Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998
A massive release of methane on the Cascadia Hydrate Ridge was documented during a ROPOS program in August 1998, consistent with previously reported observations in 1996. An extensive survey of the seafloor revealed that the seeps lie within a narrow band trending 109 degrees. This feature parallels...
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[Corvallis, Or.] : College of Oceanic & Atmospheric Sciences, Oregon State University
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ftoregonstate:ir.library.oregonstate.edu:rx913r542 2024-04-21T08:06:59+00:00 Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 Torres, Marta E. Brown, Kevin Collier, Robert W. deAngelis, Marie Hammond, Douglas McManus, James Rehder, Gregor Trehu, Anne College of Oceanic and Atmospheric Sciences 6876680 bytes application/pdf https://ir.library.oregonstate.edu/concern/defaults/rx913r542 English [eng] eng unknown [Corvallis, Or.] : College of Oceanic & Atmospheric Sciences, Oregon State University https://ir.library.oregonstate.edu/concern/defaults/rx913r542 Copyright Not Evaluated Natural gas -- Hydrate Ridge -- Hydrates Marine sediments -- Hydrate Ridge Geochemistry -- Hydrate Ridge Technical Report ftoregonstate 2024-03-28T02:03:08Z A massive release of methane on the Cascadia Hydrate Ridge was documented during a ROPOS program in August 1998, consistent with previously reported observations in 1996. An extensive survey of the seafloor revealed that the seeps lie within a narrow band trending 109 degrees. This feature parallels larger mounds imaged by Seabeam as well as larger structures of the accretionary prism such as the Daisy bank. The area of intense bubbling is characterized by extensive bacterial mats. Large clam fields were observed ten's of meters away from the gas seeps. A third province with carbonate blocks but no clams or bacterial mats was mapped approximately 200 meters away from the seeps. To constrain fluid flow through the sediments, we deployed 8 osomotic flow meters. The areas of gas discharge are discrete and highly focussed within conduits with an approximate cross-sectional area of 5 cm2. We estimate the gas flow rate to be on the order of 5 liters/minute. While the subsurface plumbing is unknown, the high flow rate of the sampled gas seep suggests a very short transit time from the gas source (presumably the base of the BSR at 70 mbsf) to the sea floor. The Rn/CH4 ratio in gas samples collected from the gas vents is very high, approximately 50 dpm/liter (stp) CH4. Using these values, we estimate that the time required for the fluids to transit 70 m is approximately 1 hour. To further constrain the nature of the discharging fluids, we will analyze samples for their elemental and isotopic composition. Methane hydrate should be stable at the temperature and pressure conditions at the seafloor on Hydrate Ridge. Indeed, solid hydrate was observed to form within the gas samplers as well as on the camera itself, supporting the conclusion that methane is rapidly transported to the seafloor from beneath the BSR within discrete conduits, most likely separated from significant amounts of pore water. When discharged at the seafloor, some of the methane precipitate as hydrate and some continues to rise within the water column. ... Report Methane hydrate ScholarsArchive@OSU (Oregon State University) |
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Open Polar |
collection |
ScholarsArchive@OSU (Oregon State University) |
op_collection_id |
ftoregonstate |
language |
English unknown |
topic |
Natural gas -- Hydrate Ridge -- Hydrates Marine sediments -- Hydrate Ridge Geochemistry -- Hydrate Ridge |
spellingShingle |
Natural gas -- Hydrate Ridge -- Hydrates Marine sediments -- Hydrate Ridge Geochemistry -- Hydrate Ridge Torres, Marta E. Brown, Kevin Collier, Robert W. deAngelis, Marie Hammond, Douglas McManus, James Rehder, Gregor Trehu, Anne Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 |
topic_facet |
Natural gas -- Hydrate Ridge -- Hydrates Marine sediments -- Hydrate Ridge Geochemistry -- Hydrate Ridge |
description |
A massive release of methane on the Cascadia Hydrate Ridge was documented during a ROPOS program in August 1998, consistent with previously reported observations in 1996. An extensive survey of the seafloor revealed that the seeps lie within a narrow band trending 109 degrees. This feature parallels larger mounds imaged by Seabeam as well as larger structures of the accretionary prism such as the Daisy bank. The area of intense bubbling is characterized by extensive bacterial mats. Large clam fields were observed ten's of meters away from the gas seeps. A third province with carbonate blocks but no clams or bacterial mats was mapped approximately 200 meters away from the seeps. To constrain fluid flow through the sediments, we deployed 8 osomotic flow meters. The areas of gas discharge are discrete and highly focussed within conduits with an approximate cross-sectional area of 5 cm2. We estimate the gas flow rate to be on the order of 5 liters/minute. While the subsurface plumbing is unknown, the high flow rate of the sampled gas seep suggests a very short transit time from the gas source (presumably the base of the BSR at 70 mbsf) to the sea floor. The Rn/CH4 ratio in gas samples collected from the gas vents is very high, approximately 50 dpm/liter (stp) CH4. Using these values, we estimate that the time required for the fluids to transit 70 m is approximately 1 hour. To further constrain the nature of the discharging fluids, we will analyze samples for their elemental and isotopic composition. Methane hydrate should be stable at the temperature and pressure conditions at the seafloor on Hydrate Ridge. Indeed, solid hydrate was observed to form within the gas samplers as well as on the camera itself, supporting the conclusion that methane is rapidly transported to the seafloor from beneath the BSR within discrete conduits, most likely separated from significant amounts of pore water. When discharged at the seafloor, some of the methane precipitate as hydrate and some continues to rise within the water column. ... |
author2 |
College of Oceanic and Atmospheric Sciences |
format |
Report |
author |
Torres, Marta E. Brown, Kevin Collier, Robert W. deAngelis, Marie Hammond, Douglas McManus, James Rehder, Gregor Trehu, Anne |
author_facet |
Torres, Marta E. Brown, Kevin Collier, Robert W. deAngelis, Marie Hammond, Douglas McManus, James Rehder, Gregor Trehu, Anne |
author_sort |
Torres, Marta E. |
title |
Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 |
title_short |
Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 |
title_full |
Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 |
title_fullStr |
Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 |
title_full_unstemmed |
Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V BROWN-ROPOS cruise : August 1998 |
title_sort |
geochemical observations on hydrate ridge, cascadia margin during r/v brown-ropos cruise : august 1998 |
publisher |
[Corvallis, Or.] : College of Oceanic & Atmospheric Sciences, Oregon State University |
url |
https://ir.library.oregonstate.edu/concern/defaults/rx913r542 |
genre |
Methane hydrate |
genre_facet |
Methane hydrate |
op_relation |
https://ir.library.oregonstate.edu/concern/defaults/rx913r542 |
op_rights |
Copyright Not Evaluated |
_version_ |
1796946502940098560 |