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Antarctic Zone ((LINK))



The Antarctic (/ænˈtɑːrtɪk/ or /ænˈtɑːrktɪk/, American English also /æntˈɑːrtɪk/ or /æntˈɑːrktɪk/; commonly /æˈnɑːrtɪk/)[Note 1] is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other island territories located on the Antarctic Plate or south of the Antarctic Convergence. The Antarctic region includes the ice shelves, waters, and all the island territories in the Southern Ocean situated south of the Antarctic Convergence, a zone approximately 32 to 48 km (20 to 30 mi) wide varying in latitude seasonally.[4] The region covers some 20 percent of the Southern Hemisphere, of which 5.5 percent (14 million km2) is the surface area of the Antarctica continent itself. All of the land and ice shelves south of 60S latitude are administered under the Antarctic Treaty System. Biogeographically, the Antarctic realm is one of eight biogeographic realms of Earth's land surface.




antarctic zone



As defined by the Antarctic Treaty System, the Antarctic region is everything south of the 60S latitude. The Treaty area covers Antarctica and the archipelagos of the Balleny Islands, Peter I Island, Scott Island, the South Orkney Islands, and the South Shetland Islands.[5] However, this area does not include the Antarctic Convergence, a transition zone where the cold waters of the Southern Ocean collide with the warmer waters of the north, forming a natural border to the region.[6] Because the Convergence changes seasonally, the Convention for the Conservation of Antarctic Marine Living Resources approximates the Convergence line by joining specified points along parallels of latitude and meridians of longitude.[7] The implementation of the convention is managed through an international commission headquartered in Hobart, Australia, by an efficient system of annual fishing quotas, licenses and international inspectors on the fishing vessels, as well as satellite surveillance[citation needed]


The islands situated between 60S latitude parallel to the south and the Antarctic Convergence to the north, and their respective 200-nautical-mile (370 km) exclusive economic zones fall under the national jurisdiction of the countries that possess them: South Georgia and the South Sandwich Islands (United Kingdom), Bouvet Island (Norway), and Heard and McDonald Islands (Australia).


Because Antarctica surrounds the South Pole, it is theoretically located in all time zones. For practical purposes, time zones are usually based on territorial claims or the time zone of a station's owner country or supply base.[24]


Many people have heard that the ozone hole is caused by chemicals called CFCs, short for chlorofluorocarbons. CFCs escape into the atmosphere from refrigeration and propellant devices and processes. In the lower atmosphere, they are so stable that they persist for years, even decades. This long lifetime allows some of the CFCs to eventually reach the stratosphere. In the stratosphere, ultraviolet light breaks the bond holding chlorine atoms (Cl) to the CFC molecule. A free chlorine atom goes on to participate in a series of chemical reactions that both destroy ozone and return the free chlorine atom to the atmosphere unchanged, where it can destroy more and more ozone molecules. For those who know the story of CFCs and ozone, that is the part of the tale that is probably familiar.


These reactions convert the inactive chlorine reservoir chemicals into more active forms, especially chlorine gas (Cl2). When the sunlight returns to the South Pole in October, UV light rapidly breaks the bond between the two chlorine atoms, releasing free chlorine into the stratosphere, where it takes part in reactions that destroy ozone molecules while regenerating the chlorine (known as a catalytic reaction). A catalytic reaction allows a single chlorine atom to destroy thousands of ozone molecules. Bromine is involved in a second catalytic reaction with chlorine that contributes a large fraction of ozone loss. The ozone hole grows throughout the early spring until temperatures warm and the polar vortex weakens, ending the isolation of the air in the polar vortex. As air from the surrounding latitudes mixes into the polar region, the ozone-destroying forms of chlorine disperse. The ozone layer stabilizes until the following spring.


Seven nations have territorial claims in Antarctica: France (Adélie Land), United Kingdom (British Antarctic Territory), New Zealand (Ross Dependency), Norway (Peter I Island and Queen Maud Land), Australia (Australian Antarctic Territory), Chile (Chilean Antarctic Territory), and Argentina (Argentine Antarctica). vThe United States, Peru, Russia, and South Africa have all reserved their right to claim territory in the future. Brazil currently has a "zone of interest" but not an actual claim.


Tintinnid ciliates are important pelagic microplankton. Most studies previously conducted in the Amundsen Sea have covered a relatively small latitude range and provided minimal information about tintinnid species composition and distribution. The present study was conducted to investigate tintinnid assemblages from the Antarctic zone (AZ) northward through the polar front (PF) to the subantarctic zone (SAZ). A total of 17 tintinnid species belonging to seven genera were collected, and 16 were identified. Results show that nine of the species are endemic to the Southern Ocean and they mainly inhabit the AZ near Antarctic continent with an abundant proportion exceeding 60% of total tintinnid. According to the tintinnid abundance distribution, the species were divided into four groups: Group I includes Acanthostomella norvegica, Codonellopsis glacialis, C. pusilla and Cymatocylis antarctica and mainly occurs in the northern boundary of the PF; Group II includes Cymatocylis convallaria forma calyciformis, an unidentified species, and Amphorellopsis quinquealata and mainly inhabits the PF; Group III includes Salpingella costata, Cymatocylis van-hoeffeni, C. convallaria forma cristallina, C. convallaria forma drygalskii, C. convallaria, Codonellopsis gaussi, and Laackman-niella naviculaefera and mainly occurs in the AZ near the Antarctic continent; and Group I V, which comprises Salpingella sp. and inhabits all zones. The new species of tintinnid (belonging to Group II) primarily inhabit the AZ but also are distributed in the PF, and they have large lorica-oral-diameter (LOD). The distribution ranges of tintinnid assemblages from the AZ to PF were determined, in addition to the different assemblages mixed in the PF. The information provided in this study increases our understanding of tintinnid assemblages from the Antarctic continent in the Antarctic Circumpolar Current and Antarctic waters.


Australia, Chile, and Argentina claim Exclusive Economic Zone (EEZ) rights or similar over 200 nm extensions seaward from their continental claims, but like the claims themselves, these zones are not accepted by other countries; 22 of 29 Antarctic Treaty consultative parties have made no claims to Antarctic territory, although Russia and the United States have reserved the right to do so, and no country can make a new claim; also see the Disputes - international entry


the discovery of a large Antarctic ozone hole in the earth's stratosphere (the ozone layer) - first announced in 1985 - spurred the signing of the Montreal Protocol in 1987, an international agreement phasing out the use of ozone-depleting chemicals; the ozone layer prevents most harmful wavelengths of ultra-violet (UV) light from passing through the earth's atmosphere; ozone depletion has been shown to harm a variety of Antarctic marine plants and animals (plankton); in 2016, a gradual trend toward "healing" of the ozone hole was reported; since the 1990s, satellites have shown accelerating ice loss driven by ocean change; although considerable uncertainty remains, scientists are increasing our understanding and ability to model potential impacts of ice loss


Antarctica is administered through annual meetings - known as Antarctic Treaty Consultative Meetings - which include consultative member nations, non-consultative member nations, observer organizations, and expert organizations; decisions from these meetings are carried out by these member nations (with respect to their own nationals and operations) in accordance with their own national laws; more generally, the Antarctic Treaty area, that is to all areas between 60 and 90 degrees south latitude, is subject to a number of relevant legal instruments and procedures adopted by the states party to the Antarctic Treaty; note - US law, including certain criminal offenses by or against US nationals, such as murder, may apply extraterritoriality; some US laws directly apply to Antarctica; for example, the Antarctic Conservation Act, 16 U.S.C. section 2401 et seq., provides civil and criminal penalties for the following activities unless authorized by regulation or statute: the taking of native mammals or birds; the introduction of nonindigenous plants and animals; entry into specially protected areas; the discharge or disposal of pollutants; and the importation into the US of certain items from Antarctica; violation of the Antarctic Conservation Act carries penalties of up to $10,000 in fines and one year in prison; the National Science Foundation and Department of Justice share enforcement responsibilities; Public Law 95-541, the US Antarctic Conservation Act of 1978, as amended in 1996, requires expeditions from the US to Antarctica to notify, in advance, the Office of Oceans and Polar Affairs, Room 2665, Department of State, Washington, DC 20520, which reports such plans to other nations as required by the Antarctic Treaty; for more information, contact antarctica@state.gov


The Antarctic Circumpolar Current (ACC) as represented by theMariano Global Surface Velocity Analysis (MGSVA). The ACC is poorlyrepresented here because of the lack of data. The MGSVA is based onship-drift estimates of sea surface velocities that are mostly availablealong major shipping routes.Click here for example plots ofseasonal averages.The Antarctic Circumpolar Current (ACC) is the most important current inthe Southern Ocean, and the only current that flows completely around theglobe. The ACC, as it encircles the Antarctic continent, flows eastwardthrough the southern portions of the Atlantic, Indian, and Pacific Oceans.Edmond Halley, the British astronomer, discovered theACC while surveying the region during the 1699-1700 HMS Paramore expedition.Later, the famous mariners James Cook in 1772-1775, Thaddeus Bellingshausen(Russia) in 1819-1821, and James Clark Ross in 1839-1843 described theAntarctic Circumpolar Current in their journals.Cook was the firstperson to use the term, Southern Ocean, to describe this area.Other notable expeditions were made by Sir Drake, who reached the tip ofSouth America in 1578, Abel Tasman, who sailed south from Australiainto the Southern Ocean in 1642, James Weddell in 1823, and by theHMS Challenger in 1873-74 (Deacon, 1984).The ACC is arguably the "mightiest current in the oceans" (Pickard and Emery,1990). Despite its relatively slow eastward flow of less than 20 cm s-1in regions between the fronts, the ACC transports more water than any othercurrent (Klinck and Nowlin, 2001).The ACC extends from the sea surface to depths of 2000-4000 m and can beas wide as 2000 km. This tremendous cross-sectional area allows for thecurrent's large volume transport. The Antarctic Circumpolar Current'seastward flow is driven by strong westerly winds. The average wind speedbetween 40S and 60S is 15 to 24 knots with strongest winds typicallybetween 45S and 55S. Historically, the ACChas been referred to as the 'West Wind Drift' because the prevailingwesterly wind and current are both eastward.Without the aid of continental reference point, except for the Drake Passage,where by convention, all flow through the Passage is the ACC, the current'sboundaries are generally defined by zonal variations in specific waterproperties of the Southern Ocean (Gordon et al., 1977). Variations in theseproperties have been used to classify regions whose edges are defined byfronts, where there is rapid changes in water properties which occur overa short distance. North of the ACC is the Subtropical Convergence orSubtropical Front (STF), usually found between 35S and 45S, wherethe average Sea Surface Temperature (SST) changes from about 12C to 7 to 8Cand salinity decreases from greater than 34.9 to 34.6 or less.Three fronts and three zones south of the STF and associated with the ACC are,from north to south;the Subantarctic Zone (SAZ), the Subantarctic Front (SAF), the Polar Frontal Zone (PFZ), the Polar Front (PF), the Antarctic Zone, and the Southern ACC Front. The Antarctic Convergence is approximately 200 kmsouth of the Polar Front. In the Antarctic Convergence, summer SST variesbetween 3C to 5C, while winter SST varies between 1C to 2C.North of the SAF, average Sea Surface Temperature (SST) isgreater than 4C, while south of the Polar front, averageSST is less than 2C.A fourth zone, the Continental Zone, and the westward flowingAntarctic Coastal (or Polar) Currentare located even further poleward, between the Southern Front and the Antarctic continent. SST poleward of 65S is about -1.0C (Deacon, 1984).The eastward flow of the Subantarctic Front (SAF), found between 48S and 58S in the Indian and Pacific Ocean and between 42S and 48S in the Atlantic Ocean, defines the ACC's northern boundary. A region of upwelling, the Antarctic Divergence, occurs at the Southern Front. This area of divergence has been considered to be the ACC's southern boundary (Klinck and Nowlin, 1986)but new analysis puts the southern boundary of the ACC further poleward.Orsi et al. (1995) define the southern boundary of the ACC as thepoleward edge of the Upper Circumpolar Deep Water (T > 1.8C).The southern boundaryof the ACC is approximately at 65S in most of the Indian and Pacific Ocean,from 50E to the dateline; moves northward to 60S, east of the datelineto 140W; is near 70S by 120W and moves northward to 60S, east of the DrakePassage; and northward to 55S at 10E. Northward displacement ofthe southern boundary of the ACC are in the areas of gyres withclockwise surface circulation in the Weddell Sea and in the Ross Sea.Strong, nearly zonal, westerly winds force a large, near-surface,northward Ekman transport and a northward pressure gradient.The ACC current is in approximately geostrophic equilibrium, so thatinclined layers of constant density slope towards the surface poleward acrossthe ACC to balance the current's northward sea surface height elevation.The alignment between the prevailing winds and the resultinggeostrophic current intensifies the ACC. Because stronger gradientsgive rise to stronger flow, the majority of the ACC transport is associatedwith the fronts within the current. Gille (1994) analyzed GEOSAT altimeterdata and found two well-defined jets in the ACC, at the PF and the SAF,with widths between 35 and 50 km and a dominant meander wavelength of 150 km.Other investigators have found meander wavelengths between 100 and 200 km.In the vicinity of the fronts, eastward jets flow at approximately twoto three times the speed of the current found between them(Klinck and Nowlin, 2001). Hoffman (1985) analyzed near-surfacedrifting buoys from FGGE and found average speeds of 20 cm s-1 at the STF, about 40 cm s-1 in the SAF and PF, and from 23 to 35 cm s-1 between fronts. Zambianchiet al. (1999) analyzed eleven WOCE standard drifting buoys, from 1993and 1994,in the Eastern Pacific and found mean speeds greater than 15 cm s-1 north of the PF in the PFZ, and greater than 30 cm s-1 near the PF.They also note strong evidence of topographic steering by thePacific-Antarctic ridge and thatthe floats bifurcate near 150W, 55S with floats either ending up inthe Peru Current via the South Pacific Current or that the floats stayedin the ACC and travelled eastward toward the Drake Passage.Meridional ridges in the bottom topography provide a force balance forthe Atlantic Circumpolar Current by generatingfrictional form drag. As the ACC crosses these ridges, frictional dragdiminishes the current's deep flow (Munk and Palmen, 1951).Bottom topography also controls the path of the ACC, since slowlarge-scale oceanic flows are, on the average, parallel to lines of constantplanetary vorticity (approximately the Coriolis acceleration divided bythe water depth). The Drake Passage, Kerguelen Plateau (and island),Campbell Plateau, Macquarie Ridge, and the Pacific-Antarctic Ridge aremajor topographic features that influence both the mean path of the ACCand its meandering. The degree of topographic blocking will also influence the current's eddy kinetic energy. For example, downstream of meridional ridges there will be an increase in the number of eddies present. Even relatively small eddies make up a significant percentage of the current's overall eddy kinetic energy (Knauss, 1996). Typical time and spacescales of the eddies range from 2 weeks to 2 months and from 50 to 250 km.The path of the ACC is constrained by land where it flows through theDrake Passage, between Cape Horn and the Antarctic Peninsula. To date,the majority of field studies (hydrographic surveys, mooring deployments, etc.)conducted to better understand the ACChave taken place across this 800 km wide passage (Nowlin et al., 1977).Bryden and Pillsbury (1977) found variations over a yearlong currentmeter study across the Drake Passage between 28-290 Sv to a depth of2700 meters. Such a large range of transport values have been foundby numerous oceanographers. Historical transport estimates are listedin Table 1 of Peterson (1988) and Table 6 of Sarukhanyan (1985) andrange from -15 Sv to 262 Sv with several entries greater than 200 Sv.These earlier measurements should be viewed with suspicion since theestimates are aliased by coarse resolution sampling in an energetic eddyfield, and those based on hydrography assume a reference velocity.The most dense set of current meter measurements, during the DRAKE79experiment, yielded a mean transport of 123 Sv and a range of 87 to 148 Sv (Whitworth, 1983; Peterson, 1988). Climatological estimates by Orsi et al (1995) based on hydrographic data show that the ACC transport, relative to 3000 m, is about 100 Sv at all longitudes.Using Drake Passage current meter measurements at 500 meters during theISOS, Wearn and Baker (1980) found the variations with the transportcorrelated with the fluctuations in wind stress when considering periods of longer than 30 days. Similar results are reported for low-frequency time-scales in Peterson (1988) with strong coherence at semi-annual and annualtime scales.In recent years, other areas such as sections of the ACC south of Tasmaniaand New Zealand have also been examined closely. Observations haverevealed a mean ACC transport of 100-150 Sverdrups (1 Sv=106 m3 s-1)that can vary by 50 Sv within time scales as short as a month or two(Knauss, 1996). Variability in the ACC is due to tides (5-10 cm s-1), mesoscale eddies (35-50 cm s-1), near-inertial motion (10 cm s-1), andthose forced by changes in the large-scale wind stress(25 cm s-1) (Sarukhanyan, 1985).The mean ACC temperature ranges from -1 to 5C, depending on the timeof year and location. The mean surface salinity decreases poleward,in general, from 34.9 at 35S to 34.7 at 65S. Typical salinity valuesare between 33.5 and 34.7, poleward of 65S.This Temperature-Salinity signature is due to acombination of water masses that meet in the Souther


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