Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea

Reitz, Anja; Pape, Thomas; Haeckel, Matthias; Schmidt, Mark; Berner, Ulrich; Scholz, Florian; Liebetrau, Volker; Aloisi, Giovanni; Weise, Stephan M.; Wallmann, Klaus

doi:10.1016/j.gca.2011.03.018

Cited by 53 publications

(36 citation statements)

References 111 publications

(177 reference statements)

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“…Wallmann et al, 1997Wallmann et al, , 2006Suess et al, 1998;Tryon et al, 1999;Sahling et al, 2008;Niemann et al, 2009;Reitz et al, 2011). The upward supply of hydrocarbons towards and across the sediment/water interface produces steep geochemical gradients of pore water constituents, and typically stimulates high rates of anaerobic oxidation of methane (AOM) and other hydrocarbons with sulfate as an electron acceptor close to the sediment surface (Borowski et al, 1996;Treude et al, 2003).…”

Section: Fischer Et Al: Pore Water Geochemistry Of Cold Seeps Offmentioning

confidence: 99%

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

et al. 2012

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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 thatin 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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Section: Fischer Et Al: Pore Water Geochemistry Of Cold Seeps Offmentioning

confidence: 99%

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

et al. 2012

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“…These field works were carried in this area in 2005 as part of a UNESCO training and research program as well as in 2007 and in 2011 within the German Methane and Methane Hydrates (METRO) project. Investigations on the south-eastern continental slope [41,42] have shown that there are gas jet seepages where methane coexists simultaneously in free form and as gas hydrates, which is very unique for the Black Sea. The characteristic feature of these seepages is the presence of oil traces in the seabed gas hydrates.…”

Section: Introductionmentioning

confidence: 99%

Satellite Survey of Inner Seas: Oil Pollution in the Black and Caspian Seas

Mityagina

Lavrova

2016

Remote Sensing

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Abstract:The paper discusses our studies of oil pollution in the Black and Caspian Seas. The research was based on a multi-sensor approach on satellite survey data. A combined analysis of oil film signatures in satellite synthetic aperture radar (SAR) and optical imagery was performed. Maps of oil spills detected in satellite imagery of the whole aquatic area of the Black Sea and the Middle and the Southern Caspian Sea are created. Areas of the heaviest pollution are outlined. It is shown that the main types of sea surface oil pollution are ship discharges and natural marine hydrocarbon seepages. For each type of pollution and each sea, regions of regular pollution occurrence were determined, polluted areas were estimated, and specific manifestation features were revealed.Long-term observations demonstrate that in recent years, illegal wastewater discharges into the Black Sea have become very common, which raises serious environmental issues. Manifestations of seabed hydrocarbon seepages were also detected in the Black Sea, primarily in its eastern part. The patterns of surface oil pollution of the Caspian Sea differ considerably from those observed in the Black Sea. They are largely determined by presence of big seabed oil and gas deposits. The dependence of surface oil SAR signatures on wind/wave conditions is discussed. The impact of dynamic and circulation processes on oil films drift and spread is investigated. A large amount of the data available allowed us to make some generalizations and obtain statistically significant results on spatial and temporal variability of various surface film manifestations. The examples and numerical data we provide on ship spills and seabed seepages reflect the influence of the pollution on the sea environment.

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“…This is in good agreement with porewater analysis on sediment cores from the same sites. Here Li, B, δ 18 O and 87/86 Sr propose a fluid source with temperatures >100 • C from smectite-illite transformation only at Pechori Mound (Reitz et al, 2011). The difference in gas compositions at the two sites is strongly expressed in the gas hydrate composition (Table 4).…”

Section: Gas Compositions Derived From Pressure Coringmentioning

confidence: 90%

“…A complete model description can be found in Appendix A. A detailed analysis and discussion of the measured and modeled porewater data from this area was published in Reitz et al (2011).…”

Section: Modeling the Chloride Anomaly For Its Relation To The Hydratmentioning

confidence: 99%

Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique

et al. 2011

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Abstract. In the eastern Black Sea, we determined methane (CH 4 ) concentrations, gas hydrate volumes, and their vertical distribution from combined gas and chloride (Cl − ) measurements within pressurized sediment cores. The total gas volume collected from the cores corresponded to concentrations of 1.2-1.4 mol CH 4 kg −1 porewater at in-situ pressure, which is equivalent to a gas hydrate saturation of 15-18 % of pore volume and amongst the highest values detected in shallow seep sediments. At the central seep site, a highresolution Cl − profile resolved the upper boundary of gas hydrate occurrence and a continuous layer of hydrates in a sediment column of 120 cm thickness. Including this information, a more precise gas hydrate saturation of 22-24 % pore volume could be calculated. This volume was higher in comparison to a saturation calculated from the Cl − profile alone, resulting in only 14.4 %. The likely explanation is an active gas hydrate formation from CH 4 gas ebullition. The hydrocarbons at Batumi Seep are of shallow biogenic origin (CH 4 > 99.6 %), at Pechori Mound they originate from deeper thermocatalytic processes as indicated by the lower ratios of C 1 to C 2 -C 3 and the presence of C 5 .

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Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea

Cited by 53 publications

References 111 publications

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

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

Satellite Survey of Inner Seas: Oil Pollution in the Black and Caspian Seas

Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique

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