Editing Antarctic krill (section)

== Geographic distribution ==
[[File:krilldistribution.jpg|thumb|Krill distribution on a [[NASA]] [[SeaWIFS]] image&nbsp;– the main concentrations are in the [[Scotia Sea]] at the [[Antarctic Peninsula]]]]
Antarctic krill has a circumpolar distribution, being found throughout the [[Southern Ocean]], and as far north as the [[Antarctic Convergence]].<ref name="MSIP">{{cite web |title=''Euphausia superba'' |website=Euphausiids of the World Ocean |publisher=Marine Species Identification Portal |access-date=May 20, 2011 |url=http://species-identification.org/species.php?species_group=euphausiids&id=43}}</ref> At the Antarctic Convergence, the cold Antarctic surface water submerges below the warmer [[subantarctic]] waters. This front runs roughly at [[55th parallel south|55° south]]; from there to the continent, the Southern Ocean covers 32 million square kilometres. 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 {{convert|24000000|km2}} become ice free in summer. The water temperature fluctuates at {{convert|-1.3|-|3|C|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 [[eddy (fluid dynamics)|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.<ref>Hoare, Ben (2009). Animal Migration. London: Natural History Museum. p. 107. {{ISBN|978-0-565-09243-6}}.</ref> One swarm covered an area of {{convert|450|km2|mi2|abbr=off|sp=us}} of ocean, to a depth of {{convert|200|m|ft|abbr=off|sp=us}} and was estimated to contain over 2 million tons of krill.<ref name="Hoare, Ben 2009 p. 107">Hoare, Ben (2009). Animal Migration. London: Natural History Museum. p. 107. {{ISBN|978-0-565-09243-6}}</ref> Recent research suggests that krill do not simply drift passively in these currents but actually modify them.<ref name="Hoare, Ben 2009 p. 107"/> By moving vertically through the ocean on a 12-hour cycle, the swarms play a major part in mixing deeper, nutrient-rich water with nutrient-poor water at the surface.<ref name="Hoare, Ben 2009 p. 107"/>