Ice-barrier

The ice-barrier is an extent of cold Mer. It is formed during the polar Hiver , when the temperature of sea water goes down in lower part from -1,9°C. In the middle of the winter, the thickness of Glace can reach 1,5 to 2 meters, without counting the snow which accumulates there.

The buoyancy of the ice-barrier is due to the difference in density between the ice and that of liquid water: the ice, less dense, undergoes the Poussée of Archimedes.

Part of the ice-barrier never melts, but one should not confuse this ice of perennial sea with the polar icecaps (Greenland, the Antarctic) which are consitituées of continental ice (Fresh water).

Formation of the ice-barrier

At the end of the summer, the arctic cold settles, sometimes brutally (- 40°C); surface of the ocean cools but because of the movements of the sea (Houle, Vague S…), the ice does not take an only one blow. When the temperature of water reached -1,8°C, the first spangles of ice crystallize then agglomerate until forming a beginning of crust on water. This one will be solidified rather quickly, but as long as it does not reach a few centimetres thickness, it remains fragile and the movements of water can fissure it. Once frozen surface, the sea water is isolated from the air and the process slows down. The ice-barrier thickens then slowly, by its lower face, until reaching approximately 2 meters. Beyond a certain thickness, the ice constitutes nothing any more but one vast block covering wide: it is the ice-barrier itself. Sea water freed of salt by freezing (" expulsion" salt towards deeper water).

During the winter, snow-covered precipitations which accumulate on its surface increase the thickness by it.

Unfasten

In the middle of the winter, the ice-barrier extends on nearly 15 million km ², of which about half will melt during the summer. When it becomes again prone to the movements of the sea, it splits up, breaks, opens, overlaps in large plates then of increasingly small pieces. These plates are frequently used for the marine mammals like the Morse S, the Phoque S or the Otarie S to take the sun there and to rest there.

The remaining part will persist 2,3,4 years or more and its thickness will reach 4 to 5 meters then. During this time, this crust of ice will cross the Icy Ocean, carried by the currents: it is the Arctic drift.

Ice-barrier and ships

The Navire S taken in the ice-barrier which is formed do not have in general an other solution only to remain on the spot and to prepare to them Hivernage. Only a ship designed to withstand the pressure exerted by the ice on its sides has good lucks resist. Such a ship has a hull forming a very tilted angle with water: when the pressure increases on the hull, instead of trying to resist it, it rises mechanically.

Certain ships are especially designed to pass through a thickness of ice (lower generally than 2 meters), they are the Brise-glace S. They can cut through a path by breaking the ice under their mass or their simple push; they are also used to open the way with other ships.

Ice-barrier and climate warming

All the data-processing climatic models predict that climate warming will more strongly touch the polar regions. In these areas, the rise in the temperature will be approximately the double of the average increase on the surface of planet. This evolution is confirmed on the ground by a recent report/ratio of NASA and National Snow and Ice Data Center (NSIDC) which reveals that the extent of the ice-barrier of the north pole forever be also reduced since more than one century.

In September 2005, the surface of the Arctic ice-barrier was of 25 % lower than that which it had on average in the years 1980. In September 2006, the extension of the ice-barrier was close to the record of 2005, without however beating it. At the date of the Saturday, September 16, 2007, there is nothing any more but 4,13 million km2 of ice which remains in the Arctic, which beats the record of 2005 (5,32 million km2) of more than 1 million km2. In general, the satellites count the surface of the ice-barrier where there is ice in concentration of 15% and more. There is only 2,92 million km2 of ice-barrier with a concentration of ice of 15% and more. It is by far the smallest surface observed by the satellites. These data are taken regularly by the NSIDC and the UIUC.

The extent of the cast iron of the ice-barrier is such as a point of no return was probably reached. Indeed, the dark water not covered with ice of the Arctic Ocean absorbs solar light well more the very reflective ice-barrier. Thus, more the ice-barrier is reduced, more the Arctic Ocean is heated quickly, thus accelerating the cast iron of the remainder of the ice-barrier and so on. This vicious circle, in scientific language a positive feedback, could lead to a total disappearance of the ice-barrier in August and September at the latest towards 2100, an unheard of situation since more than one million years. On the other hand, the majority of the models confirm that the drastic reduction in the size of the ice-barrier in summer will not be found also clearly in winter.

An additional risk of acceleration of the process of cast iron is related to the possible destabilization of the layers of hydrates of methane and of the release of ascribable to the resumption of bacterial fermentation in the tundras whose permafrost thaws out massively since the summer 2005. Certain scientists perhaps already estimate that the conditions of acceleration of the warming could become such as the majority of the estival surface of the Arctic ice-barrier could disappear even earlier, with the neighborhoods of 2025 (A. Coustou, " Ground, end of part? " , Eons editions, 2005).

If we do not act the Arctic immediately quickly will become unrecognizable , affirmed Tonje Folkestad, specialist in the climate change with the WWF. The polar bears will belong to the History, and our grandchildren will intend any to speak only in the books.

Of two years return of forwarding on board goélette Tared, the members of forwarding announced, at the end of October 2007, on the spot to have noted several proven indices of the transformations in progress in Arctic the Glacial ocean:

retreat of the ice-barrier: more than one million km2 lost between September 2005 and September 2007. The edge of the ice having moved back meanwhile of 400 km.
an increase the speed of the transpolar drift, energy of the Bering Strait to the strait of Fram, between the summer 2006 and the summer 2007. This phenomenon can contribute to the accelaration of reduction in the surface of the ice-barrier.
a progressive disappearance of the multiannual ices to the profit of the ices of the year.
the accentuated presence of cast iron plates on the surface of the ice-barrier: they cover from now on 50% of its surface in summer; as well as an increase in the rainfall between Greenland, Spitzberg and geographical north pole.

The loss of surface of the ice-barrier would currently be of 500.000 km2 per annum. Taking into account its estival surface, the ice-barrier could have completely disappeared in summer from here 8 to 10 years.

Random links: