Editing Antarctic Circumpolar Current (section)

==Dynamics==
The circumpolar current is driven by the strong westerly winds in the latitudes of the Southern Ocean.

[[File:thermohaline_circulation.svg|thumb|link={{filepath:thermohaline_circulation.svg}}|The ACC (red circle near the middle of the image) in relation to the global [[thermohaline circulation]] [{{filepath:thermohaline_circulation.svg}} (animation)] ]]
In latitudes where there are continents, winds blowing on light surface water can simply pile up light water against these continents. But in the Southern Ocean, the momentum imparted to the surface waters cannot be offset in this way. There are different theories on how the Circumpolar Current balances the momentum imparted by the winds. The increasing eastward momentum imparted by the winds causes water parcels to drift outward from the axis of the Earth's rotation (in other words, northward) as a result of the [[Coriolis force]]. This northward [[Ekman transport]] is balanced by a southward, pressure-driven flow below the depths of the major ridge systems. Some theories connect these flows directly, implying that there is significant upwelling of dense deep waters within the Southern Ocean, transformation of these waters into light surface waters, and a transformation of waters in the opposite direction to the north. Such theories link the magnitude of the Circumpolar Current with the global [[thermohaline circulation]], particularly the properties of the North Atlantic.

Alternatively, [[Eddy (fluid dynamics)#Mesoscale ocean eddies|ocean eddies]], the oceanic equivalent of atmospheric storms, or the large-scale meanders of the Circumpolar Current may directly transport momentum downward in the water column. This is because such flows can produce a net southward flow in the troughs and a net northward flow over the ridges without requiring any transformation of density. In practice both the thermohaline and the eddy/meander mechanisms are likely to be important.

The current flows at a rate of about {{Convert|4|km/h|abbr=on}} over the [[Macquarie Fault Zone|Macquarie Ridge]] south of New Zealand.<ref name="brittlestar">{{cite web |url=http://www.eurekalert.org/pub_releases/2008-05/coml-ema051208.php |title=Explorers marvel at 'Brittlestar City' on seamount in powerful current swirling around Antarctica |access-date=6 June 2008 |date=18 May 2008 }}</ref> The ACC varies with time. Evidence of this is the [[Antarctic Circumpolar Wave]], a periodic oscillation that affects the climate of much of the southern hemisphere.<ref>{{Harvnb|Connolley|2002}}</ref> There is also the [[Antarctic oscillation]], which involves changes in the location and strength of Antarctic winds. Trends in the Antarctic Oscillation have been hypothesized to account for an increase in the transport of the Circumpolar Current over the past two decades.