Traversing the Drake Passage is considered one of the most treacherous voyages for ships to make. TheAntarctic Circumpolar Current, which runs through it, meets no resistance from any landmass, and waves top 40 feet (12 m), giving it a reputation for being "the most powerful convergence of seas".[1]
As the Drake Passage is the narrowest passage (choke point) around Antarctica, its existence and shape strongly influence the circulation of water around the continent andglobal oceanic circulation, and global climate. Thebathymetry of the Drake Passage plays an important part in the global mixing of oceanic water. Part of the water body is namedSouthern Zone Sea.
In 1525, the Spanish navigator,Francisco de Hoces, is assumed to have discovered the Drake Passage after being blown south away from the entrance of theStrait of Magellan.[2] Though he and his ship and crew disappeared, and his exact path and fate are unknown, the Drake Passage is referred to as theMar de Hoces (Sea of Hoces) inSpanish maps and sources, while almost always in the rest of theSpanish-speaking countries it is mostly known asPasaje de Drake (in Argentina, mainly), orPaso Drake (in Chile, mainly).
The passage received its English name fromSir Francis Drake duringhis circumnavigation. After passing in 1578 through the Strait of Magellan withMarigold,Elizabeth, and hisflagshipGolden Hind, Drake entered the Pacific Ocean and was blown far south in a tempest.Marigold was lost andElizabeth abandoned the fleet. Only Drake'sGolden Hind entered the passage.[3] This incident demonstrated to the English that there was open water south of South America.[4]
In 1616, Dutch navigatorWillem Schouten became the first to sail aroundCape Horn and through the Drake Passage.[5]
On December 25, 2019, a crew of six explorers successfully rowed across the passage, becoming the first in history to do so.[6] This accomplishment became the subject of a 2020 documentary,The Impossible Row.[7]
The Drake Passage opened when Antarctica separated from South America due toplate tectonics, however, there is much debate about when this occurred, with estimates ranging from 49 to 17 million years ago.[8][9] TheShackleton fracture zone is under the sea on the Drake Passage zone.
The opening had a major effect on the global oceans due to deep currents, such as theAntarctic Circumpolar Current (ACC). This opening could have been a primary cause of changes in global circulation and climate, as well as the rapid expansion ofAntarctic ice sheets, because, as Antarctica was encircled by ocean currents, it was cut off from receiving heat from warmer regions.[10]
The 800-kilometre-wide (500 mi) passage betweenCape Horn andLivingston 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 toSnow Island (130 kilometres (81 mi) north of mainland Antarctica), though theInternational Hydrographic Organization defines it as the meridian that passes through Cape Horn: 67° 16′ W.[11] Both lines lie within the Drake Passage.
The other two passages around the southern extremity of South America — theStrait of Magellan and theBeagle Channel — have frequentnarrows, leaving little maneuvering room for a ship, as well as unpredictable winds and tidal currents. Most sailing ships thus prefer the Drake Passage, which is open water for hundreds of miles.
No significant land sits at the latitudes of the Drake Passage. This is important to the unimpeded eastward flow of theAntarctic Circumpolar Current, which carries a huge volume of water through the passage and around Antarctica.
The presence of the Drake Passageway allows the three main ocean basins (Atlantic, Pacific and Southern) to be connected via theAntarctic Circumpolar current (ACC), 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. As such, a significant amount of research has been done in understanding how the shape of the Drake passage (bathymetry and width) affects the global climate.
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.[12]
The plot shows a yearly average (2020) of the surface current strength (fromGODAS dataset), together withstreamlines. Following the streamlines, it is easy to see that the current is not closed in itself but interacts with the other ocean basins (connecting them). The Drake Passage plays a major role in this mechanism.
The importance of an open Drake Passage extends farther than theSouthern Ocean latitudes. TheRoaring Forties and the Furious Fifties blow around Antarctica and drive theAntarctic Circumpolar Current (ACC). As a result ofEkman Transport, water gets transported northward from the ACC (on the left-hand side while facing the stream direction). Using aLagrangian approach, water parcels passing through the Drake Passage can be followed in their journey in the oceans. Around 23 Sv of water is transported from the Drake Passage to the equator, mainly in the Atlantic and Pacific Oceans.[13] This value is not far from theGulf Stream transport in theFlorida Strait (33 Sv[14]), but is an order of magnitude lower than the transport of the ACC (100–150 Sv). Water transported from the Southern Ocean to the Northern Hemisphere contributes to the globalmass balance and permits themeridional circulation across the oceans.
Several studies have linked the current shape of the Drake Passage to an effectiveAtlantic meridional overturning circulation (AMOC). Models have been run with different widths and depths of the Drake Passage, and consequent changes in the global oceanic circulation and temperature distribution have been analyzed:[12][15] It appears that the "conveyor belt" of the globalthermohaline circulation appears only in presence of an open Drake Passage, subject towind forcing.[12] With a closed Drake Passage, there is noNorth Atlantic Deep Water (NADW) cell, and no ACC. With a shallower Drake Passage, a weak ACC appears, but still no NADW cell.[15]
It has also been shown that present-day distribution ofdissolved inorganic carbon can be obtained only with an open Drake Passage.[16]
Regarding theglobal surface temperature, an open (and sufficiently deep) Drake Passage cools the Southern Ocean and warms the high latitudes of the Northern Hemisphere. The isolation of Antarctica by the ACC (that can flow only with an open Drake Passage) is credited by many researchers with causing the glaciation of the continent and global cooling in theEocene epoch.
Diapycnal mixing is the process by which different layers of astratified fluid mix. It directly affects vertical gradients, thus it is of great importance to all gradient-driven types of transport and circulation (includingthermohaline circulation). Mixing drives the global thermohaline circulation; without internal mixing, cooler water would never rise 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.[17][18][19] It has been hypothesised that the extra-mixing can be ascribed to breaking ofinternal waves (Lee waves).[20] 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 thediapycnal diffusivity in the Drake Passage is ~20 times the value immediately to the west in the Pacific sector of theAntarctic Circumpolar Current (ACC).[18] Much of the energy that is dissipated through internal wave breaking (around 20% of the wind energy put into the ocean) is dissipated in the Southern Ocean.[21]
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.
Density (buoyancy) drives an internal circulation only if the denser (colder or saltier) water mass lays above the less dense (warmer or less salty) one. In absence of any perturbation, the fluid assumes astratified form. Neglectingsalinity differences, the only possible drivers of such a circulation are vertical temperature differences. However, water gets heated and cooled at the same level, namely at the surface at the equator and at the surface at the poles. The force that pushes colder water above warmer water is internal mixing, which is more intense in presence of rough topography, such as in the Drake Passage.
Historical importance in oceanographic observations
Worldwide satellite measurements of oceanic properties have been available since the 1980s. Before then, data could be only gathered through oceanic ships taking direct measurements. TheAntarctic Circumpolar Current (ACC) has been (and is) surveyed making repeated transects. South America and theAntarctic Peninsula constrain the ACC in the Drake Passage; the convenience of measuring the ACC across the passage lays in the clear boundaries of the current in that stripe. Even after the advent ofsatellite 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 horizontallyand vertically changing quantities (such as velocity inEkman's theory[22]).
^International Hydrographic Organization,Limits of Oceans and Seas, Special Publication No. 28, 3rd edition, 1953[1]Archived 2011-10-08 at theWayback Machine, p.4
