The sub-Antarctic zoneBAS: World’s largest iceberg grounds near sub-Antarctic Island of South GeorgiaEditorial 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, Indian, and Pacific oceans, especially those situated north of the Antarctic Convergence. Subantarctic glaciers are, by definition, located on islands within the subantarctic region. All glaciers located on the continent of Antarctica are by definition considered to be Antarctic glaciers.
Geography The subantarctic region comprises two geographic zones and three distinct fronts. The northernmost boundary of the subantarctic region is the rather ill-defined Subtropical Front (STF), also referred to as the Subtropical Convergence. To the south of the STF is a geographic zone, the Subantarctic Zone (SAZ). South of the SAZ is the Subantarctic Front (SAF). South of the SAF is another marine zone, called the Polar Frontal Zone (PFZ). The SAZ and the PFZ together form the subantarctic region. The southernmost boundary of the PFZ (and hence, the southern border of the subantarctic region) is the Antarctic Convergence, located approximately 200 kilometers south of the Antarctic Polar Front (APF).
Influence of the Antarctic Circumpolar Current and thermohaline circulation
The subantarctic Front, found between 48°S and 58°S in the Indian and Pacific Ocean and between 42°S and 48°S in the Atlantic Ocean, defines the northern boundary of the Antarctic Circumpolar Current (or ACC). The ACC is the most important ocean current in the Southern Ocean, and the only current that flows completely around the Earth. Flowing eastward through the southern portions of the Atlantic, Indian, and Pacific Oceans, the ACC links these three otherwise separate oceanic basins. Extending from the sea surface to depths of 2000–4000 meters, and with a width of as great as 2000 kilometers, the ACC transports more water than any other ocean current. The ACC carries up to 150 Sverdrups (150 million cubic meters per second), equivalent to 150 times the volume of water flowing in all the world's rivers. The ACC and the global thermohaline circulation strongly influence regional and global climate as well as underwater biodiversity.
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 density gradients created by surface heat and evaporation.
Definition of subantarctic: political versus scientific
Several distinct water masses converge in the immediate vicinity of the APF or Antarctic Convergence (in particular the Subantarctic Surface Water (Subantarctic Mode Water or SAMW), Antarctic Surface Water, and the Antarctic Intermediate Water). This convergence creates a unique environment, noted for its very high marine productivity, especially for antarctic krill. Because of this, all lands and waters situated south of the Antarctic Convergence are considered to belong to the Antarctic from a climatological, biological and hydrological standpoint. However, the text of the Antarctic Treaty, article VI ("Area covered by Treaty") states: "The provisions of the present Treaty shall apply to the area south of 60° South latitude". Therefore, Antarctica is defined from a political standpoint as all land and ice shelves south of 60°S latitude.
Subantarctic islands
At between about 46°–50° south of the Equator, in the region often referred to as the Roaring Forties, are the Crozet Islands, the Prince Edward Islands, Wager Island, the Bounty Islands, the Snares Islands, the Kerguelen Islands, the Antipodes Islands, and the Auckland Islands. The geography of these islands is characterized by tundra, with some trees on the Snares Islands and the Auckland Islands. These islands are all located near the Antarctic Convergence (with the Kerguelen Islands south of the Convergence) and are properly considered to be subantarctic islands.
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 Furious Fifties. Unlike other subantarctic islands, these islands have trees, temperate grasslands (mostly tussac grass), and even arable land. They also lack tundra and permanent snow 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 Island Group, 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 volcanoes. 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 Shrieking Sixties, 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:
they are all located south of the Antarctic Convergence they are all located within the Southern (or Antarctic) Ocean they are all located south of the 60th parallel south
In light of the above considerations, the following should be considered to be subantarctic islands:
Name Coordinates Ocean Administered by Antipodes Islands Pacific Ocean New Zealand Auckland Islands Pacific Ocean New Zealand Bounty Islands Pacific Ocean New Zealand Bouvet Island (Bouvetøya) Atlantic Ocean Norway Campbell Island Group 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 United Kingdom South Sandwich Islands Atlantic Ocean United Kingdom Snares Islands Pacific Ocean New Zealand
Subantarctic glaciers
This is a list of glaciers 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).
Name of Glacier Coordinates Length or (Width) Location 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 endemic genera 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.