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ISPOL-Logbook4: 16 - 17 November, 2004

erstellt von redaktion zuletzt verändert: 23.08.2007 15:29

For most people snow and ice is something that causes seasonal problems in wintertime. But from a more sophisticated viewpoint the various forms of frozen water shape a multi dimensional world that is largely unknown. Honestly, one should consider to speak of SNOWS and ICES rather that snow and ice.

For all the experts on Polarstern this is far from being brand new, but even basic knowledge can be extended. That is why the 1000 miles ahead, to Polarstern's final destination is also used to lay a transect through this icy world. The floes are measured to obtain figures concerning thickness, condition (age), and snow coverage. Educated guess and a good sense of systematics are needed. And this is how it works: Well-trained experts spot ice floes from high above (from the bridge) every hour - at night every two hours. It is very helpful that the vessel causes pieces of floe to tumble while crushing them, so their thickness is clearly seen from the bridge. A red and white measuring stick protruding out from the ship helps to calculate the dimensions from 20 meters above. The facts and figures are continuously correlated to the current position of Polarstern. Before starting their survey, the "floe counters" make sure that all of them have about the same scales when it comes to draw quick decisions. For example the teams have to decide whether they have spotted Frazil-Ice (delicate icy crystals drifting in smooth water) or so called "Nilas" (thin layers of ice that grow in still waters). All in all there are 14 different types of ice to be distinguished - from very thin to "younger grey" ending with "fast ice". Moreover, the floe size plays a major role; there are tiny patches of so-called pancake ice on one end of the scale and giant floes of 2 km in diameter at the other end. The topography is another item - from "level ice" to "old and weathered". Those, which bear ridges and bolder-like structures, are survivors of the last Antarctic summer. And last but not least the patches, leads, and strips of ice-free water have to be measured. This system was developed by Tony Worby from Australia - one of ISPOL's ice experts on this trip.

Christian Haas is about to make an ice-"echo-sounder" work that is fastened in front of Polarstern's ice breaking bow and will hopefully deliver a constant flow of data on ice thickness and coverage of the Weddell Sea.

Ice has many admirers. The sea ice-biologists fancy the dark green (sometimes brown) bottom layers teeming with floral and faunistic life. There are plenty of questions to be solved. How on earth can living creatures survive such unfavourable conditions like darkness (due to seasonal snow coverage of floes), cold and high salinity in the brines - the salty icy canals in the floes? Could it be that DOM (Dissolved Organic Matter) spread all over the oceans is derived mainly from ice algae around Antarctica? And does UV-light reach the upper part of the water column in spite of snow coverage in Antarctic winters.

Polarstern is on a pirate's mission. Her prey lives in a world apart, but the clue might well be: the results of this trip could possibly contribute to questions also vital for comparatively moderate zones.

Claus-Peter Lieckfeld