Difference between revisions of "Antarctic krill"

Antarctic krill have a circumpolar distribution, being found throughout the [[Southern Ocean]], and as far north as the [[Antarctic Convergence]]. At the Antarctic Convergence, the cold Antarctic surface water submerges below the warmer subantarctic waters. This front runs roughly at 55° south; from there to the continent, the Southern Ocean covers 32 million square kilometers. This is 65 times the size of the North Sea. In the winter season, more than three-quarters of this area become covered by ice, whereas 24,000,000 km2 become ice free in summer. The water temperature fluctuates at -1.3 C (3 F).

The waters of the Southern Ocean form a system of currents. Whenever there is a [[Antarctic Circumpolar Current|West Wind Drift]], the surface strata travels around Antarctica in an easterly direction. Near the continent, the [[Antarctic Coastal Current|East Wind Drift]] runs counterclockwise. At the front between both, large eddies develop, for example, in the [[Weddell Sea]]. The krill swarms swim with these water masses, to establish one single stock all around Antarctica, with gene exchange over the whole area. Currently, there is little knowledge of the precise migration patterns since individual krill cannot yet be tagged to track their movements. The largest shoals are visible from space and can be tracked by satellite. One swarm covered an area of 450 km2 of ocean, to a depth of 200 m and was estimated to contain over 2 million tons of krill. Recent research suggests that krill do not simply drift passively in these currents but actually modify them.