The Gakkel Ridge (formerly known as the Nansen Cordillera and Arctic Mid-Ocean Ridge) [1] is a mid-oceanic ridge, a divergent tectonic plate boundary between the North American Plate and the Eurasian Plate. [2] It is located in the Eurasian Basin of the Arctic Ocean, between Greenland and Siberia. Geologically, it connects the northern end of the Mid-Atlantic Ridge with the Laptev Sea Rift.
The existence and approximate location of the Gakkel Ridge were predicted by Soviet polar explorer Yakov Yakovlevich Gakkel and confirmed on Soviet expeditions in the Arctic around 1950. The Ridge is named after him, and the name was recognized in April 1987 by SCUFN (under that body's old name, the Sub-Committee on Geographical Names and Nomenclature of Ocean Bottom Features). [1]
Until 1999, it was believed to be non-volcanic; that year, scientists operating from a nuclear submarine discovered active volcanoes along it. The largest, the Gakkel Ridge Caldera, is a supervolcano that erupted approximately 1.1 million years ago during the Pleistocene. [3] In 2001 two research icebreakers, the German Polarstern and the American Healy , with several groups of scientists, cruised to the Gakkel Ridge to explore it and collect petrological samples. Among other discoveries, this expedition found evidence of hydrothermal vents. In 2007, Woods Hole Oceanographic Institution conducted the "Arctic Gakkel Vents Expedition" (AGAVE), which made some unanticipated discoveries, including the unconsolidated fragmented pyroclastic volcanic deposits that cover the axial valley of the ridge (whose area is greater than 10 km2). These suggest volatile substances in concentrations ten times those in the magmas of normal mid-ocean ridges. [4] Using "free-swimming" robotic submersibles on the Gakkel ridge, the AGAVE expedition also discovered what they called "bizarre 'mats' of microbial communities containing a half dozen or more new species". [5] A hydrothermal site, named "Aurora", was discovered in 2014. [6] [7] Aurora has elevated levels of methane and high temperatures, suggesting interactions between water and ultramafic rock below the vent field (rather than basalt reactions). Aurora's geochemistry may resemble that of the Rainbow Vent Field in the Atlantic Ocean.
The Gakkel Ridge is approximately 1,800 kilometres (1,100 mi) long and is the slowest known spreading ridge on earth, with a rate of less than one centimeter per year. It continues to the south and connects with the Knipovich Ridge. [8]
The Gakkel ridge is not offset by any transform faults. The ridge does have segments with variable orientation and varying degrees of volcanism: the Western Volcanic Zone From the Lena trough (7° W, to 3° E longitude), the Sparsely Magmatic Zone (from 3° E to 29° E longitude), and the Eastern Magmatic Zone (from 29° E to 89°E). [9] The gaps of volcanic activity imply very cold crust and mantle, probably related to the very low spreading rate, but it is not yet known why some parts of the ridge are more magmatic than others. [10] Some earthquakes have been detected from the mantle, below the crust, which is very unusual for a mid-ocean ridge. [11] It confirms that the mantle and crust of Gakkel ridge, like some segments of the Southwest Indian Ridge, are very cold.
The Gakkel ridge features several confirmed and inferred hydrothermal fields, including Aurora (visually confirmed in 2014) and Lucky B (dredged in 2001). [12] [13] [14] More sites have been inferred, but not confirmed due to difficulties with ice at higher latitudes.
Hydrothermal circulation in its most general sense is the circulation of hot water. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. In general, this occurs near volcanic activity, but can occur in the shallow to mid crust along deeply penetrating fault irregularities or in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism. Hydrothermal circulation often results in hydrothermal mineral deposits.
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.
The Lost City Hydrothermal Field, often referred to simply as Lost City, is an area of marine alkaline hydrothermal vents located on the Atlantis Massif at the intersection between the Mid-Atlantic Ridge and the Atlantis Transform Fault, in the Atlantic Ocean. It is a long-lived site of active and inactive ultramafic-hosted serpentinization, abiotically producing many simple molecules such as methane and hydrogen which are fundamental to microbial life. As such it has generated scientific interest as a prime location for investigating the origin of life on Earth and other planets similar to it.
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin.
A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of them result from tensional forces, caused by a process known as oceanic trench rollback, where a subduction zone moves towards the subducting plate. Back-arc basins were initially an unexpected phenomenon in plate tectonics, as convergent boundaries were expected to universally be zones of compression. However, in 1970, Dan Karig published a model of back-arc basins consistent with plate tectonics.
The Izu–Bonin–Mariana (IBM) arc system is a tectonic plate convergent boundary in Micronesia. The IBM arc system extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, the Bonin Islands, and the Mariana Islands; much more of the IBM arc system is submerged below sealevel. The IBM arc system lies along the eastern margin of the Philippine Sea Plate in the Western Pacific Ocean. It is the site of the deepest gash in Earth's solid surface, the Challenger Deep in the Mariana Trench.
An oceanic core complex, or megamullion, is a seabed geologic feature that forms a long ridge perpendicular to a mid-ocean ridge. It contains smooth domes that are lined with transverse ridges like a corrugated roof. They can vary in size from 10 to 150 km in length, 5 to 15 km in width, and 500 to 1500 m in height. Their counterparts on land are metamorphic core complexes, which form in areas of continental crustal extension or stretching.
The Molloy Deep is a bathymetric feature in the Fram Strait, within the Greenland Sea east of Greenland and about 160 km (100 mi) west of Svalbard. It is the location of the deepest point in the Arctic Ocean. The Molloy Deep, Molloy Hole, Molloy Fracture Zone, and Molloy Ridge were named after Arthur E. Molloy, a U.S. Navy research scientist who worked in the North Atlantic, North Pacific, and Arctic Oceans in the 1950s–1970s.
The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate to the south, the SWIR is characterised by ultra-slow spreading rates (only exceeding those of the Gakkel Ridge in the Arctic) combined with a fast lengthening of its axis between the two flanking triple junctions, Rodrigues (20°30′S70°00′E) in the Indian Ocean and Bouvet (54°17′S1°5′W) in the Atlantic Ocean.
Loki's Castle is a field of five active hydrothermal vents in the mid-Atlantic Ocean, located at 73 degrees north on the Mid-Atlantic Ridge between Iceland and Svalbard at a depth of 2,352 metres (7,717 ft). When they were discovered in mid-July 2008, they were the most northerly black smoker vents.
The Fram Strait is the passage between Greenland and Svalbard, located roughly between 77°N and 81°N latitudes and centered on the prime meridian. The Greenland and Norwegian Seas lie south of Fram Strait, while the Nansen Basin of the Arctic Ocean lies to the north. Fram Strait is noted for being the only deep connection between the Arctic Ocean and the World Oceans. The dominant oceanographic features of the region are the West Spitsbergen Current on the east side of the strait and the East Greenland Current on the west.
InterRidge is a non-profit organisation that promotes interdisciplinary, international studies in the research of oceanic spreading centres, including mid-ocean ridge and back-arc basin systems. It does so by creating a global research community, planning and coordinating new science programmes that no single nation can achieve alone, exchanging scientific information, and sharing new technologies and facilities. InterRidge is dedicated to reaching out to the public, scientists and governments, and to providing a unified voice for ocean ridge researchers worldwide.
The Troodos Ophiolite on the island of Cyprus represents a Late Cretaceous spreading axis that has since been uplifted due to its positioning on the overriding Anatolian plate at the Cyprus arc and ongoing subduction to the south of the Eratosthenes Seamount.
The Beebe Hydrothermal Vent Field is the world's deepest known hydrothermal vent site and is located just south of Grand Cayman in the Caribbean, on the north side of the Mid-Cayman Spreading Centre in the Cayman Trough. Approximately 24 kilometres (15 mi) south of Beebe is the Von Damm Vent Field.
An upper mantle body is a geological region where upper mantle rocks (peridotite) outcrop on the surface of the Earth.
Kenneth Craig Macdonald is an American oceanographer and marine geophysicist born in San Francisco, California in 1947. As of 2018 he is professor emeritus at the Department of Earth Science and the Marine Sciences Institute at the University of California, Santa Barbara (UCSB). His work focuses on the tectonics and geophysics of the global mid-oceanic ridge including its spreading centers and transform faults, two of the three types of plate boundaries central to the theory of plate tectonics. His work has taken him to the north and south Atlantic oceans, the north and south Pacific oceans, the Indian Ocean, the Red Sea and the Sea of Cortez, as well as to the deep seafloor on over 50 dives in the research submersible ALVIN. Macdonald has participated in over 40 deep sea expeditions, and was chief- or co-chief scientist on 31 expeditions.
Susan Humphris is a geologist known for her research on processes at mid-ocean ridges. She is an elected fellow of the American Geophysical Union.
Rachel Haymon is a marine geologist known for her work linking geological and biological processes occurring at deep-sea hydrothermal vents. In 2005 she was elected a fellow of the Geological Society of America.
Margo Helen Edwards is a marine geologist known for mapping of the seafloor and hydrothermal vents. She led the 1999 SCICEX and was the first women to live aboard a United States' Navy submarine while doing under-ice research.
The Mohns Ridge is an ultraslow-spreading segment of the Mid-Atlantic Ridge located to the north of Jan Mayen in the Arctic Ocean. It is bounded to the south by the Jan Mayen fracture zone, and transitions to Knipovich Ridge in the north-east.
| Present |  | |
|---|---|---|
| Former | ||
| International | |
|---|---|
| National | |
