ARK-XXVI/3, Weekly Report No. 7

At the beginning of last week, we left the ice-covered portion of our journey and started the last part of our station program in the entirely ice-free Laptev Sea. After weeks of irregular noises from thick ice floes banging against the hull of the ship, it became quiet and we were welcomed by the smooth rolling of waves. Last time we were here during an expedition in September 2007, new ice formation had just started. This year the water temperature, measured regularly at the keel, was above 3°C, i.e. 5 degrees above the temperature which we had encountered in the central Arctic. Here in the Laptev Sea, insolation has heated the ice-free water surface over the summer and there is no sign of ice formation occurring anytime soon.

Now the question is – was there stronger melting this summer? In addition to a reduction in sea ice extent, did sea ice also become thinner? This important question is tackled by the group of sea ice physicists. The volume of sea ice loss is a function of area and thickness.  The area of the sea ice cover has been determined very reliably from satellites observation for several decades. These observations show a significant shrinking of the summer sea ice, but do not provide any insight into ice thickness.

Since the helicopter has to fly far away from the ship and fly long distances at very low height, the weather conditions must be favorable. Before each flight we rely on the Polarstern meteorological office for accurate weather predictions. For an EM-bird flight the visibility must be at least 5 km and the clouds must not be lower than 300 m. Unfortunately, these conditions were only rarely met which meant that we had several days without EM-bird flight.

In total, we had 16 days where the weather was suitable for the sea ice physicists to carry their observations from the helicopter. Measurements were performed in various regions over a total distance of 2500 km. After each a flight, the scientists perform a statistical analysis of their most recent observations. First-year ice, which has formed last winter, and multiyear ice, which has survived the last summer and thus is much thicker, are easy to distinguish. In the past decades, the central Arctic was mostly covered by older, hence thicker ice. Satellite observations which allow to tell old and new ice apart based on sea ice roughness indicate a recent trend towards younger ice. In fact, the scientists found mostly first-year ice during our cruise and could now determine its thickness. Only in the Canadian Basin and close to Severnaya Zemlya notable amounts of thick multiyear ice were found.