Exploring carbon content variation in microplastics sequestrated from seawater to sediment in the Haima cold seep area
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Petroleum seep
Cold seep
Core sample
Carbon fibers
Studying deep-water cold seep systems is of great significance to gas hydrate exploration due to their close relationship. Various cold seep systems and related gas hydrate accumulations have been discovered in the northern South China Sea in the past three decades. Based on high-resolution seismic data, subbottom profiles, in situ submergence observations, deep drilling and coring, and hydrate gas geochemical analyses, the geological and geophysical characteristics of these cold seep systems and their associated gas hydrate accumulations in the Qiongdongnan Basin, the Shenhu area, the Dongsha area, and the Taixinan Basin have been investigated. Cold seep systems are present in diverse stages of evolution and exhibit various seabed microgeomorphic, geological, and geochemical features. Active cold seep systems with a large amount of gas leakage, gas plumes, and microbial communities and inactive cold seep systems with authigenic carbonate pavements are related to the variable intensity of the gas-bearing fluid, which is usually derived from the deep strata through mud diapirs, mud volcanoes, gas chimneys, and faults. Gas hydrates are usually precipitated in cold seep vents and deeper vertical fluid migration pathways, indicating that deep gas-bearing fluid activities control the formation and accumulation of gas hydrates. The hydrocarbons collected from cold seep systems and their associated gas hydrate reservoirs are generally mixtures of biogenic gas and thermogenic gas, the origin of which is generally consistent with that of deep conventional gas. We also discuss the paragenetic relationship between the gas-bearing fluid and the seafloor morphology of cold seeps and the deep-shallow coupling of gas hydrates, cold seeps, and deep petroleum reservoirs. It is reasonable to conclude that the deep petroleum systems and gas-bearing fluid activity jointly control the development of cold seep systems and the accumulation of gas hydrates in the northern South China Sea. Therefore, the favorable areas for conventional oil and gas enrichment are also prospective areas for exploring active cold seeps and gas hydrates.
Cold seep
Clathrate hydrate
Petroleum seep
Mud volcano
Authigenic
Seafloor Spreading
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Abstract The in situ detection and seafloor observation of the Site F cold seep began after its discovery. Research on deep−sea cold seep systems often begins with descriptions of topography and geomorphology. The earliest platform for topographic and geomorphologic exploration was the scientific expedition vessel. With the development of underwater vehicles, autonomous underwater vehicles (AUVs) and remote operated vehicles (ROVs) have become platforms for geophysical exploration of the seafloor. Thus, the spatial resolution of exploration has also been enhanced to the centimeter level. At the same time, sampling and in situ detection technology have gradually become the main research methods for cold seep systems. Based on the obtained samples and in situ data, research on the geochemistry and bioecology of cold seep systems has been carried out. Many technologies have been developed and may be used to promote the limit of detection of spectral−based methods to broaden the application range. Long−term detection for in situ experiments with specific scientific targets under natural cold seep environments is another trend for detection and observation in cold seep areas.
Petroleum seep
Cold seep
Seafloor Spreading
Remotely operated vehicle
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Cold seep
Petroleum seep
Chemosynthesis
Seafloor Spreading
Microbial mat
Rare-earth element
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Cold seeps in deep marine settings emit fluids to the overlying ocean and are often associated with such seafloor flux indicators as chemosynthetic biota, pockmarks, and authigenic carbonate rocks. Despite evidence for spatiotemporal variability in the rate, locus, and composition of cold seep fluid emissions, the shallow subseafloor plumbing systems have never been clearly imaged in three dimensions. Using a novel, high‐resolution approach, we produce the first three‐dimensional image of possible fluid conduits beneath a cold seep at a study site within the Blake Ridge gas hydrate province. Complex, dendritic features diverge upward toward the seafloor from feeder conduits at depth and could potentially draw flow laterally by up to 10 3 m from the known seafloor seep, a pattern similar to that suggested for some hydrothermal vents. The biodiversity, community structure, and succession dynamics of chemosynthetic communities at cold seeps may largely reflect these complexities of subseafloor fluid flow.
Cold seep
Chemosynthesis
Petroleum seep
Seafloor Spreading
Authigenic
Clathrate hydrate
Mud volcano
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Piston coring and trawling on the northern California continental slope (450–600 m) recovered shells and live organisms typical of a “cold” seep community. The presence of gas‐charged sediments, hydrates, and nearby oil seepage suggests that this habitat is like the hydrocarbon seeps of the Louisiana slope. Carbon, sulfur, and nitrogen isotopic compositions of organism tissues confirm the presence of bacterial chemosynthesis at these locations. This dicovery and previous reports suggest that the general occurrence of animals dependent on chemosynthesis is widespread.
Petroleum seep
Cold seep
Chemosynthesis
Coring
Carbon fibers
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Methane oxidizing archea(MOA) and sulfate reducing bacteria(SRB) are abundant in cold seep and hydrate sites,where dominant anaerobic oxidation of methane played an important role in the sea carbon cycle and microbial propagation.MOA oxidizes methane into HCO-3 and SRB reduces SO24 into HS-at gas seep site,which is anaerobic,and microbes obtain energy here for living and growth.At least MOA consists of three colonies:ANME-1,ANME-2 and ANME-3,showed in biomarkers as isoprenoids and free isoprenoid hydrocarbons.There are two colonies of SRB,that is,Desulfosarcina and Desulfococcus.The typical biomarkers produced by SRB are Dialkyl glycerol diethers(DGDs) and fatty acids.All the biomarkers of cold seep sites have very low carbon isotopic compositions which are between-41.1‰~-95.6‰,indicating that the microbes get carbon from CH4 and that there are activities of MOA and SRB in anaerobic gas seep sites.
Petroleum seep
Cold seep
Sulfate-Reducing Bacteria
Clathrate hydrate
Carbon fibers
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High resolution acoustic data, together with high-definition photomosaic images and video observations of the Formosa Ridge Cold Seep Site were obtained using a remotely operated vehicle (ROV). Seabed features of the cold seep site were described in detail and the scales and distribution patterns of these features displayed on the seabed were quantitatively analyzed. The cold seep site is characterized by irregular and hummocky topography on the seabed relief map and patches with high to medium backscatter intensities on side-scan sonar (SSS) images. Based on visual data, six kinds of seabed features related to cold seep activity were identified: gas flares, dense benthic chemosynthetic communities, mussel beds with low population densities, shells and/or shell debris areas, authigenic carbonate concretions, and reduced sediments. Spatially, these seabed features are distributed in an approximately zoned pattern with gas plumes and benthic communities in the innermost part of Site F and the reduced sediments in the outermost part. Based on the integrated acoustic and visual images and in-situ geochemical data, a conceptual model describing the cold seep fluid conduits within the shallow subsurface at Site F at the present is established. Briefly, favorable conduits have developed within the authigenic carbonate mound. The conduits channelize the cold seep fluids and result in relatively focused discharge of the seep fluids at the intersections of the conduits and the seabed, to sustain the dense communities there. Additionally, the authigenic carbonate concretions redirect some of the cold seep fluids to seeps at the periphery of the site, resulting in the reduced sediments. Integrated acoustic and visual investigations combined with in situ measurements are an effective way to quantitatively study the spatial extent of a cold seep site and can provide detailed information for further study of the cold seep system.
Petroleum seep
Cold seep
Seabed
Authigenic
Clathrate hydrate
Echo sounding
Remotely operated vehicle
Slumping
Seafloor Spreading
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We have analyzed the microbial communities in the cold-seep sediment samples obtained from different depths (5800∼7500 m) of the Japan Trench land slope. The results indicated that the typical cold-seep microbial communities of bacteria and archaea were basically similar in different depth environments and consisted of the delta-Proteobacteria (including sulfate reducing bacterial group) as well as methanogenic archaea, which played an important role in sulfur circulation in the seep environment. More abundant microbes were also identified in deeper cold-seep environments. These observations suggested that the cold-seep activity at the deepest depths of the Japan Trench might be more dynamic than in the shallower land slope. This is the first suggestion describing the relationship between microbial mass and cold-seep activity.
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Petroleum seep
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Cold seep ecosystems are characterized by a dense accumulation of chemosynthetic communities that utilize the chemical energy contained in fluids. Due to various technical challenges, the direct monitoring of these communities and their activity shifts during the venting of cold seeps has not been achieved. In this study, an integrated in-situ long-term observation platform was used to monitor seep venting activity, associated gas hydrates, and chemosynthetic communities inhabiting the Formosa Ridge in the South China Sea. In-situ Raman spectral data obtained over 14 days revealed two periods during which cold seep venting formed gas hydrates, interspersed with periods of hydrate decomposition during non-active intervals. The methane concentration in the open seawater column near the cold seep vent fluctuated, with an average of 23.07 μM (variance 28.71 μM). Furthermore, the average coverage ratio of the dominant cold seep macrofauna Shinkaia crosnieri was 22.94 % (variance 0.11 %). We hypothesize that the methane concentrations and biological cover in chemosynthetic communities exhibit stability. This phenomenon may be related to the role of natural gas hydrate deposits as methane capacitors, as proposed by earth scientists.
Chemosynthesis
Cold seep
Petroleum seep
Clathrate hydrate
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Cold seep communities discovered at three previously unknown sites between 600 and 1000 m in Monterey Bay, California, are dominated by chemoautotrophic bacteria (Beggiatoa sp.) and vesicomyid clams (5 sp.). Other seep-associated fauna included galatheid crabs (Munidopsis sp.), vestimentiferan worms (Lamellibrachia barhami?), solemyid clams (Solemya sp.), columbellid snails (Mitrella permodesta, Amphissa sp.), and pyropeltid limpets (Pyropelta sp.). More than 50 species of regional (i.e. non-seep) benthic fauna were also observed at seeps. Ratios of stable carbon isotopes (δ13C) in clam tissues near ∼ 36‰ indicate sulfur-oxidizing chemosynthetic production, rather than non-seep food sources, as their principal trophic pathway. The “Mt Crushmore” cold seep site is located in a vertically faulted and fractured region of the Pliocene Purisima Formation along the walls of Monterey Canyon (∼ 635 m), where seepage appears to derive from sulfide-rich fluids within the Purisima Formation. The “Clam Field” cold seep site, also in Monterey Canyon (∼ 900 m) is located near outcrops in the hydrocarbon-bearing Monterey Formation. Chemosynthetic communities were also found at an accretionary-like prism on the continental slope near 1000 m depth (Clam Flat site). Fluid flow at the “Clam Flat” site is thought to represent dewatering of accretionary sediments by tectonic compression, or hydrocarbon formation at depth, or both. Sulfide levels in pore waters were low at Mt Crushmore (ca ∼ ∼ 0.2 mM), and high at the two deeper sites (ca 7.011.0 mM). Methane was not detected at the Mt Crushmore site, but ranged from 0.06 to 2.0 mM at the other sites.
Chemosynthesis
Petroleum seep
Cold seep
Submarine canyon
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