Antarctic ice sheets, because as Antarctica was encircled by ocean currents it was cut off from receiving heat from warmer regions. Precise dating of the earliest opening of the Drake Passage is complicated by the existence of plate fragments, which have been reconstructed to show the age of the earliest opening. The passage between Cape Horn and Livingston Island is the shortest crossing from Antarctica to another landmass. The boundary between the Atlantic and Pacific Oceans is sometimes taken to be a line drawn from Cape Horn to Snow Island ( north of mainland Antarctica), though the International Hydrographic Organization defines it as the meridian that passes through Cape Horn—67° 16′ W. Both lines lie within the Drake Passage. The other two passages around the extreme southern part of South America (though not going around Cape Horn as such), the Strait of Magellan and Beagle Channel, are narrow, leaving little maneuvering room for a ship. They can become icebound. Sometimes the wind blows so strongly that no sailing vessel can make headway against it. Most sailing ships thus prefer the Drake Passage, which is open water for hundreds of miles. The small Diego Ramírez Islands lie about south-southwest of Cape Horn. No significant land sits at the latitudes of the Drake Passage. That is important to the unimpeded flow eastward of the Antarctic Circumpolar Current, which carries a huge volume of water through the passage and around Antarctica. The passage hosts whales, dolphins and seabirds including giant petrels, other petrels, albatrosses and penguins. Importance in physical oceanography The presence of the Drake Passage allows the three main ocean basins (Atlantic, Pacific and Indian) to be connected via the Antarctic Circumpolar current, the strongest oceanic current, with an estimated transport of 100–150 Sv (Sverdrups, million m3/s). This flow is the only large-scale exchange occurring between the global oceans, and the Drake passage is the narrowest passage on its flow around Antarctica. A significant amount of research has been done in understanding how the shape of the Drake passage (bathymetry and width) affects the global climate. Oceanic and climate interactions "Major features of the modern ocean’s temperature and salinity fields, including the overall thermal asymmetry between the hemispheres, the relative saltiness of deep water formed in the northern hemisphere, and the existence of a transequatorial conveyor circulation, develop after Drake Passage is opened". The importance of an open Drake Passage extends far