Subantarctic

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 s, showing the Antarctic Circumpolar Current (ACC). In addition to the global thermohaline circulation, the ACC strongly influences regional and global climate. strongly influences regional and global climate. Blue paths represent deep-water currents, while red paths represent surface currents. 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 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 es in the Southern Ocean. 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 and surrounding islands in relation to the Antarctic Convergence and the 60th parallel south , 55°S. 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). For the purposes of this list, Antarctica is defined as any latitude further south than 60° (the continental limit according to the Antarctic Treaty). . Cape Arkona is seen on the left side of the image, with Lied Glacier just above and Gotley Glacier just below. Big Ben Volcano and Mawson Peak are seen at the lower right side of the image. : Harker Glacier, Cumberland Bay, Thatcher Peninsula, Allardyce Range, Mount Paget. , Cumberland West Bay, South Georgia, circa 1882–1883. , Cumberland West Bay, South Georgia, circa 1882–1883. , Cumberland Bay, South Georgia. ==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. 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 ecoregions, such as moraines and lagoons, which are now available for colonization by plants and animals. Heard Island has vast colonies of penguins and petrels, and large harems of land-based marine predators such as elephant seals and fur seals. Due to the very high numbers of seabirds and marine mammals on Heard Island, the area is considered a "biological hot spot". The marine environment surrounding the islands features diverse and distinctive benthic habitats that support a range of species including corals, sponges, barnacles and echinoderms. This marine environment also serves as a nursery area for a range of fishes, including some species of commercial interest. ==Retreat of subantarctic glaciers==

from 1990 to 2000. San Quintín Glacier is shown in the background 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, Chacaltaya and Charquini glaciers in Bolivia, the Aconcagua River Basin in the central Chilean Andes, and the Northern Patagonian and Southern Patagonian ice fields. Retreat of glaciers in New Zealand and Antarctica is also well documented. 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. 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. 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 termini of former tidewater glaciers are now located inland. 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 surface surveys 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. ==See also==