Loki's Castle

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. The field resides approximately {{convert|2300|m}} deep at the boundary of the Greenland and Norwegian Sea.

File:G O SARS Bergen Norway 2009.jpg.]]

The vents were discovered in 2008 by a 25-person multinational scientific expedition of the University of Bergen, Norway. The vents are located more than {{convert|120|nmi|km}} north of what were previously the northernmost known vents, discovered in 2005. The high-latitude 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).{{cite web |url=http://www.uib.no/forskningsfartoy/english/background/index.html |title=Background about the G.O. Sars |accessdate=2008-07-25 |publisher=University of Bergen |archive-url=https://web.archive.org/web/20120508064933/http://www.uib.no/forskningsfartoy/english/background/index.html |archive-date=2012-05-08 |url-status=dead }}{{cite web |url=http://www.imr.no/english/about_imr/vessels/g.o._sars |title=G.O. Sars |accessdate=2008-07-25 |publisher=Norwegian Institute of Marine Research}} The vents were located using a remotely controlled underwater vehicle.

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".

{{convert|2|m|ft}} gravity cores were collected from the vent field in 2010.{{cite journal |last1=Spang |first1=Anja |last2=Saw |first2=Jimmy H. |last3=Jørgensen |first3=Steffen L. |last4=Zaremba-Niedzwiedzka |first4=Katarzyna |last5=Martijn |first5=Joran |last6=Lind |first6=Anders E. |last7=van Eijk |first7=Roel |last8=Schleper |first8=Christa |last9=Guy |first9=Lionel |last10=Ettema |first10=Thijs J. G. |title=Complex archaea that bridge the gap between prokaryotes and eukaryotes |journal=Nature |date=May 2015 |volume=521 |issue=7551 |pages=173–179 |doi=10.1038/nature14447|pmid=25945739 |pmc=4444528 }}

The field was revisited by the G.O. Sars in 2018 and 2019 by the United States Geological Survey and the University of Bergen to take sediment push cores.{{cite journal |last1=Gartman |first1=A. |last2=Payan |first2=D. |last3=Au |first3=M. |last4=Reeves |first4=E. P. |last5=Jamieson |first5=J. W. |last6=Gini |first6=C. |last7=Roerdink |first7=D. |title=Hydrothermal Plume Fallout, Mass Wasting, and Volcanic Eruptions Contribute to Sediments at Loki's Castle Vent Field, Mohns Ridge |journal=Geochemistry, Geophysics, Geosystems |date=February 2024 |volume=25 |issue=2 |doi=10.1029/2023GC011094|doi-access=free }}

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.{{cite journal |last1=Baumberger |first1=Tamara |last2=Früh-Green |first2=Gretchen L. |last3=Thorseth |first3=Ingunn H. |last4=Lilley |first4=Marvin D. |last5=Hamelin |first5=Cédric |last6=Bernasconi |first6=Stefano M. |last7=Okland |first7=Ingeborg E. |last8=Pedersen |first8=Rolf B. |title=Fluid composition of the sediment-influenced Loki's Castle vent field at the ultra-slow spreading Arctic Mid-Ocean Ridge |journal=Geochimica et Cosmochimica Acta |date=August 2016 |volume=187 |pages=156–178 |doi=10.1016/j.gca.2016.05.017}}

21 types of minerals have been identified at the vent field.{{cite web |title=Loki's Castle |url=https://www.mindat.org/loc-232854.html |website=Mindat |publisher=Hudson Institute of Mineralogy}} When cores were collected in 2018 and 2019, talc was found in samples.{{cite news |last1=Cowing |first1=Keith |title=Arctic Mid-Ocean Ridge Sediment Cores Shed Light On Past Hydrothermal Activity |url=https://astrobiology.com/2024/03/arctic-mid-ocean-ridge-sediment-cores-shed-light-on-past-hydrothermal-activity.html |work=Astrobiology |date=13 March 2024}}

Carbon-14 dating estimates the oldest hydrothermal material at the field to be over 9,100 years old.

The vent field is composed of two {{convert|20-30|m}} sulfide mounds, each {{convert|150-200|m}} across, and join into a single composite mound. The size is comparable to that of the TAG field on the Mid-Atlantic Ridge, one of the largest known hydrothermal fields as of 2010. 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 five active chimneys of Loki's Castle are venting water as hot as {{Convert|320|C}} and sit on a vast mound of sulfide minerals that is about {{Convert|825|ft|m|order=flip}} in diameter at its base and some {{Convert|90|m|abbr=on}} across its top. The active chimneys are mostly black in colour but are covered with mats of white bacteria that are living on minerals and materials emitted by the vents. The older chimneys are mottled red in colour due to the presence of deposits of oxidised iron.

Four distinct high-temperature chimneys were sampled between 2008 and 2009: João, Menorah, Camel, and Sleepy. The chimneys are predominantly sphalerite, pyrite, and pyrrhotite, and small amounts of chalcopyrite. Small barite chimneys (height of <{{convert|1|m}}) are located east of the main field, where venting is less pronounced.{{cite journal |last1=Steen |first1=Ida H. |last2=Dahle |first2=Håkon |last3=Stokke |first3=Runar |last4=Roalkvam |first4=Irene |last5=Daae |first5=Frida-Lise |last6=Rapp |first6=Hans Tore |last7=Pedersen |first7=Rolf B. |last8=Thorseth |first8=Ingunn H. |title=Novel Barite Chimneys at the Loki's Castle Vent Field Shed Light on Key Factors Shaping Microbial Communities and Functions in Hydrothermal Systems |journal=Frontiers in Microbiology |date=7 January 2016 |volume=6 |page=1510 |doi=10.3389/fmicb.2015.01510|pmid=26779165 |pmc=4703759 |doi-access=free }} This section of the system is nicknamed the Barite Field.

Loki's Castle fluids are rich in volatile gases, namely hydrogen sulfide, hydrogen, and methane. The field is also associated with high concentrations of hydrocarbons, ammonium, and alkalinity while being depleted of dissolved iron and manganese. Fluid pH from high-temperature locations are acidic, ranging from 5.5 - 6.1.

File:Abludomelita obtusata.jpg

The bristleworm Nicomache lokii (Maldanidae) is thought to be a key species in the fauna surrounding the hydrothermal vents in the area.{{cite web |last1=Andreassen |first1=Kim |title=Viktig og svovelkjær børstefyr |url=http://www.forskning.no/artikler/2011/august/296350 |date=24 September 2011|archive-url=https://web.archive.org/web/20110924181936/http://www.forskning.no/artikler/2011/august/296350 |archive-date=2011-09-24 }} This species is one of the more than ten species that were newly discovered here.{{cite web |last1=Andreassen |first1=Kim |title=Fant nye arter i Arktis |url=https://www.uib.no/ka/51212/fant-nye-arter-i-arktis |publisher=Universitetet i Bergen |date=25 August 2019|archive-url=https://web.archive.org/web/20190825221310/https://www.uib.no/ka/51212/fant-nye-arter-i-arktis |archive-date=2019-08-25 }}

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.

Loki's Castle has dense mats of bacteria on and around vents that use the minerals and compounds expelled by the vents. Common among these are Epsilonproteobacteria and Gammaproteobacteria, which oxidize the abundant hydrogen and hydrogen sulfide and form biofilms on active chimney surfaces. Thaumarchaeota have been found at less active chimney sites. Sulfurovum dominate microbial mats. Samples from 2008 and 2010 contained a diversity of Chlamydiae.{{cite news |last1=Georgiou |first1=Aristos |title=Never-before-seen Species of Chlamydia Bacteria Found Below Arctic Ocean |url=https://www.newsweek.com/new-chlamydia-bacteria-deep-below-arctic-ocean-1491207 |work=Newsweek |date=9 March 2020 |language=en}}

Preliminary observations have indicated that the warm area around the vents of Loki's Castle is a marine ecotope populated with apparently unique and diverse microorganisms, unlike other observed marine hydrothermal vent ecosystems. One of these, an archaeal phylum named Lokiarchaeota, was discovered and named after Loki's Castle.{{cite journal |last1=Jorgensen |first1=Steffen Leth |last2=Hannisdal |first2=Bjarte |last3=Lanzén |first3=Anders |last4=Baumberger |first4=Tamara |last5=Flesland |first5=Kristin |last6=Fonseca |first6=Rita |last7=Øvreås |first7=Lise |last8=Steen |first8=Ida H. |last9=Thorseth |first9=Ingunn H. |last10=Pedersen |first10=Rolf B. |last11=Schleper |first11=Christa |title=Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge |journal=Proceedings of the National Academy of Sciences |date=16 October 2012 |volume=109 |issue=42 |pages=E2846–E2855 |doi=10.1073/pnas.1207574109|pmid=23027979 |pmc=3479504 |doi-access=free }}{{cite journal |last1=Jørgensen |first1=Steffen L. |last2=Thorseth |first2=Ingunn H. |last3=Pedersen |first3=Rolf B. |last4=Baumberger |first4=Tamara |last5=Schleper |first5=Christa |title=Quantitative and phylogenetic study of the Deep Sea Archaeal Group in sediments of the Arctic mid-ocean spreading ridge |journal=Frontiers in Microbiology |date=2013 |volume=4 |page=299 |doi=10.3389/fmicb.2013.00299|pmid=24109477 |pmc=3790079 |doi-access=free }}{{cite news |last1=Martin |first1=Alexander |title=Weird ARCHAEAN LIFE FORM found at 'Loki's Castle' DEEP beneath Arctic Circle |url=https://www.theregister.com/2015/05/07/boffins_bridge_the_gap_in_cellular_evolution_from_the_bottom_of_the_ocean/ |agency=The Register |publisher=situation publishing |date=7 May 2015}} Lokiarchaeota is renowned as a potential linkage between prokaryotes and eukaryotes in the three-domain system of life.

Metagenome analyses by Bäckström et al. in 2019 showed that there must be a whole series of previously unknown viruses that are 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.{{cite journal |last1=Bäckström |first1=Disa |last2=Yutin |first2=Natalya |last3=Jørgensen |first3=Steffen L. |last4=Dharamshi |first4=Jennah |last5=Homa |first5=Felix |last6=Zaremba-Niedwiedzka |first6=Katarzyna |last7=Spang |first7=Anja |last8=Wolf |first8=Yuri I. |last9=Koonin |first9=Eugene V. |last10=Ettema |first10=Thijs J. G. |title=Virus Genomes from Deep Sea Sediments Expand the Ocean Megavirome and Support Independent Origins of Viral Gigantism |journal=mBio |date=30 April 2019 |volume=10 |issue=2 |pages=e02497–18 |doi=10.1128/mBio.02497-18|pmid=30837339 |pmc=6401483 }} Of the 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

The iridovirus-like gene sequence has been named "LCIVAC01".

• Asgard (archaea)
• Lokiarchaeota

{{reflist}}

• Sandra Hines, [http://www.eurekalert.org/pub_releases/2008-07/uow-sbr072408.php Scientists break record by finding northernmost hydrothermal vent field], University of Washington Press Release, 24 July 2008.
• [http://www.geobio.uib.no/View.aspx?mid=1062&itemid=90&pageid=1093&moduledefid=71 2008 University of Bergen Expedition Journal for Day 17 (15 July 2008)], describing the moment of discovery.
• [http://www.geobio.uib.no/Default.aspx?pageid=1092 Photographs of the 2008 University of Bergen Expedition team members]
• [http://www.geobio.uib.no/Default.aspx?pageid=792 Background information about hydrothermal fields] (provided by the Centre for Geobiology, University of Bergen)
• [http://www.interridge.org/irvents/content/lokis-castle Loki's Castle], InterRidge Vents Database

Category:Hydrothermal vents

Category:Volcanoes of the Atlantic Ocean