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The sub-Antarctic zone BAS: World’s largest iceberg grounds near sub-Antarctic Island of South Georgia Editorial guidelines – sub-Arctic is a physiographic region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region includes many islands in the southern parts of the Atlantic Ocean, Indian Ocean, and Pacific Ocean oceans, especially those situated north of the Antarctic Convergence. Subantarctic glaciers are, by definition, located on islands within the subantarctic region. All located on the continent of Antarctica are by definition considered to be Antarctic glaciers.
Another factor that contributes to the climate of the subantarctic region, though to a much lesser extent than the thermohaline circulation, is the formation of Antarctic Bottom Water (ABW) by halothermal dynamics. The halothermal circulation is that portion of the global ocean circulation that is driven by global created by surface heat and evaporation.
At between 51°–56° south of the Equator, the Falkland Islands, Isla de los Estados, Ildefonso Islands, Diego Ramírez Islands, and other islands associated with Tierra del Fuego and Cape Horn, lie north of the Antarctic Convergence in the region often referred to as the Roaring Forties. Unlike other subantarctic islands, these islands have tree line, temperate grasslands (mostly Poa flabellata), and even arable land. They also lack tundra and snow line and ice at their lowest elevations. Despite their more southerly location, it is debatable whether these islands should be considered as such because their climate and geography differs significantly from other subantarctic islands.
At between 52°–57° south of the Equator, the Campbell Islands, Heard Island and McDonald Islands, Bouvet Island, the South Georgia Group, Macquarie Island, and the South Sandwich Islands are also located in the Furious Fifties. The geography of these islands is characterized by tundra, permafrost, and . These islands are situated close to or south of the Antarctic Convergence, but north of 60° S latitude (the continental limit according to the Antarctic Treaty). Therefore, although some are located south of the Antarctic Convergence, they should still be considered as subantarctic islands by virtue of their location north of 60° S.
At between 60°–69° south of the Equator, in the region often referred to as the Roaring Forties, the South Orkney Islands, South Shetland Islands, Balleny Islands, Scott Island, and Peter I Island are all properly considered to be Antarctic islands for the following three reasons:
In light of the above considerations, the following should be considered to be subantarctic islands:
In addition to new land being produced by volcanism, global warming of the climate is causing the retreat of glaciers on the islands ( see section below ). These combined processes produce new ice-free terrestrial and freshwater , such as and , which are now available for colonization by plants and animals.
Heard Island has vast colonies of and , and large harems of land-based marine predators such as and . Due to the very high numbers of and on Heard Island, the area is considered a "biological hot spot". The marine environment surrounding the islands features diverse and distinctive Benthic zone that support a range of species including , , and . This marine environment also serves as a nursery area for a range of fishes, including some species of commercial interest.
Many subantarctic glaciers are also in retreat. Mass balance is significantly negative on many glaciers on Kergeulen Island, Heard Island, South Georgia and Bouvet Island.
Available records show no apparent change in glacier mass balance between 1874 and 1929. Between 1949 and 1954, marked changes were observed to have occurred in the ice formations above on the southwestern slopes of Big Ben, possibly as a result of volcanism. By 1963, major recession was obvious below on almost all glaciers, and minor recession was evident as high as .
Retreat of glacier fronts across Heard Island is evident when comparing aerial photographs taken in December 1947 with those taken on a return visit in early 1980. Retreat of Heard Island glaciers is most dramatic on the eastern section of the island, where the Glacier terminus of former tidewater glaciers are now located inland. Glaciers on the northern and western coasts have narrowed significantly, while the area of glaciers and on Laurens Peninsula have shrunk by 30% – 65%.
During the time period between 1947 and 1988, the total area of Heard Island's glaciers decreased by 11%, from 288 km2 (roughly 79% of the total area of Heard Island) to only 257 km2. A visit to the island in the spring of 2000 found that the Stephenson, Brown Glacier and Baudissin glaciers, among others, had retreated even further. The terminus of Brown Glacier has retreated approximately 1.1 kilometres since 1950. The total ice-covered area of Brown Glacier is estimated to have decreased by roughly 29% between 1947 and 2004. This degree of loss of glacier mass is consistent with the measured increase in temperature of +0.9 °C over that time span.
The coastal ice cliffs of Brown Glacier and Stephenson Glacier, which in 1954 were over high, had disappeared by 1963 when the glaciers terminated as much as inland. Baudissin Glacier on the north coast has lost at least , and Vahsel Glacier on the west coast has lost at least . Winston Glacier, which retreated approximately between 1947 and 1963, appears to be a very sensitive indicator of glacier change on the island. The young moraines flanking Winston Lagoon show that Winston Glacier has lost at least of ice within a recent time period.
The glaciers of Laurens Peninsula, whose maximum elevation is only 500 m above sea level, are smaller and shorter than most of the other Heard Island glaciers, and therefore much more sensitive to temperature effects. Accordingly, their total area has decreased by over 30 percent. Jacka Glacier on the east coast of Laurens Peninsula has also demonstrated marked recession since 1955. In the early 1950s, Jacka Glacier had receded only slightly from its position in the late 1920s, but by 1997 it had receded about 700 m back from the coastline.
Possible causes of glacier recession on Heard Island include:
The Australian Antarctic Division conducted an expedition to Heard Island during the austral summer of 2003–04. A small team of scientists spent two months on the island, conducting studies on Bird and terrestrial biology and glaciology. Glaciologists conducted further research on the Brown Glacier, in an effort to determine whether glacial retreat is rapid or punctuated. Using a portable Echo sounding, the team took measurements of the volume of the glacier. Monitoring of climatic conditions continued, with an emphasis on the impact of on glacier mass balance. Based on the findings of that expedition, the rate of loss of glacier ice on Heard Island appears to be accelerating. Between 2000 and 2003, repeat GPS Surveying revealed that the rate of loss of ice in both the ablation zone and the accumulation zone of Brown Glacier was more than double average rate measured from 1947 to 2003. The increase in the rate of ice loss suggests that the glaciers of Heard Island are reacting to ongoing climate change, rather than approaching dynamic equilibrium. The retreat of Heard Island's glaciers is expected to continue for the foreseeable future.
Antipodes Islands Pacific Ocean New Zealand Auckland Islands Pacific Ocean New Zealand Bounty Islands Pacific Ocean New Zealand Bouvet Island Atlantic Ocean Norway Campbell Islands Pacific Ocean New Zealand Crozet Islands ( or officially Archipel Crozet) Indian Ocean France Heard Island and McDonald Islands (HIMI) Indian Ocean Australia Kerguelen Islands Indian Ocean France Macquarie Island Pacific Ocean Australia Prince Edward Islands Indian Ocean South Africa South Georgia Group Atlantic Ocean The Crown South Sandwich Islands Atlantic Ocean United Kingdom Snares Islands Pacific Ocean New Zealand
Subantarctic glaciers
This is a list of in the subantarctic. This list includes one snow field (Murray Snowfield). Snow fields are not glaciers in the strict sense of the word, but they are commonly found at the accumulation zone or head of a glacier. For the purposes of this list, Antarctica is defined as any latitude further south than 60° (the continental limit according to the Antarctic Treaty).
Abbotsmith Glacier 4.8 km Heard Island Allison Glacier Heard Island Austin Glacier South Georgia Group Bary Glacier South Georgia Group Baudissin Glacier (2.8 km) Heard Island Bertrab Glacier "small" South Georgia Group Bogen Glacier "small" South Georgia Group Briggs Glacier South Georgia Group Brøgger Glacier 13 km South Georgia Group Brown Glacier Heard Island Brunonia Glacier South Georgia Group Buxton Glacier South Georgia Group Challenger Glacier Heard Island Christensen Glacier South Georgia Group Christensen Glacier Bouvet Island Christophersen Glacier South Georgia Group Clayton Glacier South Georgia Group Compton Glacier Heard Island Cook Glacier South Georgia Group Crean Glacier 6 km South Georgia Group Deacock Glacier Heard Island Dead End Glacier South Georgia Group Downes Glacier Heard Island Ealey Glacier Heard Island Eclipse Glacier South Georgia Group Esmark Glacier South Georgia Group Fiftyone Glacier Heard Island Fortuna Glacier South Georgia Group Geikie Glacier South Georgia Group Gotley Glacier 13.2 km Heard Island Graae Glacier 3.2 km South Georgia Group Grace Glacier South Georgia Group Hamberg Glacier South Georgia Group Harker Glacier South Georgia Group Harmer Glacier South Georgia Group Heaney Glacier South Georgia Group Helland Glacier South Georgia Group Henningsen Glacier South Georgia Group Herz Glacier South Georgia Group Hindle Glacier 10 km South Georgia Group Hodges Glacier South Georgia Group Horntvedt Glacier Bouvet Island Jacka Glacier 1.3 km Heard Island Jenkins Glacier South Georgia Group Jewell Glacier South Georgia Group Keilhau Glacier 8 km South Georgia Group Kjerulf Glacier South Georgia Group König Glacier South Georgia Group Lancing Glacier South Georgia Group Lewald Glacier South Georgia Group Lied Glacier Heard Island Lucas Glacier South Georgia Group Lyell Glacier South Georgia Group Mary Powell Glacier Heard Island Morris Glacier South Georgia Group Murray Snowfield South Georgia Group Nachtigal Glacier South Georgia Group Neumayer Glacier 13 km South Georgia Group Nordenskjöld Glacier "large" South Georgia Group Novosilski Glacier 13 km South Georgia Group Paget Glacier 6 km South Georgia Group Peters Glacier South Georgia Group Philippi Glacier South Georgia Group Posadowsky Glacier Bouvet Island Price Glacier South Georgia Group Purvis Glacier South Georgia Group Quensel Glacier "small" South Georgia Group Risting Glacier South Georgia Group Ross Glacier 10 km South Georgia Group Ryan Glacier South Georgia Group Salomon Glacier South Georgia Group Schmidt Glacier Heard Island Schrader Glacier South Georgia Group Spenceley Glacier South Georgia Group Stephenson Glacier Heard Island Storey Glacier South Georgia Group Twitcher Glacier 6 km South Georgia Group Tyrrell Glacier South Georgia Group Vahsel Glacier Heard Island Webb Glacier 3.2 km South Georgia Group Weddell Glacier 3.2 km South Georgia Group Wheeler Glacier 3.2 km South Georgia Group Winston Glacier Heard Island
Climate
Impact of climate change on SAMW
Together, the Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) act as a carbon sink, absorbing atmospheric carbon dioxide and storing it in solution. If the SAMW temperature increases as a result of climate change, the SAMW will have less capacity to store dissolved carbon dioxide. Research using a computerized climate system model suggests that if atmospheric carbon dioxide concentration were to increase to 860 ppm by the year 2100 (roughly double today's concentration), the SAMW will decrease in density and salinity. The resulting reductions in the subduction and transport capacity of SAMW and AAIW water masses could potentially decrease the absorption and storage of CO2 in the Southern Ocean.
Flora and fauna
The Antarctic realm and Antarctic Floristic Kingdom include most of the subantarctic islands native biota, with many endemism genus and species of flora and fauna.
Subantarctic island example
The physical landscape and biota communities of Heard Island and McDonald Islands are constantly changing due to volcanism, strong winds and waves, and climate change. Volcanic activity has been observed in this area since the mid-1980s, with fresh lava flows on the southwest flanks of Heard Island. Satellite imagery shows that McDonald Island increased in size from about 1 to 2.5 square kilometers between 1994 and 2004, as a result of volcanic activity.
Retreat of subantarctic glaciers
Glaciers are currently retreating at significant rates throughout the southern hemisphere. With respect to glaciers of the Andes mountains in South America, abundant evidence has been collected from ongoing research at Nevado del Ruiz in Colombia, Quelccaya Ice Cap and Qori Kalis Glacier in Peru, Zongo Glacier, Chacaltaya and Charquini glaciers in Bolivia, the Aconcagua River Basin in the central Chilean Andes, and the Northern Patagonian and Southern Patagonian . Retreat of glaciers in New Zealand and Antarctica is also well documented.
Glaciers of Heard Island
Heard Island is a heavily glacierized, subantarctic volcanic island located in the Southern Ocean, roughly 4000 kilometers southwest of Australia. 80% of the island is covered in ice, with glaciers descending from 2400 meters to sea level. Due to the steep topography of Heard Island, most of its glaciers are relatively thin (averaging only about 55 meters in depth). The presence of glaciers on Heard Island provides an excellent opportunity to measure the rate of glacial retreat as an indicator of climate change.
See also
Further reading
External links
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