scholarly journals 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

2012 ◽  
Vol 9 (6) ◽  
pp. 2013-2031 ◽  
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.

scholarly journals 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

2011 ◽  
Vol 8 (5) ◽  
pp. 9763-9811 ◽  
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.

scholarly journals Mats of psychrophilic thiotrophic bacteria associated with cold seeps of the Barents Sea

2012 ◽  
Vol 9 (8) ◽  
pp. 2947-2960 ◽  
Author(s):  
S. Grünke ◽  
A. Lichtschlag ◽  
D. de Beer ◽  
J. Felden ◽  
V. Salman ◽  
...  
Keyword(s):  
Microbial Mats ◽  
Barents Sea ◽  
Freezing Point ◽  
Intergenic Spacer ◽  
16S Rrna Gene Sequencing ◽  
Visual Observation ◽  
Rrna Gene ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Oxidation Of Methane

Abstract. This study investigated the bacterial diversity associated with microbial mats of polar deep-sea cold seeps. The mats were associated with high upward fluxes of sulfide produced by anaerobic oxidation of methane, and grew at temperatures close to the freezing point of seawater. They ranged from small patches of 0.2–5 m in diameter (gray mats) to extensive fields covering up to 850 m2 of seafloor (white mats) and were formed by diverse sulfide-oxidizing bacteria differing in color and size. Overall, both the dominant mat-forming thiotrophs as well as the associated bacterial communities inhabiting the mats differed in composition for each mat type as determined by microscopy, 16S rRNA gene sequencing and automated ribosomal intergenic spacer analysis. While the smaller gray mats were associated with a highly diverse composition of sulfide oxidizers, the larger white mats were composed of only 1–2 types of gliding Beggiatoa filaments. Molecular analyses showed that most of the dominant mat-forming sulfide oxidizers were phylogenetically different from, but still closely related to, thiotrophs known from warmer ocean realms. The psychrophilic nature of the polar mat-forming thiotrophs was tested by visual observation of active mats at in situ temperature compared to their warming to >4 °C. The temperature range of mat habitats and the variation of sulfide and oxygen fluxes appear to be the main factors supporting the diversity of mat-forming thiotrophs in cold seeps at continental margins.

scholarly journals Archaeal Populations in Hypersaline Sediments Underlying Orange Microbial Mats in the Napoli Mud Volcano

2011 ◽  
Vol 77 (9) ◽  
pp. 3120-3131 ◽  
Author(s):  
Cassandre Sara Lazar ◽  
Stéphane L'Haridon ◽  
Patricia Pignet ◽  
Laurent Toffin
Keyword(s):  
Microbial Mats ◽  
Archaeal Community ◽  
Community Diversity ◽  
Mud Volcano ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Content Type ◽  
Methane Cycling ◽  
Oxidation Of Methane ◽  
Sediment Layers

ABSTRACTMicrobial mats in marine cold seeps are known to be associated with ascending sulfide- and methane-rich fluids. Hence, they could be visible indicators of anaerobic oxidation of methane (AOM) and methane cycling processes in underlying sediments. The Napoli mud volcano is situated in the Olimpi Area that lies on saline deposits; from there, brine fluids migrate upward to the seafloor. Sediments associated with a brine pool and microbial orange mats of the Napoli mud volcano were recovered during the Medeco cruise. Based on analysis of RNA-derived sequences, the “active” archaeal community was composed of many uncultured lineages, such as rice cluster V or marine benthic group D. Function methyl coenzyme M reductase (mcrA) genes were affiliated with the anaerobic methanotrophicArchaea(ANME) of the ANME-1, ANME-2a, and ANME-2c groups, suggesting that AOM occurred in these sediment layers. Enrichment cultures showed the presence of viable marine methylotrophicMethanococcoidesin shallow sediment layers. Thus, the archaeal community diversity seems to show that active methane cycling took place in the hypersaline microbial mat-associated sediments of the Napoli mud volcano.

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

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 397
Author(s):  
Natalia Guseva ◽  
Yulia Moiseeva ◽  
Darya Purgina ◽  
Elena Gershelis ◽  
Evgeniy Yakushev ◽  
...  
Keyword(s):  
Pore Water ◽  
World Ocean ◽  
Arctic Shelf ◽  
Anaerobic Oxidation Of Methane ◽  
Atmospheric Methane ◽  
Pore Waters ◽  
Geochemical Environment ◽  
Methane Seepage ◽  
Siberian Arctic ◽  
The Impact

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.

scholarly journals Mats of psychrophilic thiotrophic bacteria associated with cold seeps of the Barents Sea

2012 ◽  
Vol 9 (3) ◽  
pp. 3917-3948 ◽  
Author(s):  
S. Grünke ◽  
A. Lichtschlag ◽  
D. de Beer ◽  
J. Felden ◽  
V. Salman ◽  
...  
Keyword(s):  
Microbial Mats ◽  
Barents Sea ◽  
Freezing Point ◽  
Intergenic Spacer ◽  
16S Rrna Gene Sequencing ◽  
Visual Observation ◽  
Rrna Gene ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Large White

Abstract. This study investigated the bacterial diversity associated with microbial mats of polar deep-sea cold seeps. The mats are associated with high upward fluxes of sulfide produced by anaerobic oxidation of methane, and grow at temperatures close to the freezing point of seawater. They ranged from small patches of 0.2–5 m in diameter (gray mats) to extensive fields covering up to 850 m2 of seafloor (white mats) and were formed by diverse sulfide-oxidizing bacteria differing in color and size. Overall, both the dominant mat-forming thiotrophs as well as the associated bacterial communities inhabiting the mats differed in composition for each mat type as determined by microscopy, 16S rRNA gene sequencing and Automated Ribosomal Intergenic Spacer Analysis. While the smaller gray mats were associated with a highly diverse composition of sulfide oxidizers, the large white mats were composed of only 1–2 types of gliding Beggiatoa filaments. Molecular analyses showed that most of the dominant mat-forming sulfide oxidizers were phylogenetically different from, but still closely related to thiotrophs known from warmer ocean realms. The psychrophilic nature of the polar mat-forming thiotrophs was tested by visual observation of active mats at in situ temperature compared to their warming to >4 °C. The temperature range of mat habitats and the variation of sulfide and oxygen fluxes appear to be the main factors supporting the diversity of mat-forming thiotrophs in cold seeps at continental margins.

scholarly journals A Quantitative Assessment of Methane-Derived Carbon Cycling at the Cold Seeps in the Northwestern South China Sea

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 256 ◽  
Author(s):  
Junxi Feng ◽  
Niu Li ◽  
Min Luo ◽  
Jinqiang Liang ◽  
Shengxiong Yang ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Bottom Water ◽  
Cold Seep ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Dissolved Carbon ◽  
China Sea ◽  
Seafloor Observation ◽  
Gas Hydrate Formation

Widespread cold seeps along continental margins are significant sources of dissolved carbon to the ocean water. However, little is known about the methane turnovers and possible impact of seepage on the bottom seawater at the cold seeps in the South China Sea (SCS). We present seafloor observation and porewater data of six push cores, one piston core and three boreholes as well as fifteen bottom-water samples collected from four cold seep areas in the northwestern SCS. The depths of the sulfate–methane transition zone (SMTZ) are generally shallow, ranging from ~7 to <0.5 mbsf (meters below seafloor). Reaction-transport modelling results show that methane dynamics were highly variable due to the transport and dissolution of ascending gas. Dissolved methane is predominantly consumed by anaerobic oxidation of methane (AOM) at the SMTZ and trapped by gas hydrate formation below it, with depth-integrated AOM rates ranging from 59.0 and 591 mmol m−2 yr−1. The δ13C and Δ14C values of bottom-water dissolved inorganic carbon (DIC) suggest discharge of 13C- and 14C-depleted fossil carbon to the bottom water at the cold seep areas. Based on a two-endmember estimate, cold seeps fluids likely contribute 16–26% of the bottom seawater DIC and may have an impact on the long-term deep-sea carbon cycle. Our results reveal the methane-related carbon inventories are highly heterogeneous in the cold seep systems, which are probably dependent on the distances of the sampling sites to the seepage center. To our knowledge, this is the first quantitative study on the contribution of cold seep fluids to the bottom-water carbon reservoir of the SCS, and might help to understand the dynamics and the environmental impact of hydrocarbon seep in the SCS.

scholarly journals Distribution of Megabenthic Communities Under Contrasting Settings in Deep-Sea Cold Seeps Near Northwest Atlantic Canyons

2021 ◽  
Vol 8 ◽  
Author(s):  
Jason Cleland ◽  
Georgios Kazanidis ◽  
J. Murray Roberts ◽  
Steve W. Ross
Keyword(s):  
Deep Sea ◽  
Habitat Complexity ◽  
Microbial Mats ◽  
Oil And Gas ◽  
Human Impacts ◽  
Cold Seep ◽  
Cold Seeps ◽  
Remotely Operated Vehicle ◽  
Northwest Atlantic ◽  
Spatial Management

Cold seeps support fragile deep-sea communities of high biodiversity and are often found in areas with high commercial interest. Protecting them from encroaching human impacts (bottom trawling, oil and gas exploitation, climate change) requires an advanced understanding of the drivers shaping their spatial distribution and biodiversity. Based on the analysis of 2,075 high-quality images from six remotely operated vehicle dives, we examined cold seep megabenthic community composition, richness, density, and biodiversity at a relatively shallow (∼400 m water depth) site near Baltimore Canyon (BC) and a much deeper site (∼1,500 m) near Norfolk Canyon (NC), in the northwest Atlantic. We found sharp differences in the megabenthic composition between the sites, which were driven mostly by bathymetric gradients. At both BC and NC there were significant differences in megabenthic composition across habitats. Hard habitats in and around cold seeps had significantly higher values of species richness, density, and biodiversity than soft habitats. Depth and habitat complexity were the leading environmental variables driving megabenthic variability. The presence of microbial mats and gas bubbling sites had a statistically significant contribution to explaining megabenthic variability mainly in the shallower BC and less in the deeper NC areas examined; drivers behind this discrepancy could be related to differences between BC and NC in terms of chemical compound fluxes and megafaunal life history characteristics. Our surveys revealed marine litter, primarily from commercial fisheries. This study highlights the importance of habitat complexity for the proliferation of highly diverse cold-seep ecosystems and underscores the importance of discovery science to inform spatial management of human activities in the deep and open ocean.

scholarly journals Biogeochemistry and Community Composition of Iron- and Sulfur-Precipitating Microbial Mats at the Chefren Mud Volcano (Nile Deep Sea Fan, Eastern Mediterranean)

2008 ◽  
Vol 74 (10) ◽  
pp. 3198-3215 ◽  
Author(s):  
Enoma O. Omoregie ◽  
Vincent Mastalerz ◽  
Gert de Lange ◽  
Kristina L. Straub ◽  
Andreas Kappler ◽  
...  
Keyword(s):  
16S Rrna ◽  
16S Rrna Gene ◽  
Microbial Mats ◽  
Eastern Mediterranean ◽  
Sulfide Oxidation ◽  
Mud Volcano ◽  
Rrna Gene ◽  
Anaerobic Oxidation Of Methane ◽  
Gene Sequences ◽  
16S Rrna Gene Sequences

ABSTRACT In this study we determined the composition and biogeochemistry of novel, brightly colored, white and orange microbial mats at the surface of a brine seep at the outer rim of the Chefren mud volcano. These mats were interspersed with one another, but their underlying sediment biogeochemistries differed considerably. Microscopy revealed that the white mats were granules composed of elemental S filaments, similar to those produced by the sulfide-oxidizing epsilonproteobacterium “Candidatus Arcobacter sulfidicus.” Fluorescence in situ hybridization indicated that microorganisms targeted by a “Ca. Arcobacter sulfidicus”-specific oligonucleotide probe constituted up to 24% of the total the cells within these mats. Several 16S rRNA gene sequences from organisms closely related to “Ca. Arcobacter sulfidicus” were identified. In contrast, the orange mat consisted mostly of bright orange flakes composed of empty Fe(III) (hydr)oxide-coated microbial sheaths, similar to those produced by the neutrophilic Fe(II)-oxidizing betaproteobacterium Leptothrix ochracea. None of the 16S rRNA gene sequences obtained from these samples were closely related to sequences of known neutrophilic aerobic Fe(II)-oxidizing bacteria. The sediments below both types of mats showed relatively high sulfate reduction rates (300 nmol·cm−3·day−1) partially fueled by the anaerobic oxidation of methane (10 to 20 nmol·cm−3·day−1). Free sulfide produced below the white mat was depleted by sulfide oxidation within the mat itself. Below the orange mat free Fe(II) reached the surface layer and was depleted in part by microbial Fe(II) oxidation. Both mats and the sediments underneath them hosted very diverse microbial communities and contained mineral precipitates, most likely due to differences in fluid flow patterns.

scholarly journals Why Orange Guaymas Basin Beggiatoa spp. Are Orange: Single-Filament-Genome-Enabled Identification of an Abundant Octaheme Cytochrome with Hydroxylamine Oxidase, Hydrazine Oxidase, and Nitrite Reductase Activities

2012 ◽  
Vol 79 (4) ◽  
pp. 1183-1190 ◽  
Author(s):  
Barbara J. MacGregor ◽  
Jennifer F. Biddle ◽  
Jason R. Siebert ◽  
Eric Staunton ◽  
Eric L. Hegg ◽  
...  
Keyword(s):  
Nitrite Reductase ◽  
Pure Culture ◽  
Gulf Of California ◽  
Microbial Mats ◽  
Physiological Role ◽  
Nitrite Reduction ◽  
Cold Seeps ◽  
Single Filament ◽  
Guaymas Basin ◽  
Content Type

ABSTRACTOrange, white, and yellow vacuolatedBeggiatoaceaefilaments are visually dominant members of microbial mats found near sea floor hydrothermal vents and cold seeps, with orange filaments typically concentrated toward the mat centers. No marine vacuolateBeggiatoaceaeare yet in pure culture, but evidence to date suggests they are nitrate-reducing, sulfide-oxidizing bacteria. The nearly complete genome sequence of a single orangeBeggiatoa(“CandidatusMaribeggiatoa”) filament from a microbial mat sample collected in 2008 at a hydrothermal site in Guaymas Basin (Gulf of California, Mexico) was recently obtained. From this sequence, the gene encoding an abundant soluble orange-pigmented protein in Guaymas Basin mat samples (collected in 2009) was identified by microcapillary reverse-phase high-performance liquid chromatography (HPLC) nano-electrospray tandem mass spectrometry (μLC–MS-MS) of a pigmented band excised from a denaturing polyacrylamide gel. The predicted protein sequence is related to a large group of octaheme cytochromes whose few characterized representatives are hydroxylamine or hydrazine oxidases. The protein was partially purified and shown byin vitroassays to have hydroxylamine oxidase, hydrazine oxidase, and nitrite reductase activities. From what is known ofBeggiatoaceaephysiology, nitrite reduction is the most likelyin vivorole of the octaheme protein, but future experiments are required to confirm this tentative conclusion. Thus, while present-day genomic and proteomic techniques have allowed precise identification of an abundant mat protein, and its potential activities could be assayed, proof of its physiological role remains elusive in the absence of a pure culture that can be genetically manipulated.

scholarly journals THE BEHAVIOR CHARACTERISTICS OF A RESERVOIR LEVEE SUBJECTED TO INCREASING WATER LEVELS

2017 ◽  
Vol 23 (1) ◽  
pp. 15-27
Author(s):  
Chung-Won LEE ◽  
Yong-Seong KIM ◽  
Sung-Yong PARK ◽  
Dong-Gyun KIM ◽  
Gunn HEO
Keyword(s):  
Hydraulic Fracturing ◽  
Real Time ◽  
Pore Water ◽  
Volumetric Strain ◽  
Water Levels ◽  
The Core ◽  
The Stability ◽  
Centrifugal Model ◽  
Behavior Characteristics ◽  
Plastic Volumetric Strain

Centrifugal model testing has been widely used to study the stability of levees. However, there have been a limited number of physical studies on levees where the velocity of increasing water levels was considered. To investigate the behavior characteristics of reservoir levees with different velocities of increasing water levels, centrifugal model tests and seepage-deformation coupled analyses were conducted. Through this study, it was confirmed that increasing water levels at higher velocities induces dramatic increases in the displacement, plastic volumetric strain and risk of hydraulic fracturing occurring in the core of the levee. Hence, real-time monitoring of the displacement and the pore water pres­sure of a levee is important to ensure levee stability.

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