L'Antàrtida: un continent únic

Abstract

For the major part of people that visit the Antarctic, it is one of the most beautiful places on earth. Its gigantic icebergs, ice shelves, peculiar fauna, and exceptional environmental conditions are found nowhere else on the globe. The rock and permanent ice of the Antarctic landmass cover about 14 millions km2. If the ice melted, Antarctica would consist of the East Antarctic continent and the archipelago of West Antarctic leading northward to the Antarctic Peninsula. The winter sea ice roughly doubles the effective area of Antarctica. At its deepest point, the dome of the polar ice sheet is 4800 meters while the South Pole stands on 2.8 km of the ice. During the last decades the studies on both the sea ice zone and the water column have undergone profound changes as to the appreciation of these subsystems in terms of their quality and productivity. The sea ice is no longer considered as a hostile environment devoid of life except for a few warm-blooded animals which rest or reproduce on it, on the contrary: we now know that the sea ice maintains in its crevices and channels, and under its lower surface, an abundant life, rich in biomass, perfectly adapted to high salinities and low temperatures, and even revealing a certain diversity. The water column is not characterised by a generally high primary productivity as was thought two decades ago, but is rather an oligotrophic retention system that is dominated by small microalgae and protozooplankton, in which the blooms of the large diatoms are restricted principally to the Polar Front and neritic areas. On the other hand, many recent studies on the communities located on the sea floor, seem to confirm the image of an essentially complex, often diverse, system with a largely endemic fauna characterised by retarded life strategies which are adapted to the polar environment. The degree of coupling of the benthic fauna to the highly seasonal primary production is very close in some groups but quite contrary in others. This may reflect the consequences of recent glacial periods which caused a frequent shift on the continental ice edge combined with changes in sea ice cover