Loki's Castle

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 . They were the most northerly black smoker vents when they were discovered in mid-July 2008.
They are of geological interest as they occur in a relatively stable region of the Earth's crust, one with diminished tectonic forces and consequently fewer hydrothermal vents. They are the host site of a biologically distinct archaea, the Lokiarchaeota.
Discovery
The vents were discovered by a 25-person multinational scientific expedition of the University of Bergen, Norway, more than north of what were previously the northernmost known, discovered in 2005. The 2005 and 2008 expeditions were both led by geologist Rolf Pedersen of the university's Centre for Geobiology, aboard the research vessel G.O. Sars (named after the Norwegian marine biologist Georg Ossian Sars and launched in May 2003). The vents were located using a remotely controlled undersea vehicle.
Activity
The five active chimneys of Loki's Castle are venting water as hot as 320 °C (570 °F) and sit on a vast mound of sulfide minerals which is about 825 ft (250 m) in diameter at its base, and some 300 feet (90 m) across its top. A member of the 2008 expedition, oceanographer Marvin Lilley, has speculated that this may be the largest such deposit ever seen on the sea floor. The active chimneys are mostly black in colour, but are covered with mats of white bacteria which are living on minerals and materials emitted by the vents. The older chimneys are a mottled red colour, due to the presence of deposits of oxidised iron.
The vent field was given the name Loki's Castle as its shape reminded its discoverers of a fantasy castle. The reference is to the ancient Norse god of trickery, Loki. It was felt to be "an appropriate name for a field that was so difficult to locate".
gravity cores were collected from the vent field in 2010.
Geology
Loki's Castle is located on the Gakkel Ridge (previously the Arctic Mid-Ocean Ridge), where the Mohns and Knipovich ridges converge. Ocean core complexes are found to the northwest.
Loki's Castle is described in literature as a sediment-influenced basalt-hosted hydrothermal field. Due to boron isotopic composition of hydrothermal fluids, it is suggested that vent fluid is recharged (or percholates into the seafloor) in regions densely concentrated with oceanic sediments, rather than unsedimented igneous rock of ridge flanks.
21 types of minerals have been identified at the vent field. The chimneys are predominantly sphalerite, pyrite and pyrrhotite, and small amounts of chalcopyrite. Small barite chimneys are in the vicinity of the main field, where venting is less pronounced.
Fluid chemistry
Loki's Castle fluids are rich in volatile gases, namely hydrogen sulfide, hydrogen, and methane.
Ecology
Loki's Castle has dense mats of bacteria which utilize minerals and compounds expelled by the vents. Preliminary observations have indicated that the warm area around the vents of Loki's Castle is a marine ecotope populated with diverse and apparently unique microorganism vent fauna of microorganisms, unlike ecosystems around marine hydrothermal vents observed elsewhere. One of these, an archaeal phylum named Lokiarchaeota, was discovered and named after Loki's Castle. The Lokiarchaeota is renowned as a potential linkage between prokaryotes and eukaryotes.
The bristleworm Nicomache lokii (Maldanidae) is thought to be a key species in the fauna surrounding the hydrothermal vents in the area. However, this species is only one of more than ten species newly discovered here.
Sclerolinum contortum tube worms are located at the field on the largest sulfide mounds. Melitidae amphipods are found amongst the tube worms and are common in chimney crevices.
Metagenome analyses by Bäckström et al. showed in 2019 that there must be a whole series of previously unknown viruses known as LCVs or Loki's Castle Viruses. These are primarily giant viruses of the Megaviricetes class in the phylum Nucleocytoviricota - NCLDV) in the area of Loki's Castle. Of 23 high-quality NCLDV genomic bins:
15 are related to pithoviruses,
5 are related to Marseille viruses,
1 are related to iridoviruses and
2 are related to klosneuviruses
For example, the iridovirus-like gene sequence has been named "LCIVAC01".
See also
Asgard (archaea)
Lokiarchaeota
References
External links
Sandra Hines, Scientists break record by finding northernmost hydrothermal vent field, University of Washington Press Release, 24 July 2008.
2008 University of Bergen Expedition Journal for Day 17 (15 July 2008), describing the moment of discovery.
Photographs of the 2008 University of Bergen Expedition team members
Background information about hydrothermal fields (provided by the Centre for Geobiology, University of Bergen)
Loki's Castle, InterRidge Vents Database
Hydrothermal vents
Volcanoes of the Atlantic Ocean