Methane sources, distributions, and fluxes from cold vent sites at Hydrate Ridge, Cascadia Margin

Heeschen, Katja; Collier, Robert W.; Angelis, Marie A. de; Suess, Erwin; Rehder, Gregor; Линке, Петер; Klinkhammer, Gary P.

doi:10.1029/2004gb002266

Cited by 83 publications

(84 citation statements)

References 101 publications

(133 reference statements)

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“…Both clam and bacterial sites are covered with dense microbial communities that consume methane, and thus the methane released into the water is reduced significantly [19]. At the southern summit of Hydrate Ridge, the consumption rate of methane by microbial processes near the seafloor could be as high as 0.6±0.6 kg m 2 yr 1 [37], which is similar to the average methane flux out of the southern summit of Hydrate Ridge ( g o q =1.9 kg m 2 yr 1 ) [28]. Hence, the methane gas flux at bacterial mat and clam sites are both set to g o q =1.9 kg m 2 yr 1 [28].…”

Section: Numerical Modelsupporting

confidence: 54%

“…At the southern summit of Hydrate Ridge, the consumption rate of methane by microbial processes near the seafloor could be as high as 0.6±0.6 kg m 2 yr 1 [37], which is similar to the average methane flux out of the southern summit of Hydrate Ridge ( g o q =1.9 kg m 2 yr 1 ) [28]. Hence, the methane gas flux at bacterial mat and clam sites are both set to g o q =1.9 kg m 2 yr 1 [28]. At the gas discharge sites, the pore water flux is set to w o q =10 10 kg m 2 yr 1 and the methane flux is assumed to be g o q =5800 kg m 2 yr 1 .…”

Section: Numerical Modelmentioning

confidence: 51%

“…Owing to the "kinetic effect" of gas hydrate formation at the cold vent sites [7] and the sufficient supply of methane, as evidenced by the seepage of methane gas at the seafloor [27,28], the larger sediment porosity results in more reactant participating in the crystallization of gas hydrate, and therefore results in a higher gas hydrate formation rate. Hence, in this study, based on the hydrate formation rate developed by Chen and Cathles [31], we further consider the effects of pore volume changes ((1S h )) on gas hydrate formation rate.…”

Section: Numerical Modelmentioning

confidence: 99%

“…The seismic profile blanking zone below the Pinnacle indicates the pathway (arrowhead) of fluid migration from Horizon A. The fluid undergoes lateral migration owing to low permeability carbonate rocks, and vents at the southern summit of the Hydrate Ridge [24][25][26][27][28][29][30].…”

Section: Geological Setting At Southern Hydrate Ridgementioning

confidence: 99%

“…The water depth is ~800 m at the southern summit, and gas hydrate, authigenic carbonates and cold seep communities have been discovered there [11]. Vigorous streams of gas bubbles have been observed emanating from the seafloor, and the average gas flux from southern Hydrate Ridge is estimated to be ~1.9 kg m 2 yr 1 [11,27,28]. Based on the measured water flux and the occurrence of benthic communities in this area, Torres et al [19] identified three distinct active fluid provinces: the gas discharge sites, bacterial mat sites, and clam sites (Figure 1(a), 2).…”

Section: Geological Setting At Southern Hydrate Ridgementioning

confidence: 99%

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Influence of water flow on gas hydrate accumulation at cold vents

Cao

Zheng

Chen

2013

Sci. China Earth Sci.

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A cold vent is an area where methane-rich fluid seepage occurs. This seepage may alter the local temperature, salinity, and subsequent accumulation of the gas hydrate. Using a kinetic gas hydrate formation model and in situ measurement of temperature, salinity and fluid flux at the southern summit of Hydrate Ridge, we simulate the gas hydrate accumulation at three distinct fluid sites: clam, bacterial mat, and gas discharge sites. At the clam sites (pore water flux < 20 kg m 2 yr 1 ), pore water advection has little influence on temperature and salinity. However, the salinity and temperature are increased (peak salinity > 0.8 mol kg 1 ) by the formation of gas hydrate causing the base of the hydrate stability zone to move gradually from ~115 to ~70 meters below seafloor (mbsf). The gas hydrate saturation at the clam sites is relatively high. The water flux at the bacterial mat sites ranges from 100 to 2500 kg m 2 yr 1 . The water flow suppresses the increase in salinity resulting in a salinity close to or slightly higher than that of seawater (< 0.65 mol kg 1 ). Heat advection by water flow increases temperature significantly, shifting the base of the hydrate stability zone to above 50 or even 3 mbsf. The gas hydrate saturation is relatively low at the bacterial mat site. At the gas discharge sites, the pore water flux could reach 10 10 kg m 2 yr 1 , and the temperature could reach that of the source area in 9 min. There is no gas hydrate formation at the gas discharge sites. Our simulative analysis therefore reveals that a lower pore water flux would result in lower salinity, higher temperature, and a shallower base of the hydrate stability zone. This in turn induces a lower gas hydrate formation rate, lower hydrate saturation, and eventually less gas hydrate resources.cold vent, fluid seepage, temperature, salinity, gas hydrate, numerical simulation Citation:

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Section: Numerical Modelsupporting

confidence: 54%

Section: Numerical Modelmentioning

confidence: 51%

Section: Numerical Modelmentioning

confidence: 99%

Section: Geological Setting At Southern Hydrate Ridgementioning

confidence: 99%

Section: Geological Setting At Southern Hydrate Ridgementioning

confidence: 99%

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Influence of water flow on gas hydrate accumulation at cold vents

Cao

Zheng

Chen

2013

Sci. China Earth Sci.

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Analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope

Johnson

Miller

Salmi

et al. 2015

Geochem Geophys Geosyst

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Cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity. A portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the Vancouver Island and Oregon portions of the Cascadia margin. Multichannel seismic reflection profiles on the Cascadia margin show the widespread presence of Bottom Simulating Reflectors (BSRs) within the sediment column, indicating the gas hydrate reservoir extends from the deformation front at 3000 m depth to the upper limit of gas hydrate stability near 500 m water depth. In this study, we compile an inventory of methane bubble plume sites on the Cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen. High plume density anomalies are associated with both the continental shelf (<180 m) and the depth of the upper limit of methane hydrate stability depth (MHSD) that occurs near 500 m in the NE Pacific. The observed anomalies on the Cascadia slope may be due to the warming of seawater at intermediate depths, suggesting that modern climate change has begun to destabilize the climate-sensitive hydrate reservoir within the Cascadia margin sediments. Reanalysis of similar plume images on the North American Atlantic slope suggests a lack of correlation between observed plume depths and the MHSD for much of the latitudinal range.

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Time‐series measurements of bubble plume variability and water column methane distribution above Southern Hydrate Ridge, Oregon

Philip

Denny

Solomon

et al. 2016

Geochem Geophys Geosyst

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An estimated 500–2500 gigatons of methane carbon is sequestered in gas hydrate at continental margins and some of these deposits are associated with overlying methane seeps. To constrain the impact that seeps have on methane concentrations in overlying ocean waters and to characterize the bubble plumes that transport methane vertically into the ocean, water samples and time‐series acoustic images were collected above Southern Hydrate Ridge (SHR), a well‐studied hydrate‐bearing seep site ∼90 km west of Newport, Oregon. These data were coregistered with robotic vehicle observations to determine the origin of the seeps, the plume rise heights above the seafloor, and the temporal variability in bubble emissions. Results show that the locations of seep activity and bubble release remained unchanged over the 3 year time‐series investigation, however, the magnitude of gas release was highly variable on hourly time scales. Bubble plumes were detected to depths of 320–620 m below sea level (mbsl), in several cases exceeding the upper limit of hydrate stability by ∼190 m. For the first time, sustained gas release was imaged at the Pinnacle site and in‐between the Pinnacle and the Summit area of venting, indicating that the subseafloor transport of fluid and gas is not restricted to the Summit at SHR, requiring a revision of fluid‐flow models. Dissolved methane concentrations above background levels from 100 to 300 mbsl are consistent with long‐term seep gas transport into the upper water column, which may lead to the build‐up of seep‐derived carbon in regional subsurface waters and to increases in associated biological activity.

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Methane sources, distributions, and fluxes from cold vent sites at Hydrate Ridge, Cascadia Margin

Cited by 83 publications

References 101 publications

Influence of water flow on gas hydrate accumulation at cold vents

Influence of water flow on gas hydrate accumulation at cold vents

Analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope

Time‐series measurements of bubble plume variability and water column methane distribution above Southern Hydrate Ridge, Oregon

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