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Southern Thule
Southern Thule
Southern Thule
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Southern Thule is a group of the three southernmost islands in the South Sandwich Islands in the southern Atlantic Ocean: Bellingshausen, Cook, and Thule (Morrell). It is a largely submerged volcano of which only the three islands emerge above sea level. Between Cook and Thule, and south of Bellingshausen, lie two submerged calderas; a third caldera is located on Thule. Cook Island is inactive and largely glaciated, while Bellingshausen and Thule feature active craters with fumarolic activity, and evidence of eruptions in the 20th century.

Key Information

Around the fumaroles, vegetation consisting of mosses and lichens has grown. The islands are populated by penguins and seabirds which breed there. The islands were discovered in 1775 and are uninhabited. They are part of a marine protected area that is part of the British Overseas Territory of South Georgia and the South Sandwich Islands.

Geography and geology

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Regional

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Southern Thule is the southernmost island group in the South Sandwich Islands,[2] an archipelago in the Southern Atlantic Ocean.[3] The South Sandwich Islands are a group of eleven volcanic islands, most of which are volcanically active.[4] They are located about 2,000 kilometres (1,200 mi) north of Antarctica and about the same distance southeast from the Falklands Islands.[1] Politically, the South Sandwich Islands are a UK overseas territory and managed as part of the South Georgia and South Sandwich Islands. They were declared a marine protected area in 2012, with additional expansion taking place in 2019.[5]

Local

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The Southern Thule group consists of three islands, the southern-most pair Thule Island and Cook Island, and the smaller Bellingshausen Island to their northeast.[6] They rise from an east-west trending[7] wave-cut platform on top of a broad submerged volcano with a width of 30 kilometres (19 mi),[8] and a length of 63 kilometres (39 mi) at 2,000 metres (6,600 ft) depth. The western side of the volcano has steeper slopes than the eastern side.[9] The flanks of this volcano feature ridges and domes, as well as traces of mass wasting such as chutes.[10] The islands are surrounded by shallow shelves at 120–130 metres (390–430 ft) depth, which probably formed through erosion during glacial periods, when sea levels were lower.[11] Several seamounts lie south and west of Southern Thule, including Kemp Caldera, Adventure Bank and Nelson Seamount.[12]

Bellingshausen and Thule Islands are both simple volcanic cones with a summit crater. The crater on Thule is water-filled, and there is a parasitic vent on the southeastern side of the island. Cook Island is more complex and might consist of multiple volcanic cones.[13] Where there are outcrops, all three islands appear to consist of layers of lava flows and scoria or pyroclastics.[14]

  • Bellingshausen Island has dimensions of 1.2 by 1.7 kilometres (0.7 mi × 1 mi), with a north-south orientation.[15] It is roughly triangular with Salamander Point in the north, Hardy Point in the southwest, and Isaacson Point in the southeast. A further pedunculate peninsula juts out from the northeastern side and forms Jagged Point.[16] The coasts are dominated by cliffs, lava shelves and beaches. Inland, slopes and terraces emanate from the summit crater.[17] The highest point of the island is Basilisk Peak; its elevation above sea level is variously given as 182 metres (597 ft)[14] or 253 metres (830 ft). The about 500-metre (1,600 ft) wide[8] summit crater is about 60-metre (200 ft) deep and drained underground.[17] In the cliffs and the crater there are outcrops of lava flows and scoria.[18] Unlike the other two islands, Bellingshausen is almost free of ice,[8] with most of the terrain covered with scoria[19] or lava flows.[20] The ice features crevasses.[17]
  • Cook Island has dimensions of 6 by 3.5 kilometres (3.7 mi × 2.2 mi) and is rectangular in shape, extending east-west.[21] The "corners" are formed by the northwestern cape at Tilbrook Point, the northeastern cape at Resolution Point, the southeastern cape at Longton Point and the southwestern cape at Reef Point. There is also an eastern cape at Swell Point and southern one at Jeffries Point.[22] The island is almost entirely surrounded by cliffs,[21] except at narrow locations and where glaciers enter the sea.[22] Mount Holdgate and 1,075-metre (3,527 ft) high Mount Harmer rise on the eastern side of the island,[23] which features several cone-shaped peaks.[24]
  • Thule Island has dimensions of 5.2 by 5.4 kilometres (3.2 mi × 3.4 mi) and has a trapezoid shape with the broad side towards the east. The capes of the trapezoid are formed by Cape Flannery to the southwest, Morrell Point to the northwest and Beach Point to the northeast, while the southeastern end has a complex shape: Hewison Point projects far from the coast towards Twitcher Rock, while Herd Point farther south delimits a bay between Hewison Point and Herd Point, Ferguson Bay.[25] The coasts are formed by alternations of ice cliffs, regular cliffs, rocky platforms and rocky shelves,[26] with bouldery beaches providing access to the island.[27] The highest point is 725 metres (2,379 ft) high Mount Larsen.[25] The inland of Thule features a large, 1.7-kilometre (1.1 mi) wide caldera[28] with hints of a 500–600-metre (1,600–2,000 ft) wide inner crater.[29] One observation in 1962 found a 60-metre (200 ft) deep volcanic crater with a green crater lake,[26] which in another survey in 1997 had been replaced by a depression in the ice cover.[30] The two western capes may have been formed by lava flows that exited the caldera on its western side.[29]

Between Cook and Thule Island lies the Douglas Strait with a 4.8 by 4.3 kilometres (3.0 mi × 2.7 mi) caldera[31] at 620 metres (2,030 ft) depth.[32] Elsewhere, the sea between the two islands only reaches depths of 55 metres (180 ft)[33] and the strait is no more than 6-kilometre (3.7 mi) wide,[34] its seafloor covered with sediment.[35] The caldera floor contains a debris mound that may have formed from a landslide at Thule Island.[31] Other features are concentric arches that may indicate that the caldera is nested, and large cones that could be tephra cones.[36] Another submarine caldera is located south of Bellingshausen Island and east of Cook Island;[34] it is named Resolution Caldera and is open to the south.[7] It reaches a depth of 276 metres (906 ft) below sea level, while its eastern rim rises to a depth of 35 metres (115 ft), and has a width of 3–4 kilometres (1.9–2.5 mi).[9] The Douglas Strait caldera has an estimated volume of 9–12 cubic kilometres (2.2–2.9 cu mi) and the Resolution one of 3 cubic kilometres (0.72 cu mi); both may have formed through multiple eruptions.[37]

Composition

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Bellingshausen has produced basaltic andesite, while Cook volcanic rocks range from basalt to dacite[13] and Thule has produced andesite and dacite. Phenocrysts include augite, hypersthene and plagioclase.[38] All volcanic rocks define a predominantly tholeiitic suite,[39] but there are calc-alkaline members.[40] The tholeiitic magmas form through the melting of pyrolite mantle triggered by the entry of water released from the subducted crust in about 80–100 kilometres (50–62 mi) depth. The calc-alkaline magmas form when the subducted crust undergoes a transformation into eclogite-quartz at depths of 100–300 kilometres (62–186 mi), which upon melting yields the calc-alkaline melts.[41] Palagonite tuffs crop out on Bellingshausen[42] and Thule.[38]

Climate, vegetation and animal life

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Mean temperatures in the South Sandwich Islands hover around freezing;[43] at Southern Thule they are estimated to range between −1 and −11 °C (30 and 12 °F).[44] Sea ice covers the sea for about three months a year,[30] and wave heights reach 15 metres (49 ft).[12] Winds blow mostly from south and northwest, and frequent extratropical cyclones and storms pass through the archipelago. The sky is usually overcast, with frequent precipitation falling mostly as snow.[45]

Bellingshausen Island is richly vegetated, with mosses and hepatics growing all around the fumaroles and even away from them. They are in turn colonized by collemboles and mites.[21] The plant communities around the fumarolic vents form characteristic concentric populations,[19] while mosses form carpets in gullies.[46] Cook Island by contrast appears to be lacking vegetation entirely, even if lichens may be present,[47] and Thule Island likewise seems to largely lack vegetation[48] except for lichens.[49] The flora resembles that of Antarctic and South Atlantic cold temperate climate zones.[50]

Chinstrap penguins and macaroni penguins nest on Bellingshausen and Thule Island, as well as gulls, skuas, snow petrels and Wilson's petrels.[51] Fur seals and southern elephant seals breed on the islands.[52] Antarctic petrels,[53] Antarctic terns,[54] emperor penguins and king penguins also visit the islands.[55]

The principal animals on the submarine slopes of Southern Thule are annelids, crustaceans, molluscs and nematodes.[56] The shallow waters around Southern Thule provide habitats for sea spiders.[57] The submarine habitat may have been severely impacted by the formation of the Douglas Strait caldera and the eruption that caused it.[58] Presently, frequent mass wasting regularly buries the submarine slopes, devastating faunal communities.[59]

Eruption history

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The simple structure of Bellingshausen Island implies it is probably among the most recently formed of the South Sandwich Islands.[60] Thule and Cook Islands probably were once part of a common volcano centered on Douglas Strait, but large parts of both islands formed independently from this common volcano.[48] Some landforms in the caldera are very fresh and may have formed recently.[24] The Douglas Strait caldera may have formed only a few thousands of years ago.[58]

Fumaroles have been observed in the summit craters of Bellingshausen and Thule, while Cook displays no evidence of fumarolic activity.[13] The Bellingshausen fumaroles occur around the southern side of the crater and their vents have various shapes and sizes. Some are surrounded by sulfur deposits. Parts of the island are heated from below.[60] The composition of fumarolic gases at Bellingshausen shows a predominance of water vapor, with lesser quantities of carbon dioxide and traces of hydrogen and hydrogen sulfide.[61]

In 1963, volcanic ash was observed overlying ice on the southwestern side of Thule, perhaps indicating a recent eruption.[13] A similar observation was made with scoria on Thule Island the preceding year, when a secondary crater may have been active.[48] Several craters formed on the southern flank of Bellingshausen Island between 1964 and 1997.[32] Seismic activity has been recorded around Southern Thule.[62] There are no known eruptions at Cook Island[47] nor any recorded hydrothermal activity in Douglas Strait[31] or Resolution caldera.[63]

Human history

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Penguins and human structures at Hewison Point

The South Sandwich Islands were discovered by James Cook in 1775.[2] He also saw the peaks of the Southern Thule group, and named them "Thule" as they were the southernmost land known at that time.[64] The Bellingshausen expedition of 1819 established that "Southern Thule" was a group of three islands, naming one of them Cook Island after their discoverer. Later, the islands were visited by sealers, which may have overexploited the seals of the archipelago, leading to their almost-disappearance.[65] The hostile conditions and remote location mean that they are seldom visited.[34]

Occupation

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In 1954–1956, Argentina built a hut on Thule Island, at Hewison Point, and named it "Teniente Esquivel". It was abandoned following a large eruption on nearby Bristol Island.[66] At the same place, Argentina built a military outpost "Corbeta Uruguay".[67] and maintained it from 1976 to 1982. Britain discovered the Argentine presence in 1976. The Argentine occupants were removed and the base was destroyed in 1982 as part of Operation Keyhole.

References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Southern Thule

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Southern Thule is a remote, uninhabited group of three small volcanic islands—Thule, Cook, and Bristol—forming the southernmost segment of the South Sandwich Islands in the Scotia Sea of the South Atlantic Ocean. These islands, part of the British Overseas Territory of South Georgia and the South Sandwich Islands, emerged above sea level within the last few thousand years as overlapping volcanic edifices in the South Sandwich island arc, driven by subduction of the South American Plate beneath the Scotia Plate. The barren terrain, covered in glaciers and subject to frequent volcanic activity and extreme Antarctic weather, supports minimal vegetation and no permanent human habitation, rendering the group among the most isolated landmasses on Earth. Historically, the islands saw brief human intervention when Argentina established a meteorological station on Thule Island in 1976, which British forces dismantled in 1982 following the Falklands War. Today, Southern Thule lies within a marine protected area, valued for its geological and ecological significance despite limited scientific access due to its inaccessibility.

Geography

Regional context and location

Southern Thule forms the southernmost cluster of islands in the , a remote chain of eleven volcanic islands situated in the of the . The extends approximately from 56°S to 60°S and lies 350 to 500 miles southeast of . As part of the British Overseas Territory of South Georgia and the , the region is characterized by its extreme isolation, with no permanent human habitation and limited accessibility due to harsh weather and distance from major landmasses. The Southern Thule group consists of three principal islands—, Cook, and Bellingshausen—aligned in an east-west orientation along the southern terminus of the South Sandwich island arc, which borders the to the north. Centered at roughly 59.45°S and 27.37°W , these islands emerge from the subduction zone dynamics of the South American Plate subducting beneath the South Sandwich Trench, contributing to the volcanic nature of the entire chain. The surrounding maritime zone encompasses over 1,000,000 km², designated as a emphasizing the pristine oceanic environment.

Constituent islands and physical features

Southern Thule consists of three islands—Bellingshausen, Cook, and —emerging from a largely submerged volcanic edifice at the southern terminus of the South Sandwich island arc. These islands align east-west along the arc, with their summits representing the subaerial portions of constructs rising from oceanic depths exceeding 3,000 meters. The group spans approximately 10 kilometers in an east-west direction, characterized by rugged, glaciated terrain dominated by volcanic cones, calderas, and ice caps influenced by ongoing . Bellingshausen Island, the easternmost, exhibits a youthful stratocone profile with a maximum elevation of 253 meters. It features a symmetrical snow-clad form, an extensive lava field on its southern flank, and a small summit explosion crater active between 1964 and 1986. The island's morphology includes steep slopes and limited dissection, reflecting relatively recent construction. Cook Island, the central and largest island, reaches 1,075 meters in elevation and is flanked by a submarine measuring 4.3 by 4.8 kilometers, which forms Douglas Strait separating it from . Its terrain is heavily dissected along the coasts with multiple steep-sided, snow-covered cones indicative of spatter eruptions, suggesting it as the oldest of the trio. Thule Island, to the west, attains 572 meters elevation and possesses a triangular outline with an ice-filled summit 1.5 to 2 kilometers wide. The island displays pronounced coastal dissection and evidence of flank collapse, contributing to sediment deposits in adjacent submarine features. Volcanic heat maintains ice-free conditions within parts of its .

Geology

Tectonic setting

Southern Thule forms the southernmost segment of the , an intra-oceanic convergent margin where the South American Plate subducts westward beneath the overriding Sandwich Plate at a rate of 70–80 mm per year. This subduction initiates at the South Sandwich Trench, approximately 200–300 km east of the islands, with the descending slab exhibiting a Benioff zone that dips at angles of 40–60° beneath the arc. The process generates partial melting in the overlying mantle wedge due to fluxing by volatiles from the subducting slab, producing primarily calc-alkaline magmas that ascend to form the arc's stratovolcanoes. The islands of Southern Thule—Bellingshausen, Cook, and (also known as Morrell)—emerge as the subaerial summits of a single, elongate volcanic edifice aligned east-west parallel to the , spanning roughly 20 km in length and situated about 100 km arcward from the front. Oblique convergence along this margin, influenced by the regional tectonics of the Scotia Plate, contributes to back-arc extension in the adjacent East Scotia Ridge, though the primary volcanic construction at Southern Thule remains tied to frontal arc processes rather than extension. Seismic activity reflects the seismogenic nature of the subduction zone, with intermediate-depth earthquakes tracing the slab's descent, but the potential for great (magnitude >8) earthquakes remains uncertain due to the young age and limited historical data of the system.

Volcanic composition and structure

Southern Thule forms a complex volcanic edifice at the southern terminus of the South Sandwich arc, characterized by three stratovolcanoes aligned along an east-west trend: (westernmost, summit elevation 572 m), Cook Island (central, summit elevation 1,075 m), and Bellingshausen Island (easternmost, summit elevation 253 m). These edifices emerge from the subduction zone where the South American Plate descends beneath the Sandwich Plate, resulting in intra-oceanic arc volcanism with thin less than 15 km thick. The group features multiple structures, including an ice-filled summit on (1.5–2 km wide), a submarine in Douglas Strait between Cook and Thule Islands (4.3 × 4.8 km), and evidence of post- volcanism such as pyroclastic cones or pillow mounds within Thule's nested system, marked by arcuate fault scarps suggesting recent collapse possibly within the last few centuries. A potential additional submarine lies east of Cook Island and south of Bellingshausen, contributing to the edifice's structural complexity. Bellingshausen Island exhibits a youthful morphology with an extensive on its southern flank and a small active between 1964 and 1986, indicative of effusive and minor explosive activity building its low-relief profile. Cook Island, in contrast, represents a more mature stage of arc evolution, with its submarine in Douglas displaying geomorphologically fresh features consistent with relatively young formation and potential hydrothermal influence, though direct evidence from temperature or salinity anomalies remains absent. Thule Island's hosts a large mound (~1,000 m³) linked to flank , underscoring ongoing instability in the system's structure. The volcanic rocks of Southern Thule span a compositional range from to silicic, including picro-basalt, , , , and , reflecting differentiation processes within the subduction-related magmatic system. This variability aligns with the South Sandwich arc's overall tholeiitic to calc-alkaline spectrum, where Southern Thule's lavas show calc-alkaline affinities, particularly on Cook and Thule Islands, driven by hydrous flux melting of the mantle wedge. Eruptive products include porphyritic and dominant in the arc, with silicic differentiates indicating processes such as and crustal assimilation, though sampling limitations highlight potential underrepresentation of diversity on smaller islands like Bellingshausen.

Climate and ecology

Climatic characteristics

The climate of Southern Thule is classified as polar maritime, marked by consistently low temperatures, high wind speeds, and substantial precipitation influenced by its position within the and proximity to Antarctic waters. This oceanic influence results in frequent cyclonic storms and rapid weather shifts, with the islands' volcanic topography exacerbating local orographic effects on wind and moisture. Direct meteorological observations are limited due to the absence of permanent stations, relying instead on expedition records, satellite data, and regional models from the South Sandwich archipelago. Temperatures remain near or below freezing year-round, with average winter lows reaching -6°C and minimal seasonal variation due to maritime moderation. Recorded extremes at South Thule include minima of -29.8°C during cold outbreaks and maxima around 18°C in rare summer thaws, though sustained highs rarely exceed 5°C. Annual means approximate 0°C to -2°C, with summer (December-February) averages slightly above freezing and winter (June-August) values dropping to -5°C or lower, reflecting the harsh sub-Antarctic conditions colder than those at northern South Sandwich sites. Precipitation is abundant and persistent, often exceeding 2000 mm annually in equivalent form, predominantly as , sleet, or fine , contributing to snow cover on higher elevations despite volcanic heat sources. Wind regimes are dominated by amplified by the low-pressure systems of the , with frequent gales exceeding 100 km/h and mean speeds of 20-30 km/h, posing significant hazards to and terrestrial stability. These conditions underscore the islands' isolation and extremity, with and low visibility common year-round.

Vegetation, wildlife, and biodiversity

The vegetation of Southern Thule is characteristically sparse and low-growing, dominated by non-vascular plants adapted to the islands' cold, windy, volcanic soils and frequent ash deposition. (mosses and liverworts) and lichens form the primary cover, with 38 species and 11 liverwort species recorded across the , many of which exhibit affinities to South American (32% of mosses) or bipolar/cosmopolitan distributions (45% of mosses). from fumaroles and volcanic activity enables localized, more luxuriant communities on unheated or warmed ground, including species like Campylopus introflexus, contrasting with the maritime Antarctic-like on cooler terrains; however, no native vascular plants (phanerogams) are established on Southern Thule itself, reflecting the group's extreme southern and instability. Wildlife centers on marine and avian species, as the islands lack mammals or reptiles. Seabirds breed in large colonies, with chinstrap penguins (Pygoscelis antarctica) predominant, contributing to an archipelago-wide estimate of approximately 1.5 million breeding pairs (about 30% of the global population). Other key breeders include Antarctic fulmars (Fulmarus glacialoides), petrels (Daption capense), and petrels (Pagodroma nivea), alongside rarer records of black-bellied storm petrels (Fregetta tropica) and Antarctic terns (Sterna vittata). fur seals (Arctocephalus gazella) are the only confirmed breeding , with small pup counts and expanding sites noted in surveys; occasional sightings of southern elephant seals (Mirounga leonina) and other species occur but lack verified breeding. Terrestrial are depauperate, comprising 29 free-living micro-arthropod (9 Collembola springtails and 20 Acari mites) across the South Sandwich Islands, with no macro- like beyond occasional transients. Overall on Southern Thule remains low due to isolation, , and climatic severity, but the islands hold global significance for avian reproduction, supporting substantial fractions of key populations while surrounding waters host richer benthic and pelagic communities, including vulnerable marine ecosystems.

Volcanic activity

Eruption history

Southern Thule's documented eruptive activity is limited, primarily involving explosions and minor effusive events on Thule and Bellingshausen islands, with Cook Island showing no historical eruptions. In March 1962, a approximately 150 m wide opened on the thickly glaciated southwestern flank of , accompanied by scoriaceous material observed on the ice above the south coast and ash deposits on the ice surface near the summit . Between 1964 and 1986, a small formed on the southern flank of Bellingshausen Island, associated with ash deposits on ice and a youthful in the vicinity. The most recent confirmed eruption occurred on July 2, 1975 (±11 years uncertainty), involving activity and parasitic formation on the south flank of Bellingshausen Island, with an estimated (VEI) of 1 and both explosive and effusive components. Ongoing fumarolic activity persists at craters on Thule and Bellingshausen islands, maintaining ice-free zones amid the glaciated terrain, while seismic monitoring has detected intermittent activity around the island group. No eruptions have been confirmed since , though the subduction-related tectonic setting suggests potential for future activity.

Recent and potential hazards

The most recent confirmed eruption of Southern Thule occurred around on the south flank of Bellingshausen Island, involving explosions and effusive activity that formed a parasitic , with a (VEI) of 1. Earlier 20th-century signs of unrest included steam emissions observed at the summit of Thule Island in 1962 and ash deposits on ice surfaces at Thule and Bellingshausen Islands. No eruptive activity has been reported since , and routine satellite monitoring, such as via MIROVA detection systems, has detected no anomalies as of 2025. Potential hazards stem primarily from the volcano's youthful morphology, ice-covered flanks, and proximity to submarine features like calderas in Dawson Strait and Resolution Trough, which record past explosive events. Future eruptions could involve explosive phreatomagmatic interactions between ascending and glacier ice or seawater, generating plumes, pyroclastic flows, and rapid ice melt leading to localized floods or steam explosions. Such events have disrupted ecosystems across the South Sandwich arc, with and smothering vegetation, contaminating freshwater sources, and altering marine habitats through acidification and sediment loading. Gas emissions, including , pose ongoing risks to aerial and marine wildlife by inducing respiratory stress and chemistry changes. Submarine volcanism around Southern Thule increases tsunami potential from caldera collapses or landslides, though the remote location minimizes direct human threats, with zero population within 100 km. Ecological vulnerabilities are heightened for endemic species, such as seabird colonies and benthic communities, where recurrent activity could exacerbate habitat loss in this polar setting. Limited accessibility constrains ground-based hazard assessment, relying on remote sensing for early warnings during expeditions or fisheries operations.

Human exploration and presence

Discovery and early expeditions

The Southern Thule island group, comprising Cook Island, Thule Island, and Bellingshausen Island, was first sighted on January 31, 1775, by Captain James Cook during his second circumnavigation of the globe aboard HMS Resolution. Cook observed the distant peaks emerging from heavy fog and snowstorms, naming the formation "Southern Thule" to denote its position as the southernmost extent of his discoveries, evoking the mythical northern Thule of ancient geography. Adverse weather conditions, including gale-force winds and poor visibility, prevented any landing or detailed survey, though Cook charted its approximate latitude at 59°30'S and claimed the South Sandwich Islands, including this group, for Britain. Further exploration occurred in 1820 during the Russian Antarctic Expedition led by aboard the sloops Vostok and Mirny. Approaching closer than Cook had, Bellingshausen resolved the apparent single landmass into three distinct islands, confirming their volcanic nature through observations of steam vents and ash deposits. He named the central island , the largest eastern island Cook Island in honor of the earlier explorer, and the western island Bellingshausen Island after himself; no landings were attempted due to treacherous seas and ice, but the expedition's surveys provided the first reliable mapping of the group's configuration at roughly 59°27'S, 27°17'W. Subsequent early 19th-century passages by sealing vessels occasionally sighted the islands en route to fur-sealing grounds, but the remoteness, frequent volcanic activity, and lack of sheltered anchorages deterred systematic expeditions or human presence until the late 1800s. These initial sightings established Southern Thule's reputation as one of the most isolated and inhospitable archipelagos in the , with exploration limited to visual reconnaissance from passing ships.

Modern settlement attempts and evacuation

In November 1976, Argentine forces established the Corbeta Uruguay outpost on , the principal component of Southern Thule, without notifying the , which administers the as a British Overseas Territory. The installation, comprising prefabricated structures for meteorological observations and staffed by approximately 11 personnel including and civilian elements, aimed to assert Argentine sovereignty claims in the region. Upon detecting the presence via in December 1976, Britain issued diplomatic protests asserting its territorial rights but refrained from countermeasures at the time. The outpost persisted until the , during which Argentina briefly reinforced it amid broader hostilities. British forces executed on 19–20 June 1982, deploying rifle troops from via HMS Yarmouth, RFA Olmeda, and the tug Salvageman. The garrison of ten Argentines—nine naval personnel and one civilian—surrendered unconditionally without combat, marking the final Argentine-held position in the conflict. The personnel were detained and transported aboard RFA Olmeda for repatriation, while the base facilities were dismantled or destroyed to prevent reuse. No subsequent permanent human settlements have been established on Southern Thule, consistent with the uninhabited status of the , though transient visits for scientific monitoring, such as automated maintenance, continue sporadically.

Territorial administration and claims

The , including the Southern Thule archipelago (comprising Thule Island, Cook Island, and Morrell Island), form part of the British Overseas Territory of South Georgia and the South Sandwich Islands (SGSSI), under continuous administration by the since their annexation via in 1908. Governance is exercised by a Commissioner for SGSSI, appointed by the British monarch and typically holding concurrent roles such as ; the current Commissioner is Colin Martin-Reynolds, effective from 29 July 2025. The UK maintains no permanent civilian population or infrastructure on Southern Thule, with administration focused on conservation, scientific research, and occasional military patrols from bases in the . asserts over the , designating them as part of its claimed sector within the broader Malvinas/Falklands dispute, with formal claims dating to a 1938 decree though initial protests against British title emerged only in 1927 for and later for the Sandwiches. This position was actively demonstrated in November 1976 when Argentine forces covertly established the Corbeta Uruguay military base on , housing approximately 50 personnel under the guise of a meteorological station; the outpost was dismantled and personnel evacuated by British naval forces on 20 1982 during , amid the . continues to reject British , reaffirming its claims in diplomatic statements as recently as 2022, but the upholds exclusive title without international recognition of Argentine pretensions beyond supportive votes in UN decolonization committees. No other states maintain active territorial claims to the area.

Chagossian relocation and associated controversies

The , an ethnic group originating from the in the , were forcibly removed from their homes between 1968 and 1973 by the at the behest of the to facilitate the construction of a on , affecting approximately 1,500 to 2,000 individuals who were relocated primarily to and the . This relocation has sparked ongoing legal and controversies, including court rulings declaring the expulsions unlawful and international calls for reparations and the , though resettlement remains restricted on due to its strategic military role. Southern Thule, comprising the southernmost islands of the in the , has no historical or documented connection to the Chagossian relocation. The , including Southern Thule, have never supported permanent human settlements due to their extreme Antarctic climate, frequent volcanic eruptions, and logistical inaccessibility, with human presence limited to brief 19th-century operations and modern scientific expeditions. No records indicate any proposal, attempt, or controversy involving Chagossian resettlement or displacement in relation to these islands, which fall under the separate administration of the British Overseas Territory of and the . The geopolitical sensitivities surrounding Chagossian rights pertain exclusively to the and do not extend to the uninhabited, sub-Antarctic environment of Southern Thule.

Significance and conservation

Ecological and scientific value

Southern Thule's remote and extreme environment, dominated by volcanic activity and conditions, supports limited terrestrial consisting primarily of sparse, cold-adapted lichens, mosses, and grasses, with no forests or higher plants due to the harsh climate and frequent ashfalls. The islands host significant populations, including mixed breeding colonies of Adélie penguins (Pygoscelis adeliae) and chinstrap penguins (Pygoscelis antarcticus) on , contributing to the region's role as a and breeding ground for avifauna. Marine mammals are represented by Antarctic fur seals (Arctocephalus gazella), which maintain breeding colonies, alongside occasional sightings of southern elephant seals (Mirounga leonina) and other pinnipeds during surveys. Submarine and benthic ecosystems around Southern Thule exhibit suppressed compared to northern , with high dominance by a few resilient species adapted to steep bathymetric gradients and variable cover. Deep-sea communities include diverse cephalopods, crustaceans, and , with 12 species newly recorded for the in recent dietary analyses of predators, highlighting connectivity to and faunas. Bacterioplankton assemblages in surface waters form a of broader marine microbial communities, influenced by local oceanographic dynamics. Scientifically, Southern Thule's active , featuring an ice-filled on and submarine calderas nearby, serves as a key site for studying subduction-related and island-building processes in the . Observations of exposed lavas, pyroclastic deposits, and hydrological features on Cook Island provide insights into eruptive history and freshwater systems in volcanic settings. The area's isolation enables long-term monitoring of pristine ecosystems, including ocean currents, variability, and predator-prey interactions, supporting research on climate impacts and marine connectivity in the region. Recent expeditions have emphasized its potential as a global reference for baseline and studies amid minimal human disturbance.

Protected status and management

The entire landmass of the South Sandwich Islands, including Southern Thule, was designated as a Specially Protected Area under the Wildlife and Protected Areas (Specially Protected Areas) Order 2022, effective July 5, 2022, encompassing over 3,800 km² of terrestrial habitat. This designation prohibits all human entry without a permit from the Government of South Georgia and the South Sandwich Islands (GSGSSI), aiming to prevent introductions of invasive species and maintain the archipelago's near-pristine ecosystem, which supports significant seabird populations such as Adélie penguins on Southern Thule. Surrounding waters form part of the and (SGSSI ), established on February 23, 2012, and expanded on June 13, 2013, to cover 1.24 million km² under IUCN Category VI for sustainable use. Within this, a 3-nautical-mile no-take zone encircles each , totaling 2,272 km² and barring all extractive activities to safeguard benthic habitats and foraging grounds for predators. is prohibited across the entire to protect vulnerable ecosystems, while licensed for species like is permitted in specified depths (700–2,250 m), subject to quotas and monitoring. Management is overseen by the GSGSSI, headquartered in the , with enforcement via patrol vessels and collaboration with the for ecological monitoring, including seabird censuses and invasive species surveillance. Permits for scientific research, tourism, or fisheries are rigorously assessed to minimize environmental impact, with the MPA undergoing quinquennial scientific reviews to adapt regulations based on data from ongoing surveys. Terrestrial access restrictions extend to prohibiting non-essential activities, fostering a precautionary approach that balances conservation with limited sustainable resource use, though full no-take from environmental groups has not been implemented.

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