The Impact of Methane Seepage on the Pore-Water Geochemistry across the East Siberian Arctic Shelf

East Siberian Arctic Shelf, the widest and the shallowest shelf of the World Ocean, covering greater than two million square kilometers, has recently been shown to be a significant modern source of atmospheric methane (CH4). The CH4 emitted to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits (pre-formed CH4 preserved as free gas and/or gas hydrates). This paper focuses primarily on understanding the source and transformation of geofluid in the methane seepage areas using ions/trace elements and element ratios in the sediment pore-water. Six piston cores and totally 42 pore-water samples were collected in the East Siberian Sea and the Laptev Sea at water depths ranging from 22 to 68 m. In the active zones of methane release, concentrations of vanadium, thorium, phosphorus, aluminum are increased, while concentrations of cobalt, iron, manganese, uranium, molybdenum, copper are generally low. The behavior of these elements is determined by biogeochemical processes occurring in the pore-waters at the methane seeps sites (sulfate reduction, anaerobic oxidation of methane, secondary precipitation of carbonates and sulfides). These processes affect the geochemical environment and, consequently, the species of these elements within the pore-waters and the processes of their redistribution in the corresponding water–rock system.

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Interaction between hydrocarbon seepage, chemosynthetic communities and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

Biogeosciences Discussions ◽

10.5194/bgd-8-9763-2011 ◽

2011 ◽

Vol 8 (5) ◽

pp. 9763-9811 ◽

Cited By ~ 5

Author(s):

D. Fischer ◽

H. Sahling ◽

K. Nöthen ◽

G. Bohrmann ◽

M. Zabel ◽

...

Keyword(s):

Hydrogen Sulfide ◽

Pore Water ◽

Bottom Water ◽

Microbial Mats ◽

Lower Boundary ◽

Accretionary Prism ◽

Anaerobic Oxidation Of Methane ◽

Cold Seeps ◽

Remotely Operated Vehicle ◽

Geochemical Environment

Abstract. The interaction between fluid seepage, bottom water redox, and chemosynthetic communities was studied at cold seeps across one of the world's largest oxygen minimum zones (OMZ) located at the Makran convergent continental margin. Push cores were obtained from seeps within and at the lower boundary of the core-OMZ with a remotely operated vehicle. Extracted pore water was analyzed for sulfide and sulfate contents. Depending on oxygen availability, seeps were either colonized by microbial mats or by mats and macrofauna. The latter, including ampharetid polychaetes and vesicomyid clams, occurred in distinct benthic habitats which were arranged in a concentric fashion around gas orifices. At most sites colonized by microbial mats, hydrogen sulfide was exported into the bottom water. Where macrofauna was widely abundant, hydrogen sulfide was consumed within the sediment. Numerical modeling of pore water profiles was performed in order to assess rates of fluid advection and bioirrigation. While the magnitude of upward fluid flow decreased from 11 cm yr−1 to <1 cm yr−1 and the sulfate/methane transition zone (SMTZ) deepened with increasing distance from the central gas orifice, the fluxes of sulfate into the SMTZ did not significantly differ (6.6–9.3 mol m−2 yr−1). Depth-integrated rates of bioirrigation increased from 162 cm yr−1 in central habitats characterized by microbial mats and sparse macrofauna to 348 cm yr−1 in habitats of large and small vesicomyid clams. These results reveal that chemosynthetic macrofauna inhabiting the outer seep habitats at the lower boundary of the OMZ efficiently bioirrigate and thus transport sulfate into the upper 10 to 15 cm of the sediment. In this way bioirrigation compensates for the lower upward flux of methane in outer habitats and stimulates rates of anaerobic oxidation of methane (AOM) with sulfate high enough to provide sulfide for chemosynthesis. Through bioirrigation macrofauna engineer their geochemical environment and fuel upward sulfide flux via AOM. Due to the introduction of oxygenated bottom water into the sediment via bioirrigation the depth of the sulfide sink gradually deepens towards outer habitats. We therefore suggest that – in addition to the oxygen levels in the water column which determine whether macrofaunal communities can develop or not – it is rather the depth of the SMTZ and thus of sulfide production that determines which chemosynthetic communities are able to exploit the sulfide at depth. Moreover, large vesicomyid clams most efficiently expand the sulfate zone in the sediment and cut off smaller or immobile organisms from the sulfide source.

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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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Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

Biogeosciences ◽

10.5194/bg-9-2013-2012 ◽

2012 ◽

Vol 9 (6) ◽

pp. 2013-2031 ◽

Cited By ~ 52

Author(s):

D. Fischer ◽

H. Sahling ◽

K. Nöthen ◽

G. Bohrmann ◽

M. Zabel ◽

...

Keyword(s):

Hydrogen Sulfide ◽

Pore Water ◽

Bottom Water ◽

Microbial Mats ◽

Accretionary Prism ◽

Anaerobic Oxidation Of Methane ◽

Cold Seeps ◽

Remotely Operated Vehicle ◽

Geochemical Environment ◽

The Core

Abstract. The interaction between fluid seepage, bottom water redox, and chemosynthetic communities was studied at cold seeps across one of the world's largest oxygen minimum zones (OMZ) located at the Makran convergent continental margin. Push cores were obtained from seeps within and below the core-OMZ with a remotely operated vehicle. Extracted sediment pore water was analyzed for sulfide and sulfate concentrations. Depending on oxygen availability in the bottom water, seeps were either colonized by microbial mats or by mats and macrofauna. The latter, including ampharetid polychaetes and vesicomyid clams, occurred in distinct benthic habitats, which were arranged in a concentric fashion around gas orifices. At most sites colonized by microbial mats, hydrogen sulfide was exported into the bottom water. Where macrofauna was widely abundant, hydrogen sulfide was retained within the sediment. Numerical modeling of pore water profiles was performed in order to assess rates of fluid advection and bioirrigation. While the magnitude of upward fluid flow decreased from 11 cm yr−1 to <1 cm yr−1 and the sulfate/methane transition (SMT) deepened with increasing distance from the central gas orifice, the fluxes of sulfate into the SMT did not significantly differ (6.6–9.3 mol m−2 yr−1). Depth-integrated rates of bioirrigation increased from 120 cm yr−1 in the central habitat, characterized by microbial mats and sparse macrofauna, to 297 cm yr−1 in the habitat of large and few small vesicomyid clams. These results reveal that chemosynthetic macrofauna inhabiting the outer seep habitats below the core-OMZ efficiently bioirrigate and thus transport sulfate down into the upper 10 to 15 cm of the sediment. In this way the animals deal with the lower upward flux of methane in outer habitats by stimulating rates of anaerobic oxidation of methane (AOM) with sulfate high enough to provide hydrogen sulfide for chemosynthesis. Through bioirrigation, macrofauna engineer their geochemical environment and fuel upward sulfide flux via AOM. Furthermore, due to the introduction of oxygenated bottom water into the sediment via bioirrigation, the depth of the sulfide sink gradually deepens towards outer habitats. We therefore suggest that – in addition to the oxygen levels in the water column, which determine whether macrofaunal communities can develop or not – it is the depth of the SMT and thus of sulfide production that determines which chemosynthetic communities are able to exploit the sulfide at depth. We hypothesize that large vesicomyid clams, by efficiently expanding the sulfate zone down into the sediment, could cut off smaller or less mobile organisms, as e.g. small clams and sulfur bacteria, from the sulfide source.

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Characteristics of Authigenic Minerals around the Sulfate-Methane Transition Zone in the Methane-Rich Sediments of the Northern South China Sea: Inorganic Geochemical Evidence

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph16132299 ◽

2019 ◽

Vol 16 (13) ◽

pp. 2299 ◽

Cited By ~ 5

Author(s):

Daidai Wu ◽

Tiantian Sun ◽

Rui Xie ◽

Mengdi Pan ◽

Xuegang Chen ◽

...

Keyword(s):

South China Sea ◽

Transition Zone ◽

South China ◽

Total Carbon ◽

Cold Seep ◽

Anaerobic Oxidation Of Methane ◽

Authigenic Minerals ◽

China Sea ◽

Methane Seepage ◽

The Impact

Sediments at marine cold seep areas provide potential archives of past fluid flow, which allow insights into the evolution of past methane seepage activities. However, signals for anaerobic oxidation of methane (AOM) might be obscured in bulk sediments in cold-seep settings due to several factors, especially flood and turbidite deposition. Comprehensive inorganic data were gathered in this study to explore the availability of related records at cold seeps and to provide insights into the evolution of past methane seepage activities. Sediments collected from the site 973-4 in the Taixinan Basin on the northern slope of the South China Sea were characterized in terms of total carbon and sulfur, δ13C values of total organic carbon (δ13CTIC), δ34S values of chromium reducible sulfur (δ34SCRS), and foraminiferal oxygen and carbon isotopes. The results confirmed a strong correlation between formation of authigenic minerals and AOM. Moreover, the 34S enrichments and abundant chromium reducible sulfur (CRS) contents in the authigenic sulfides in the sulfate–methane transition zone (SMTZ) within 619–900 cm below seafloor (cmbsf) reflected past high methane fluxes supported by constant methane seepages. Lithological distribution and AMS (Accelerator Mass Spectra) 14C dating of planktonic foraminifera show that the turbidite (~35.14 ka) was related to a foraminifera-rich interval (Unit II: 440-619 cmbsf) and increased carbonate productivity during the last glacial maximum (LGM). Enrichment of Mo and U was observed accompanied by low contents of nutrient metals (Al, Ti, V, Ni, Fe, Mn, and Cu) in Unit II. The foraminifera-rich interval (Unit II) of cold seep sediments was probably linked to the phenomenon of inconsecutive sedimentary sequence due to the turbidites, which resulted in the lack of Fe, Mn, and Ba enrichment. There is no U enrichment but only Mo enrichment within Unit III, which might be related to H2S produced by AOM during the methane seepages. Based on the above results, it can be speculated that this area has experienced multiple-episodes of methane seep events. Further exploration of AOM should focus on the risks of rapid deposition, especially the impact of turbidity current on sediments.

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Impact of sampling techniques on the concentration of ammonia and sulfide in pore water of marine sediments

Oceanological and Hydrobiological Studies ◽

10.1515/ohs-2019-0017 ◽

2019 ◽

Vol 48 (2) ◽

pp. 184-195 ◽

Cited By ~ 1

Author(s):

Aleksandra Brodecka-Goluch ◽

Patrycja Siudek ◽

Jerzy Bolałek

Keyword(s):

Pore Water ◽

Sediment Cores ◽

Ex Situ ◽

Water Sampling ◽

Air Filtration ◽

Pore Waters ◽

Atmospheric Air ◽

Water Constituents ◽

Sampling Procedures ◽

The Impact

Abstract Three ex situ pore water sampling procedures (I – rhizon samplers, II – centrifugation of sediment subsamples collected from different sediment depths without core sectioning, III – core sectioning and centrifugation of sediment sections) were compared to indicate factors that may affect concentrations of pore water constituents (ammonia and sulfides). The methods were selected and modified in such a way as to determine how the concentrations are affected by different factors related to sampling procedures, e.g. contact with atmospheric air, filtration and sediment core disturbance. They were tested on nine sediment cores collected at one site in the southern Baltic Sea. The concentration of ammonia in pore water from centrifuged sediment sections was significantly higher compared to pore water extracted by rhizons – probably due to the impact of changing pH. The factor with the greatest impact on the H2S/HS– concentration in the analyzed pore water was the contact with atmospheric air and/or the extrusion of sediments from a core liner. Rhizons proved to be the best option for sampling pore waters analyzed for H2S/HS– and NH4+/NH3. In the case of H2S/HS– we noticed the smallest loss of the analyzed constituents. For ammonia, the centrifugation of the whole sediment sections was likely to cause interferences in the indophenol blue method.

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Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf

Biogeosciences ◽

10.5194/bg-17-3247-2020 ◽

2020 ◽

Vol 17 (12) ◽

pp. 3247-3275

Author(s):

Matteo Puglini ◽

Victor Brovkin ◽

Pierre Regnier ◽

Sandra Arndt

Keyword(s):

Environmental Conditions ◽

Transport Processes ◽

Arctic Shelf ◽

Delayed Response ◽

Anaerobic Oxidation Of Methane ◽

Laptev Sea ◽

Ch4 Flux ◽

Wide Range ◽

Siberian Arctic ◽

Methane Efflux

Abstract. The East Siberian Arctic Shelf (ESAS) hosts large yet poorly quantified reservoirs of subsea permafrost and associated gas hydrates. It has been suggested that the global-warming induced thawing and dissociation of these reservoirs is currently releasing methane (CH4) to the shallow coastal ocean and ultimately the atmosphere. However, a major unknown in assessing the contribution of this CH4 flux to the global CH4 cycle and its climate feedbacks is the fate of CH4 as it migrates towards the sediment–water interface. In marine sediments, (an)aerobic oxidation reactions generally act as a very efficient methane sink. However, a number of environmental conditions can reduce the efficiency of this biofilter. Here, we used a reaction-transport model to assess the efficiency of the benthic methane filter and, thus, the potential for benthic methane escape across a wide range of environmental conditions that could be encountered on the East Siberian Arctic Shelf. Results show that, under steady-state conditions, anaerobic oxidation of methane (AOM) acts as an efficient biofilter. However, high CH4 escape is simulated for rapidly accumulating and/or active sediments and can be further enhanced by the presence of organic matter with intermediate reactivity and/or intense local transport processes, such as bioirrigation. In addition, in active settings, the sudden onset of CH4 flux triggered by, for instance, permafrost thaw or hydrate destabilization can also drive a high non-turbulent methane escape of up to 19 µmol CH4 cm−2 yr−1 during a transient, multi-decadal period. This “window of opportunity” arises due to delayed response of the resident microbial community to suddenly changing CH4 fluxes. A first-order estimate of non-turbulent, benthic methane efflux from the Laptev Sea is derived as well. We find that, under present-day conditions, non-turbulent methane efflux from Laptev Sea sediments does not exceed 1 Gg CH4 yr−1. As a consequence, we conclude that previously published estimates of ocean–atmosphere CH4 fluxes from the ESAS cannot be supported by non-turbulent, benthic methane escape.

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Bacterial oxidation of methane within seeps in the northern Laptev Sea

10.5194/egusphere-egu2020-22421 ◽

2020 ◽

Author(s):

Anna Yurchenko ◽

Elizaveta Krasnova ◽

Igor Semiletov ◽

Natal'ia Shakhova ◽

Mikhail Spasennykh

Keyword(s):

Stable Isotopes ◽

Gas Hydrates ◽

Arctic Shelf ◽

Anaerobic Oxidation Of Methane ◽

Laptev Sea ◽

Sampling Station ◽

Bacterial Oxidation ◽

Oxidation Of Methane ◽

Wide Range ◽

Siberian Arctic

Increase of methane concentration in atmosphere due to emission from Arctic shelf subsea deposits can play considerable role in climate change [1-2]. Methane seeps in East-Siberian and Laptev Seas were investigated in frames of complex research cruise &#1040;&#1052;&#1050;-78 onboard R/V &#171;Akademik Mstislav Keldysh&#187;, (September 17 - October 22, 2019).In the seep areas gas was collected to study its molecular and stable isotopes composition and reveal the genesis of discharging methane. Sediments were collected using box-corer for detailed lithological investigations and characterization of mineral inclusions. At the sampling station within methane seep in the Northern Laptev Sea, dark grey to black clays with hydrotroilite were collected. &#160;They contained rounded inclusions of light grey carbonates with size up to 3x4cm.Methane that migrates to the seafloor surface is characterized by wide range of stable isotopes composition values with predominance of 13C depleted biogenic component [3-4].Stable carbon and oxygen isotopes composition of carbonate inclusions was measured. The carbonates are strongly depleted in 13C up to -32,4 &#8240;VPDB. &#948;18&#1054; varies in wide range between -3 and +4,4 &#8240;VPDB. Depletion of the carbonates in 13C indicates its formation as a result of bacterial oxidation of methane in anaerobic conditions. Anaerobic oxidation of methane is an important biogeochemical process in the areas of methane emissions. The size and isotopes data of the authigenic methane-derived carbonates provide information on the intensity and time of methane discharge, geochemical characteristics of the fluids, including water. Enrichment of the carbonate inclusions in 18O can be explained by the migration of isotopically heavy water from dissociating gas hydrates [5].Obtained results of the complex study of discharging fluids and authigenic minerals allow to characterize the biochemogenic processes in seep sediments, local variations in the environmental conditions and methane flux and isotopic effects during bacterial oxidation of methane.&#160;Literature:<ol><li>Shakhova N., Semiletov I., Chuvilin E. Understanding the permafrost-hydrate system and associated methane releases in the East Siberian Arctic Shelf // Geosciences, 2019, 9, 251.</li> <li>Shakhova N.E., Sergienko V.I., Semiletov I.P. Contribution of East-Siberian shelf to the modern methane cycle // RAS bulletin, 2009, vol. 79, &#8470;6, pp. 507-518.</li> <li>Whiticar, M.J. Correlation of natural gases with their sources. In: Magoon, L., Dow, W. Eds., The Petroleum System &#8212; From Source to Trap. AAPG Memoir 60, 1994, pp. 261&#8211;284.</li> <li>Sapart, C. J., Shakhova, N., Semiletov, I., Jansen, J., Szidat, S., Kosmach, D., Dudarev, O., van der Veen, C., Egger, M., Sergienko, V.,; Salyuk, A., Tumskoy, V., Tison, J.L., Rockmann, T. The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis // Biogeosciences, 14, 9, 2283-2292, 2017.</li> <li>Bohrman G., Suess E., Greinert J., Teichert B., Naehr T. Has hydrate carbonates from Hydrate ridge, Cascadia convergent margin: indicators of near-seafloor clathrate deposits // Fourth Int. Conf. Gas Hydrates: Yokohama, Japan, 19023:102-107. 2002.</li> </ol>

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Hydrochemistry of sediment pore water in the Bratsk reservoir (Baikal region, Russia)

Scientific Reports ◽

10.1038/s41598-021-90603-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

V. I. Poletaeva ◽

E. N. Tirskikh ◽

M. V. Pastukhov

Keyword(s):

Pore Water ◽

Ionic Composition ◽

Water System ◽

Water Reservoir ◽

Environmental Parameters ◽

Water Area ◽

Pore Waters ◽

Overlying Water ◽

Major Ion ◽

Bratsk Reservoir

AbstractThis study aimed to identify the factors responsible for the major ion composition of pore water from the bottom sediments of the Bratsk water reservoir, which is part of the largest freshwater Baikal-Angara water system. In the Bratsk reservoir, the overlying water was characterized as HCO3–Ca–Mg type with the mineralization ranging between 101.2 and 127.7 mg L−1 and pore water was characterized as HCO3–SO4–Ca, SO4–Cl–Ca–Mg and mixed water types, which had mineralization varying from 165.9 to 4608.1 mg L−1. The ionic composition of pore waters varied both along the sediment depth profile and across the water area. In pore water, the difference between the highest and lowest values was remarkably large: 5.1 times for K+, 13 times for Mg2+, 16 times for HCO3−, 20 times for Ca2+, 23 times for Na+, 80 times for SO42−, 105 times for Cl−. Such variability at different sites of the reservoir was due to the interrelation between major ion concentrations in the pore water and environmental parameters. The major factor responsible for pore water chemistry was the dissolution of sediment-forming material coming from various geochemical provinces. In the south part of the reservoir, Cl−, Na+ and SO42− concentrations may significantly increase in pore water due to the effect of subaqueous flow of highly mineralized groundwater.

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Springtime Upwelling and Its Formation Mechanism in Coastal Waters of Manaung Island, Myanmar

Remote Sensing ◽

10.3390/rs12223777 ◽

2020 ◽

Vol 12 (22) ◽

pp. 3777

Author(s):

Yuhui Li ◽

Yun Qiu ◽

Jianyu Hu ◽

Cherry Aung ◽

Xinyu Lin ◽

...

Keyword(s):

Surface Layer ◽

Satellite Remote Sensing ◽

Subsurface Layer ◽

World Ocean ◽

Remote Sensing Data ◽

Remote Forcing ◽

Forcing Mechanisms ◽

World Ocean Atlas ◽

The Impact ◽

Local Wind Forcing

Multisource satellite remote sensing data and the World Ocean Atlas 2018 (WOA18) temperature and salinity dataset have been used to analyze the spatial distribution, variability and possible forcing mechanisms of the upwelling off Manaung Island, Myanmar. Signals of upwelling exist off the coasts of Manaung Island, in western Myanmar during spring. It appears in February, reaches its peak in March and decays in May. Low-temperature (<28.3 °C) and high-salinity (>31.8 psu) water at the surface of this upwelling zone is caused by the upwelling of seawater from a depth below 100 m. The impact of the upwelling on temperature is more significant in the subsurface layer than that in the surface layer. In contrast, the impact of the upwelling on salinity in the surface layer is more significant. Further research reveals that the remote forcing from the equator predominantly induces the evolution of the upwelling, while the local wind forcing also contributes to strengthen the intensity of the upwelling during spring.

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