nordpol
the search for ice floes on the way to the North Pole
In order to document the ice conditions during our journey we observe the sea ice on an hourly basis. The ice conditions are logged following an international standard. Ice cover, type, thickness and the distribution and amount of melt ponds are recorded and documented with photographs. Ice thickness is estimated with a yardstick aboard the ship by observing the broken ice floes that are standing upright.
The first results from our observations show that the sea ice is relatively thin, young and unstable. Older multiyear ice, which used to be typical for this region in the past decades, makes up just 10 to 20% of the observed ice. Consequently we can travel and navigate through the ice much quicker than in the past, and do not get stuck. On top of that the journey is made easier by many stretches of open water which allow us to travel at a speed of 3 to 6 knots (5 to 10 km/h) from one measuring point to the other. This gives us more time for operating our ice and water stations.
The downside of this thin, young and unstable ice is that it's difficult to find appropriate ice floes for our operations on the ice. Most of the ice floes are too small and unsuitable, which means we are often searching for hours. Sometimes an ice floe breaks up when we try to moor, and we have to try another time. Coupled with the time it takes to get attached to the ice the search can take several hours. Quite a paradoxal situation, as we are in the middle of the icy Arctic, near the North Pole.
Thickness profile of first year ice that was measured by an electromagnetic sonde on August 16th 2011. Most of the ice is 1 m thick, with here and there a pressure ridge that's over 3 m thick (image courtesy of Stefan Hendricks, Alfred Wegener Institute)
Eisdickenmessungen aus der Luft
aerial ice thickness measurements
Two helicopters are used to measure the sea ice thickness along our route and observe the ice surface. As we have been doing this since 2001, we have a good idea of how sea ice thickness has developed in the past decade. The measurements have a very high data density. This data is especially interesting in summer, when satellites have a hard time measuring the ice thickness due to melt ponds.
We measure the sea ice thickness from the sky with the so-called EM-Bird, which is suspended 20 m below the helicopter. Because sea ice has a much lower electrical conductivity than sea water, the thickness of the sea ice can be determined by measuring electromagnetic fields.
Helicopter with EM-Bird (image courtesy of Mario Hoppmann, Alfred Wegener Institute)
Through a profile we can determine the amount of first year ice and multiyear ice. First year ice consists of flat ice floes with a lot of melt ponds on them. Multiyear ice is significantly thicker than first year ice and can be easily recognized by its irregular shape.
For these measurements we make two-hour triangular flights with a side length of 40 miles (74 km). One person in the helicopter operates the EM-Bird and is responsible for checking its height. This person is in radio contact with the pilot and keeps him briefed on the height of the EM-Bird, which ideally should be between 10 and 15 m.
We regularly rise to a height of 130 m to make a measurement without interference from the sea water and calibrate the system. These zero measurements are necessary to be able to ascertain the ice thickness down to a precision of 10 cm.
A second person in the helicopter makes a photograph every two minutes with a camera with built-in GPS to document ice conditions along the profile. Both abovementioned ice types can be observed, although this year we mainly encountered first year ice with a thickness of approximately 1 meter.
As a bonus I have found a cool video on Youtube showing the EM-Bird in action:
I would like to thank the Alfred Wegener Institute for Polar and Marine Research for doing this research and maintaining an excellent blog to engage the general public.
I translated really fast, but it should be slightly better than Google Translate. :-)