ARK XXII/2, Weekly Report No. 6
3 - 10 September 2007
While the week before last brought us to our northernmost station, during the last week we passed the data border at 180° East and reached our easternmost position at 135° West. In this region it was not always easy to tell our heading. To go from 175° East to 175° West one has to head eastward. Stereographic maps make it even more confusing. At mean latitudes we are accustomed to Mercator projection that shows west to the left, north to the top, etc. However, in the vicinity of the North Pole, we use maps with stereographic projection where the latitudes are circles around the North Pole. In this case, to describe a southeast heading toward western longitudes we point up left on our map, which requires some mental exercises.
Early last week the first half of our long cruise was over! On Sunday a long ice station was on the schedule and we took the opportunity to celebrate our first very successful Halftime with a Glühwein on ice. This was accompanied by a soccer game, Germany against Netherlands (both mixed with other nations). At minus 2 deg C the game was played, for some minutes at least, in short trousers. After a finish with 4:2 for Germany, the game was followed by skating on the smooth, frozen melt ponds. This was of course the domain of the Dutch colleagues. In between even the sun won against the everlasting grey clouds and for some hours shone a milky friendly light over the ship and the floe which made both very photogenic. Everybody returned onboard refreshed and exhausted.
Besides Punsch and soccer, research was also conducted on the floe by sea ice biologists, physicists and oceanographers. In contrary to fresh water ice, sea ice contains a network of fine channels filled with high salinity brine because the ice crystals do not incorporate salt. These channels form a suitable habitat for a very specialized ecosystem. To some extent the channel system provides protection against predators. On the other hand, a variety of challenges have to be faced by the organisms: very low temperatures, extremely variable salinities that expose cells to osmotic pressure, and last but not least, in summer the comfortable niche melts away completely. So far, sufficient multi-year ice – which survives the winter together with its inhabitants – might provide the baseline for the growth of organisms in newly formed ice. If the tendency continues towards ice-free summers – like the drastically low ice coverage observed this summer – this ecosystem may become extinct. But as long as it continues to exist, sea ice biologists from the University of Kiel try to understand more about the composition and diversity of the poorly investigated fauna in the ice. During ice stations they drill ice cores which are cut into slices to study who is living with whom in which floor under which circumstances. Some animals are collected for feeding experiments. The opportunists living immediately below the ice, which wait for food falling or creeping out from under the ice, are studied with an underwater video system.
The temperature was markedly below zero last week and with the start of ice formation the ice physics group from Hamburg University changed their focus from investigating optical properties of melt pond surfaces to the study of new ice formation. In the prevailing calm weather, new ice has grown with a fairly even surface to 5 to 10 cm thick, called dark or light “Nilas”. In contrast to fresh water ice, the salt content in seawater causes irregularities of centimetre size at the surface of the sea ice, causing some roughness on the ice surface. To measure the roughness of the Nilas the members of the ice physics group lay, stuffed into survival suits, on their stomach at the edge of the floe and work with a kind of ruler. Afterwards they mark their measurement locations with blue garbage bags and fly over them in the helicopter, taking a survey of the roughness with a scatterometer at different frequencies and polarisation angles. Sophisticated algorithms are used to combine the results of the flight measurements with the ruler measurements. An observation was that frost flowers are able to form at -8°C, and not only at lower temperatures as was believed before.
Apart from the biological and the ice-physical work the “halftime” floe was used to deploy the first oceanographic buoy. To obtain ocean measurements throughout the year, the researchers installed a platform on the ice from which a CTD system can profile to 1000 m depth to record temperature and salinity once per day – just as we do it from the ship. The Ice-Tethered Profiler will drift with the floe across the Arctic Ocean together with a widespread array of similar oceanographic platforms that are launched in an international collaboration during IPY 2007/08. In this way we will obtain for the first time a multi-year year-round pan-Arctic hydrographic survey.
The possibility for continuously adapting the short- and long-term planning of the cruise programme to the sea ice situation requires knowledge of the large-scale conditions. Here we have to rely on land-based information. In this regard we have the additional problem that our email traffic is very restricted so that sending huge files with detailed ice information is impossible. Therefore we are very grateful to Lars Kaleschke and his group from Hamburg University who have provided us all along the cruise, weekends included, with minimal sized files carrying maximal information.
Best regards in the name of all participants,