HR: 08:05h
AN: OS21C-01 INVITED     [Abstracts]
TI: Two Vent Fields Discovered at the Ultraslow Spreading Arctic Ridge System
AU: * Pedersen, R B
EM: rolf.pedersen@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007 Norway
AU: Thorseth, I H
EM: ingunn.thorseth@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007 Norway
AU: Hellevang, B
EM: bjarte.hellevang@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007 Norway
AU: Schultz, A
EM: adam@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin Building, Corvallis, OR 97331-5503 United States
AU: Taylor, P
EM: phil@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin Building, Corvallis, OR 97331-5503 United States
AU: Knudsen, H P
EM: hans.petter.knudsen@imr.no
AF: Institute of Marine Research, PB 1870 Nordnes, Bergen, 5817 Norway
AU: Steinsbu, B O
EM: bjorn.steinsbu@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007 Norway
AB: Two high-temperature vent fields were discovered at the Mohns Ridge during an expedition with the Norwegian research vessel "G.O. Sars" in July 2005. Both vent fields are located within the southernmost segment of the Mohns Ridge approximately 50 km north of the West Jan Mayen Fracture Zone. Water depths along this segment range from 3800 meters close to the fracture zone to ~500 meters at the segment centre where the vent fields are located. The largest field - named "Gallionella Garden" - is situated within a rift graben where high- and low-temperature venting occurs along ridge-parallel normal faults and fissures. Presently we have documented high- and low-temperature venting along more then 2 km of the fault and fissure system in the area. The high-temperature venting takes place at around 550 mbsl at the base of a 100 meter high fault wall and was traced ~500 meters along strike. The field consists of at least 10 major vent sites, each composed of multiple chimneys that are up to 5-10 meters tall. There are also large areas of diffuse flow. The temperature of the vent fluids was measured to be above 260§C at a chimney orifice. This is at the boiling point of seawater at these water depths, and gas bubbling was observed at several of the vent sites. A sample of the top of a chimney consists of anhydrite, barite, sphalerite and pyrite. Outside the high-temperature vent area mounds of ferric iron are abundant. Such deposits have presently been traced along ~2 km of the faults and fissure system in the area. The deposits are predominantly made up of branching and twisted stalks comparable to those formed by the iron oxidizing bacteria Gallionella ferruginea showing that the precipitation is mediated by microbial activity. The temperatures below the upper crust of a mound were measured to be one degree above the ambient water temperature. The Fe-oxyhydroxides show Nd-isotope compositions similar to the basaltic crust and Sr-isotope compositions close to that of seawater, and may have formed from fluids composed of 90 percent seawater and 10 percent of an end-member hydrothermal fluid. Nd-concentrations suggest Fe-precipitate/fluid ratio of one to a million (ie. that 1 kg of Fe-deposits scavenged neodymium from one million litres of fluids). A second vent field was discovered 5 km southwest of "Gallionella Garden" at ~700 mbsl. The "Soria Moria" field is located at a volcanic ridge composed of recent lava flows and is about 100 meters across. The field consists of numerous chimneys emitting buoyant white smoker fluids, as well as irregular shaped mounds with flange structures discharging fluids of higher density then the ambient waters. White bacterial mats cover the seafloor and chimneys at both fields, and shrimp, sea spiders and colonies of sea anemones, crinoids and hydroids are associated with the vent fields. The hydrothermal plumes were detected acoustically using the exceptionally sensitive scientific echo sounders on "G.O.Sars". The acoustic backscatters images show that the hydrothermal plume above "Gallionella Garden" perturb the upper hydrographical layers, implying that this shallow vent field may "fertilize" the productive hydrographical layers in the area.
UR: http://www.interridge.org/sciencewriteratsea/norway2005/index.html
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005