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 2,352 metres (7,717 ft).[1][2][3] They were the most northerly black smoker vents when they were discovered in mid-July 2008.[4]

Loki's Castle
An ROV samples fluids at Loki's Castle.
The top three feet of a vent chimney almost 40 feet (12 m) tall at Loki's Castle in mid-July 2008.
Map showing the location of Loki's Castle
Map showing the location of Loki's Castle
LocationMid-Atlantic Ridge
Coordinates73°33′00″N 08°09′00″W
Min. elevation−2,352 metres (−7,717 ft)

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 120 nautical miles (220 km) 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[3] (named after the Norwegian marine biologist Georg Ossian Sars[5] and launched in May 2003[6]). The vents were located using a remotely controlled undersea vehicle.[3]

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.[3] 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.[3] 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.[3]

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".[3]

2 metres (6.6 ft) gravity cores were collected from the vent field in 2010.[2][7]

Geology

Loki's Castle is located on the Gakkel Ridge (previously the Arctic Mid-Ocean Ridge), where the Mohns and Knipovich ridges converge.[2] 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.[8]

21 types of minerals have been identified at the vent field.[9] The chimneys are predominantly sphalerite, pyrite and pyrrhotite, and small amounts of chalcopyrite.[2] 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.[10]

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.[3] One of these, an archaeal phylum named Lokiarchaeota, was discovered and named after Loki's Castle.[11][12][7] The Lokiarchaeota is renowned as a potential linkage between prokaryotes and eukaryotes.[7]

The bristleworm Nicomache lokii (Maldanidae) is thought to be a key species in the fauna surrounding the hydrothermal vents in the area.[13] However, this species is only one of more than ten species newly discovered here.[14]

Melitidae amphipods, found around Loki's Castle.

Sclerolinum contortum tube worms are located at the field on the largest sulfide mounds.[2] 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.[15] Of 23 high-quality NCLDV genomic bins:

For example, the iridovirus-like gene sequence has been named "LCIVAC01".

See also

References
  1. "Arctic Circle Vent". University of Washington. 2008-07-24. Retrieved 2008-07-25.
  2. Pedersen, Rolf B.; Rapp, Hans Tore; Thorseth, Ingunn H.; Lilley, Marvin D.; Barriga, Fernando J. A. S.; Baumberger, Tamara; Flesland, Kristin; Fonseca, Rita; Früh-Green, Gretchen L.; Jorgensen, Steffen L. (23 November 2010). "Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge". Nature Communications. 1 (1): 126–. doi:10.1038/ncomms1124. PMC 3060606. PMID 21119639.
  3. "Scientists Break Record By Finding Northernmost Hydrothermal Vent Field". Science Daily. 2008-07-24. Retrieved 2008-07-25.
  4. "Boiling Hot Water Found in Frigid Arctic Sea". livescience.com. 2008-07-24. Retrieved 2008-07-25.
  5. "Background about the G.O. Sars". University of Bergen. Archived from the original on 2012-05-08. Retrieved 2008-07-25.
  6. "G.O. Sars". Norwegian Institute of Marine Research. Retrieved 2008-07-25.
  7. Spang, Anja; Saw, Jimmy H.; Jørgensen, Steffen L.; Zaremba-Niedzwiedzka, Katarzyna; Martijn, Joran; Lind, Anders E.; van Eijk, Roel; Schleper, Christa; Guy, Lionel; Ettema, Thijs J. G. (May 2015). "Complex archaea that bridge the gap between prokaryotes and eukaryotes". Nature. 521 (7551): 173–179. doi:10.1038/nature14447. PMC 4444528. PMID 25945739.
  8. Baumberger, Tamara; Früh-Green, Gretchen L.; Thorseth, Ingunn H.; Lilley, Marvin D.; Hamelin, Cédric; Bernasconi, Stefano M.; Okland, Ingeborg E.; Pedersen, Rolf B. (August 2016). "Fluid composition of the sediment-influenced Loki's Castle vent field at the ultra-slow spreading Arctic Mid-Ocean Ridge". Geochimica et Cosmochimica Acta. 187: 156–178. doi:10.1016/j.gca.2016.05.017.
  9. "Loki's Castle". Mindat. Hudson Institute of Mineralogy.
  10. Steen, Ida H.; Dahle, Håkon; Stokke, Runar; Roalkvam, Irene; Daae, Frida-Lise; Rapp, Hans Tore; Pedersen, Rolf B.; Thorseth, Ingunn H. (7 January 2016). "Novel Barite Chimneys at the Loki's Castle Vent Field Shed Light on Key Factors Shaping Microbial Communities and Functions in Hydrothermal Systems". Frontiers in Microbiology. 6: 1510. doi:10.3389/fmicb.2015.01510. PMC 4703759. PMID 26779165.
  11. Jorgensen, Steffen Leth; Hannisdal, Bjarte; Lanzén, Anders; Baumberger, Tamara; Flesland, Kristin; Fonseca, Rita; Øvreås, Lise; Steen, Ida H.; Thorseth, Ingunn H.; Pedersen, Rolf B.; Schleper, Christa (16 October 2012). "Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge". Proceedings of the National Academy of Sciences. 109 (42): E2846–E2855. doi:10.1073/pnas.1207574109. PMC 3479504. PMID 23027979.
  12. Jørgensen, Steffen L.; Thorseth, Ingunn H.; Pedersen, Rolf B.; Baumberger, Tamara; Schleper, Christa (2013). "Quantitative and phylogenetic study of the Deep Sea Archaeal Group in sediments of the Arctic mid-ocean spreading ridge". Frontiers in Microbiology. 4: 299. doi:10.3389/fmicb.2013.00299. PMC 3790079. PMID 24109477.
  13. Andreassen, Kim (24 September 2011). "Viktig og svovelkjær børstefyr". Archived from the original on 2011-09-24.
  14. Andreassen, Kim (25 August 2019). "Fant nye arter i Arktis". Universitetet i Bergen. Archived from the original on 2019-08-25.
  15. Bäckström, Disa; Yutin, Natalya; Jørgensen, Steffen L.; Dharamshi, Jennah; Homa, Felix; Zaremba-Niedwiedzka, Katarzyna; Spang, Anja; Wolf, Yuri I.; Koonin, Eugene V.; Ettema, Thijs J. G. (30 April 2019). "Virus Genomes from Deep Sea Sediments Expand the Ocean Megavirome and Support Independent Origins of Viral Gigantism". mBio. 10 (2): e02497–18. doi:10.1128/mBio.02497-18. PMC 6401483. PMID 30837339.
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