Microscale δ34S heterogeneities in cold seep barite record variable methane flux off the Lofoten-Veståralen Continental Margin, Norway

Gas hydrate provinces occur in two sedimentary basins along Brazil’s continental margin: (1) The Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocenters was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults formed by the gravitational collapse of both depocenters. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements, and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510 and 760 m in the Rio Grande Cone and between 500 and 670 m in the Amazon deep-sea fan), but also in deeper waters within the stability zone. Gas venting along the feather edge of the stability zone could reflect gas hydrate dissociation and release to the oceans, as inferred on other continental margins, or upward fluid flow through the stability zone facilitated by tectonic structures recording the gravitational collapse of both depocenters. The potential quantity of venting gas on the Brazilian margin under different scenarios of natural or anthropogenic change requires further investigation. The studied areas provide natural laboratories where these critical processes can be analyzed and quantified.

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A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

Biogeosciences Discussions ◽

10.5194/bgd-11-7853-2014 ◽

2014 ◽

Vol 11 (6) ◽

pp. 7853-7900

Author(s):

D. Archer

Keyword(s):

Continental Shelf ◽

Sea Level ◽

Continental Margin ◽

Methane Flux ◽

Soil Freezing ◽

Sediment Surface ◽

Atmospheric Methane ◽

Pore Waters ◽

Methane Cycle ◽

The Impact

Abstract. A two-dimensional model of a passive continental margin was adapted to the simulation of the methane cycle on Siberian continental shelf and slope, attempting to account for the impacts of glacial/interglacial cycles in sea level, alternately exposing the continental shelf to freezing conditions with deep permafrost formation during glacial times, and immersion in the ocean in interglacial times. The model is used to gauge the impact of the glacial cycles, and potential anthropogenic warming in the deep future, on the atmospheric methane emission flux, and the sensitivities of that flux to processes such as permafrost formation and terrestrial organic carbon (Yedoma) deposition. Hydrological forcing drives a freshening and ventilation of pore waters in areas exposed to the atmosphere, which is not quickly reversed by invasion of seawater upon submergence, since there is no analogous saltwater pump. This hydrological pump changes the salinity enough to affect the stability of permafrost and methane hydrates on the shelf. Permafrost formation inhibits bubble transport through the sediment column, by construction in the model. The impact of permafrost on the methane budget is to replace the bubble flux by offshore groundwater flow containing dissolved methane, rather than accumulating methane for catastrophic release when the permafrost seal fails during warming. By far the largest impact of the glacial/interglacial cycles on the atmospheric methane flux is attenuation by dissolution of bubbles in the ocean when sea level is high. Methane emissions are highest during the regression (soil freezing) part of the cycle, rather than during transgression (thawing). The model-predicted methane flux to the atmosphere in response to a warming climate is small, relative to the global methane production rate, because of the ongoing flooding of the continental shelf. A slight increase due to warming could be completely counteracted by sea level rise on geologic time scales, decreasing the efficiency of bubble transit through the water column. The methane cycle on the shelf responds to climate change on a long time constant of thousands of years, because hydrate is excluded thermodynamically from the permafrost zone by water limitation, leaving the hydrate stability zone at least 300 m below the sediment surface.

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Bacterial diversity and biogeochemistry of different chemosynthetic habitats of the REGAB cold seep (West African margin, 3160 m water depth)

Biogeosciences Discussions ◽

10.5194/bgd-9-8337-2012 ◽

2012 ◽

Vol 9 (7) ◽

pp. 8337-8385 ◽

Cited By ~ 5

Author(s):

P. Pop Ristova ◽

F. Wenzhöfer ◽

A. Ramette ◽

M. Zabel ◽

D. Fischer ◽

...

Keyword(s):

Bacterial Community ◽

Water Depth ◽

Bacterial Communities ◽

Interdisciplinary Approach ◽

Methane Flux ◽

West African ◽

Cold Seep ◽

Sediment Geochemistry ◽

Methane Consumption ◽

Oxidation Of Methane

Abstract. The giant pockmark REGAB (West African margin, 3160 m water depth) is an active methane-emitting cold seep ecosystem, where the energy derived from microbially mediated oxidation of methane supports high biomass and diversity of chemosynthetic communities. Bare sediments interspersed with heterogeneous chemosynthetic assemblages of mytilid mussels, vesicomyid clams and siboglinid tubeworms form a complex seep ecosystem. To better understand if benthic bacterial communities reflect the patchy distribution of chemosynthetic fauna, all major chemosynthetic habitats at REGAB were investigated using an interdisciplinary approach combining porewater geochemistry, in situ quantification of fluxes and consumption of methane, as well bacterial community fingerprinting. This study revealed that sediments populated by different fauna assemblages show distinct biogeochemical activities and are associated with distinct sediment bacterial communities. The methane consumption and methane effluxes ranged over one to two orders of magnitude across habitats, and reached highest values at the mussel habitat, which hosted a different bacterial community compared to the other habitats. Clam assemblages had a profound impact on the sediment geochemistry, but less so on the bacterial community structure. Moreover, all clam assemblages at REGAB were restricted to sediments characterized by complete methane consumption in the seafloor, and intermediate biogeochemical activity. Overall, variations in the sediment geochemistry were reflected in the distribution of both fauna and microbial communities; and were mostly determined by methane flux.

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Numerical Simulation on Authigenic Barite Formation in Marine Sediments

Minerals ◽

10.3390/min9020098 ◽

2019 ◽

Vol 9 (2) ◽

pp. 98 ◽

Cited By ~ 2

Author(s):

Tianfu Xu ◽

Songhua Shang ◽

Hailong Tian ◽

Keqi Bei ◽

Yuqing Cao

Keyword(s):

Numerical Simulation ◽

Methane Flux ◽

Simulation Method ◽

Cold Seep ◽

Anaerobic Oxidation Of Methane ◽

Forming Process ◽

Authigenic Minerals ◽

Methane Leakage ◽

Leakage Flux ◽

Oxidation Of Methane

Submarine cold seep and its associated authigenic minerals in sediment are meaningful to indicate the existence of underlying natural gas hydrate. The anaerobic oxidation of methane (AOM) is coupled with sulfate reduction (SR) and influences the dissolution and precipitation of barite. However, the forming mechanism of barite is not yet clearly understood. In order to investigate the forming process of authigenic barite and its relationship with methane leakage flux, based on the measured data of the Qiongdongnan Basin in the Northern slope of the South China Sea, we constructed a 1D model of a sedimentary column to reproduce the formation of barite using the numerical simulation method. The results show that the original equilibrium of barite was broken by the cold seep fluids and Ba2+ was carried upward to the sulfate-rich zone leading to the formation of barite front. When there is no flux of methane from the bottom of sediment, the barite front disappears. The relationship between methane leakage flux and authigenic minerals was also discussed. It can be concluded that high methane flux corresponds to a shallow barite front in the sediment, furthermore, the barite content first increases and then decreases as the methane flux increases. At the same time, an inverse relationship between the ratio of authigenic barite to calcite and methane flux was obtained.

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Atypical biological features of a new cold seep site on the Lofoten-Vesterålen continental margin (northern Norway)

Scientific Reports ◽

10.1038/s41598-018-38070-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 9

Author(s):

Arunima Sen ◽

Tobias Himmler ◽

Wei Li Hong ◽

Cheshtaa Chitkara ◽

Raymond W. Lee ◽

...

Keyword(s):

Continental Margin ◽

Cold Seep ◽

Northern Norway ◽

Biological Features ◽

Seep Site

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Bacterial diversity and biogeochemistry of different chemosynthetic habitats of the REGAB cold seep (West African margin, 3160 m water depth)

Biogeosciences ◽

10.5194/bg-9-5031-2012 ◽

2012 ◽

Vol 9 (12) ◽

pp. 5031-5048 ◽

Cited By ~ 27

Author(s):

P. Pop Ristova ◽

F. Wenzhöfer ◽

A. Ramette ◽

M. Zabel ◽

D. Fischer ◽

...

Keyword(s):

Bacterial Community ◽

Water Depth ◽

Bacterial Communities ◽

Interdisciplinary Approach ◽

Methane Flux ◽

West African ◽

Cold Seep ◽

Sediment Geochemistry ◽

Water Geochemistry ◽

Methane Consumption

Abstract. The giant pockmark REGAB (West African margin, 3160 m water depth) is an active methane-emitting cold seep ecosystem, where the energy derived from microbially mediated oxidation of methane supports high biomass and diversity of chemosynthetic communities. Bare sediments interspersed with heterogeneous chemosynthetic assemblages of mytilid mussels, vesicomyid clams and siboglinid tubeworms form a complex seep ecosystem. To better understand if benthic bacterial communities reflect the patchy distribution of chemosynthetic fauna, all major chemosynthetic habitats at REGAB were investigated using an interdisciplinary approach combining pore water geochemistry, in situ quantification of fluxes and consumption of methane, as well as bacterial community fingerprinting. This study revealed that sediments populated by different fauna assemblages show distinct biogeochemical activities and are associated with distinct sediment bacterial communities. The methane consumption rates and methane effluxes ranged over one to two orders of magnitude across habitats, and reached highest values at the mussel habitat, which hosted a different bacterial community compared to the other habitats. Clam assemblages had a profound impact on the sediment geochemistry, but less so on the bacterial community structure. Moreover, all clam assemblages at REGAB were restricted to sediments characterized by complete methane consumption in the seafloor, and intermediate biogeochemical activity. Overall, variations in the sediment geochemistry were reflected in the distribution of both fauna and microbial communities; and were mostly determined by methane flux.

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First discovery of a cold seep on the continental margin of the central Red Sea

Journal of Marine Systems ◽

10.1016/j.jmarsys.2011.12.004 ◽

2012 ◽

Vol 94 ◽

pp. 247-253 ◽

Cited By ~ 25

Author(s):

Zenon B. Batang ◽

Evangelos Papathanassiou ◽

Abdulaziz Al-Suwailem ◽

Chris Smith ◽

Maria Salomidi ◽

...

Keyword(s):

Red Sea ◽

Continental Margin ◽

Cold Seep

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Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin

10.20944/preprints201904.0063.v1 ◽

2019 ◽

Author(s):

Marcelo Ketzer ◽

Daniel Praeg ◽

Maria A.G. Pivel ◽

Adolpho H. Augustin ◽

Luiz F. Rodrigues ◽

...

Keyword(s):

Continental Margin ◽

Gas Hydrate ◽

Deep Sea ◽

Rio Grande ◽

Cold Seep ◽

Stability Zone ◽

Tectonic Structures ◽

The Stability ◽

Sea Fan ◽

Hydrate Stability

Gas hydrate provinces are present in at least in two areas along Brazil’s continental margin: (1) the Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocentres was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510-760 m in the Rio Grande Cone and 500-670 m in the Amazon deep-sea fan) but also in deeper waters within the stability zone. Gas venting along the feather edge of the stability zone could reflect gas hydrate dissociation and release to the oceans, as inferred on other continental margins, or upward fluid flow through the stability zone facilitated by tectonic structures recording the gravitational collapse of both depocentres. The potential quantity of venting gas on the Brazilian margin under different scenarios of natural or anthropogenic change require further investigation. The studied areas provide a natural laboratory where these critical processes can be analysed and quantified.

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Deeply Buried Authigenic Carbonates in the Qiongdongnan Basin, South China Sea: Implications for Ancient Cold Seep Activities

Minerals ◽

10.3390/min10121135 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1135

Author(s):

Jiangong Wei ◽

Tingting Wu ◽

Wei Zhang ◽

Yinan Deng ◽

Rui Xie ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Methane Flux ◽

Qiongdongnan Basin ◽

Cold Seep ◽

Carbonate Precipitation ◽

Methane Seep ◽

China Sea ◽

Methane Seepage ◽

Sediment Layers

Cold seep carbonates are important archives of pore water chemistry and ancient methane seepage activity. They also provide an important contribution to the global carbon sink. Seep carbonates at three sediment layers (3.0, 52.1, and 53.6 mbsf) were collected at site W08B in the Qiongdongnan Basin of the South China Sea. This study investigated the mineralogy, microstructure, stable carbon and oxygen isotopes, trace elements, and U-Th dates of these carbonates to identify the relationship between methane flux and authigenic carbonate precipitation. The results showed that the δ13C and δ18O values of all carbonates are similar, indicating that the carbon source for shallow carbonates and deep carbonates has remained constant over time and included biogenic and thermogenic methane. Although carbonates were found in three sediment layers, the two main stages of methane seepage events were discernible, which was likely caused by the dissociation of gas hydrates. The first methane seep took place at 131.1–136.3 ka BP. During a dramatic drop in the sea level, the seep carbonate at 52.1 mbsf formed at 136.3 ka BP through the anaerobic oxidation of methane (AOM). The carbonate at 53.6 mbsf resulted from the vertical downward movement of the sulfate-methane transition zone with decreasing methane flux at 131.1 ka BP. This is the reason for the age of carbonates at 52.1 mbsf being older than the age of carbonates at 53.6 mbsf. The second methane seep took place at 12.2 ka BP. Shallow carbonate formed at that time via AOM and is now located at 3 mbsf. Moreover, thin-section photomicrographs of deep carbonate mainly consisted of matrix micrite and biological debris and acicular aragonite occurred as vein cement filling the pore spaces between the matrix micrite. The acicular aragonite was mainly influenced by the timing of the carbonate precipitation of minerals. This research identified a long history of methane seep activity reflected by the vertical distribution of carbonates.

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Characterization of Carbonate Crust from a Recently Discovered Methane Seep on the North Atlantic Continental Margin of the USA

Minerals ◽

10.3390/min9030138 ◽

2019 ◽

Vol 9 (3) ◽

pp. 138

Author(s):

Rinat Gabitov ◽

Chiara Borrelli ◽

Jacob Buettner ◽

Brenda Kirkland ◽

Adam Skarke ◽

...

Keyword(s):

Mass Spectrometry ◽

Continental Margin ◽

North Atlantic ◽

Inductively Coupled Plasma ◽

Carbonate Rock ◽

Iron Sulfide ◽

Cold Seep ◽

Anaerobic Oxidation Of Methane ◽

Carbon And Oxygen Isotopes

This study is focused on mineralogical and chemical characterization of an authigenic carbonate rock (crust) collected at a recently discovered cold seep on the US North Atlantic continental margin. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the carbonate rock is composed of microcrystalline aragonite cement, white acicular aragonite crystals (AcAr), equant quartz crystals, small microcrystalline aluminosilicates, and trace amounts of iron sulfide microcrystals. Element/calcium ratios were measured with laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) using a calcite standard, which was prepared by annealing USGS certified carbonate powder (MACS-3). The occurrence of microscopic, non-carbonate inclusions precluded evaluation of trace elements in the aragonite cement, but allowed for in situ analysis of AcAr crystals. Carbon and oxygen isotopes were analyzed via isotope ratio mass spectrometry (IRMS) and expressed as δ13C and δ18O. Low δ13C values suggest that aragonite grew as a result of anaerobic oxidation of methane and observed δ18O values indicate that the temperature of aragonite crystallization was 1.7–1.9 °C.

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