Editing Antarctic Circumpolar Current (section)

== Formation ==
Published estimates of the onset of the Antarctic Circumpolar Current vary, but it is commonly considered to have started at the [[Eocene]]/[[Oligocene]] boundary. The isolation of Antarctica and formation of the ACC occurred with the openings of the [[Tasmanian Passage]] and the [[Drake Passage]], following the fragmentation of the [[Antarctic land bridge]]. The Tasmanian Seaway separates East Antarctica and Australia, and is reported to have opened to water circulation 33.5&nbsp;million years ago (Ma).<ref>{{Harvnb|Hassold|Rea|Pluijm|Parés|2009}}</ref> The timing of the opening of the Drake Passage, between South America and the Antarctic Peninsula, is more disputed. [[Tectonics|Tectonic]] and sediment evidence show that it could have been open as early as pre-34&nbsp;Ma;<ref>{{Harvnb|Barker|Filippelli|Florindo|Martin|2007}}</ref> estimates of the opening of the Drake passage are between 20 and 40&nbsp;Ma.<ref name="Siegert-etal-2008">{{Harvnb|Siegert|Barrett|Deconto|Dunbar|2008}}</ref> The isolation of Antarctica by the current is credited by many researchers with causing the [[glaciation]] of Antarctica and global cooling in the [[Eocene]] epoch. Oceanic models have shown that the opening of these two passages limited polar heat convergence and caused a cooling of [[sea surface temperature]]s by several degrees; other models have shown that CO<sub>2</sub> levels also played a significant role in the glaciation of Antarctica.<ref name="Siegert-etal-2008" /><ref>{{Harvnb|Stott|2011|loc=See "Ancient Current Systems" illustrations at bottom of page}}</ref>