and global cooling in the Eocene epoch. Turbulence and mixing Diapycnal mixing is the process by which different layers of a stratified fluid mix. It directly affects vertical gradients, thus it is of great importance in all the gradient-driven type of transport and circulation (such as the thermohaline circulation). In a simplified way, mixing drives the global thermohaline circulation: without internal mixing, cooler water would never be above warmer water, and there would be no density(buoyancy)-driven circulation. However, mixing in the interior of most of the ocean is thought to be ten times weaker than required to support the global circulation. It has been hypothesised that the extra-mixing can be ascribed to breaking of internal waves (Lee waves). When a stratified fluid reaches an internal obstacle, a wave is created that can eventually break, mixing the fluid’s layers. It has been estimated that the diapycnal diffusivity in the Drake Passage is ~20 times the value immediately to the west in the Pacific sector of the Antarctic Circumpolar Current. Much of the energy that is dissipated through internal wave breaking (around 20% of the wind energy put into the ocean) gets dissipated in the southern ocean. In short, without the coarse topography in the depths of the Drake Passage, oceanic internal mixing would be weaker, and the global circulation would be affected. Historical importance in oceanographic observations Worldwide satellite measurements of oceanic properties are available since the 1980s. Before then, data could be only gathered through oceanic ships taking direct measurements. The Antarctic Circumpolar Current has been (and is) surveyed making repeated transects. South America and the Antarctic Peninsula constrain the Antarctic Circumpolar Current in the Drake Passage: the convenience of measuring the Antarctic Circumpolar Current across the passage lays in the clear boundaries of the current in that stripe. Even after the advent of satellite altimetry data, direct observations in the Drake Passage have not lost their exceptionality. The relative shallowness and narrowness of the passage makes it particularly suitable to assess the validity of horizontally and vertically changing quantities (such as velocity in Ekman’s classic theory). In addition, the strength of the Antarctic Circumpolar Current makes meanders and pinching cold-core cyclonic rings easier to observe. Fauna Wildlife in the Drake Passage includes the following species: Birds Cetaceans Gallery See also Elizabeth Island (Cape Horn) Garcia de Nodal expedition Bransfield Strait Sars Bank Timeline of Francis Drake's circumnavigation References External