Who decides where the Atlantic Ocean ends and the Pacific begins? The International Hydrographic Organization, that's who. Founded in 1921, the Monaco-based group issues a publication titled "Limits of Oceans and Seas" that sets out ocean boundaries. The borders, more significant to researchers than to sailors, have no political significance whatsoever. No oil-drilling rights or territory is at stake. So where do the Atlantic and Pacific meet? The agreed-upon line extends directly south from Cape Horn to Antarctica. In 2000, the IHO's 70-plus members also set the limits for a newly designated body of water: The Southern Ocean comprises the waters surrounding Antarctica, out to 60 degrees south latitude.
Source: 'Do Elephants Jump?' by David Feldman (HarperCollins 2004), www.wikipedia.org, www.iho.shom.fr