HR: 12:05h
AN: OS22A-08    [Abstracts]
TI: Fluid flow rate, temperature and heat flux at Mohns Ridge vent fields: evidence from isosampler measurements for phase separated hydrothermal circulation along the arctic ridge system
AU: * Schultz, A
EM: adam@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg. Oregon State University, Corvallis, OR 97331-5503 United States
AU: Pedersen, R B
EM: Rolf.Pedersen@geo.uib.no
AF: Institutt for geovitenskap, Realfagbygget, Allegt. 41, Bergen, 5007 Norway
AU: Thorseth, I H
EM: Ingunn.Thorseth@geo.uib.no
AF: Institutt for geovitenskap, Realfagbygget, Allegt. 41, Bergen, 5007 Norway
AU: Taylor, P
EM: phil@coas.oregonstate.edu
AF: School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff, CF10 3YE United Kingdom
AU: Flynn, M
EM: mflynn@mail.arc.nasa.gov
AF: NASA Ames Research Center, MS 239-15, Moffett Field, CA 94035 United States
AB: An expedition to the Mohns Ridge in the Norwegian-Greenland sea was carried out in July-August 2005 as part of BIODEEP, lead by University of Bergen (UoB). UoB had previously detected water column methane along this very slow spreading ridge. Previous ROV observations along the ridge (71 deg 18'N, 5 deg 47'W, 605 mbsl) near Jan Mayen had uncovered a broad area of ferric hydroxide-rich bacterial/mineral assemblages, comprising large populations of gallionella bacteria. This area was revisted in 2005. Characteristic of sections of this area ("Gallionella Garden") are chimney-like structures standing ~15 cm tall, often topped by a sea lily (heliometra glacialis). The interior of the structures comprised quasi-concentric bands with vertically-oriented channels. The Oregon State University/Cardiff University Isosampler sensor determined that some of these assemblages support fluid flow through their interior. The outflow from the chimney structures was typically +0.5 deg C, against background temperatures of -0.3 deg C. Flow anomalies were also identified atop extensive bacterial mats. Gallionella Gardens is several km in extent with active, albeit extremely low temperature hydrothermal flow. A field of active high temperature smoker chimney structures was located near Gallionella Garden at 540 mbsl. This field extends ~500 m along a scarp wall, with hydrothermal mounds extending along faults running perpendicular to the scarp, each of which has multiple smoker vents and areas of diffuse flow. There was evidence for phase separation, with a negatively buoyant fluid phase exiting some vent orifices and descending along the vent wall; and evidence for gas phase condensing after leaving some vent orifices. Gas bubble emissions were not uncommon. Isosampler sensors were available that were configured for lower temperature measurements at Gallionella Garden. While capable of detecting variations in effluent at the 4 millidegree level, the temperature ceiling for the sensor tips available aboard ship was 260 deg C (800 deg C-capable isosampler sensors will be available for the 2006 field season). At this depth the phase separation point of seawater is 263 deg C. An isosampler sensor was deployed directly atop an apparently phase-separated white smoker chimney. The sensor indicated 260 deg C before terminating measurement. This was repeated at another vent site, indicating that the fluids were venting at the point of phase separation. Indicated smoker plume flow rates were approximately 1/2 meter per second. A second field "Soria Moria" of high temperature vents was discovered. This field is ~100 m on a side, and is densely populated by active white smoker chimneys, also with evidence for phase-separated flow. These vent fields comprise the first ever arctic vent plume sources ever visited by ROV and measured directly at the source of emission. A return to this area, and exploration and measurement further north is anticipated for 2006. The planned work includes comprehensive Isosampler and bioreactor fluid flow, sampling, geochemical and biogeochemical sampling and incubation.
UR: http://www.interridge.org/sciencewriteratsea/norway2005/index.html
DE: 3015 Heat flow (benthic)
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3094 Instruments and techniques
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005