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1.
Three sectors of the south Barbados prism between 1000 and 2000 m depth were explored by the French submersible Nautile. Chemosynthesis-based benthic communities were discovered on several structures affected by diapirism, including mud volcanoes, domes and an anticlinal ridge. The communities are associated with the expulsion of methane-rich fluids which is a wide-spread process in the area. These communities are dominated by large bivalves and vestimentiferans which harbour chemoautotrophic symbiotic bacteria. The symbiotic bivalves include two species of Mytilidae and one of Vesicomyidae, with dominance of a methanotrophic mussel. Cartography of the benthic communities, interpretation of thermal measurements and observation of sedimentary patterns have been used to define the life habits of each of the three species of symbiotic bivalves. Each species has a characteristic preference for different conditions of edaphic and fluid flow: the dominant methanotrophic mussel appears to require high velocity vents and hard substratum. The vesicomyids and the other species of mussel are able to take up sulfide from the sediments, and so are associated with low seepages, but also require soft sediment. The three bivalve species are assumed successively to colonize the top of a diapiric ridge, in a succession related to the temporal evolution of fluid flow and sedimentation. The composition of the bivalve assemblages, their densities and biomasses all differ between the several mud volcanoes and domes studied, and these parameters are thought to be related to the spatial and temporal variations of fluid expulsion through the structures, and the lithification processes linked to fluid expulsion. One very active dome is at present colonized by an exceptionally large and dense population of the methanotrophic mussel. In contrast, communities in another area, on the domes and volcanoes that are currently inactive, were colonized by only a few living vesicomyids and mussels, both associated with sulfur-oxydizing bacteria, and there were numerous empty shells. The densities and biomasses of symbiotic bivalves were far greater in the area studied than in a deeper mud volcano field on the same prism that had been studied previously. This is consistent with a report that methane production is greater in the southern region of this accretionary prism than in the northern. Numerous non-symbiotic organisms were observed in and around the areas of the seeps, some are endemic to the seep communities, including some gastropods and shrimps, others are either colonists or vagrants from the surrounding deep-sea floor. Filter feeders were very abundant, and some of these, like the serpulids and large sponges, may also be dependent on the chemosynthetic production. Faunistic composition of both symbiotic and non-symbiotic taxa, of the assemblages around these cold seeps, is closely related to that reported for communities living on hydrocarbon seeps in the Gulf of Mexico.  相似文献   

2.
To estimate the degree of spatial heterogeneity of benthic deep-sea communities, we carried out a multiple-scale (from m's to 200 km) investigation in the Congo-Angola margins (Equatorial West African margin, 3150–4800 m) in which we examined the metazoan meiofauna at a variety of habitats along the Congo Channel system and in the associated cold seep. We investigate the structure, density, vertical distribution patterns in the sediment and biomass of meiofaunal communities in the Gulf of Guinea and how they are controlled by hydrologic and biogeochemical processes. The meiofaunal communities in the Gulf of Guinea were shaped by heterogeneous conditions on the margin, and reflect the multiple-scale spatial variability that corresponds with the different identified habitats. The two control sites, located at >100 km away from the canyon, were inhabited by very dense and the most diverse meiobenthic communities. Similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep. Sites located along the Congo Channel were obviously affected by the local high-velocity bottom currents and unstable sedimentary conditions in this active submarine system. Extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites. The remote operated vehicle (ROV) Victor 6000 provided images of the cold seep, showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa (Mytilidae, Vesicomyidae and Siboglinidae). These cold seep sediments were colonised by a unique meiobenthic community, characterised by a high small-scale (m's) patchiness, low species richness and the prominent dominance of two large-sized nematode species: Sabatieria mortenseni, which is a cosmopolitan nematode known from littoral habitats, and an undescribed Desmodora species. The high individual body weight of S. mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites. In addition, the vertical nematode profiles, with maximum proportions in subsurficial layers, points to a chemosynthesis-based meiobenthic community in this cold seep, in contrast to the phytodetritus-based communities at the control sites and at the transition zone.  相似文献   

3.
Quantitative collections of tubeworm- and mussel-associated communities were obtained from 3 cold seep sites in the deep Gulf of Mexico: in Atwater Valley at 1890 m depth, in Alaminos Canyon at 2200 m depth, and from the Florida Escarpment at 3300 m depth. A total of 50 taxa of macro- and megafauna were collected including 2 species of siboglinid tubeworms and 3 species of bathymodiolin mussels. In general, the highest degree of similarity was between communities collected from the same site. Most of the dominant families at the well-characterized upper Louisiana slope seep sites of the Gulf of Mexico were present at the deep sites as well; however, there was little overlap at the species level between the upper and lower slope communities. One major difference in community structure between the upper and lower slope seeps was the dominance of the ophiuroid Ophioctenella acies in the deeper communities. The transition between upper and lower slope communities appears to occur between 1300 and 1700 m based on the number of shared species with the Barbados seeps at either end of this depth range. Seep communities of the deep Gulf of Mexico were more similar to the Barbados Accretionary Prism seep communities than they were to either the upper slope Gulf of Mexico or Blake Ridge communities based on numbers of shared species and Bray–Curtis similarity values among sites. The presence of shared species among these sites suggests that there is ongoing or recent exchange among these areas. An analysis of bathymodioline mussel phylogeography that includes new collections from the west coast of Africa is presented. This analysis also suggests recent exchange across the Atlantic equatorial belt from the Gulf of Mexico to the seeps of the West Nigerian margin.  相似文献   

4.
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.  相似文献   

5.
The San Clemente cold seep lies within 100–200 km of other reducing habitats in the NE Pacific, offering an opportunity to compare diversity and species overlap among reducing habitats (i.e. whale‐, kelp‐, and wood‐falls) at similar depths within a single region. Video observations from the research submersible Alvin at the San Clemente seep (1800 m depth) indicated clumps (‘thickets’) of vestimentiferans distributed as meter‐scale patches interspersed with vesicomyid clam beds and black sediments. Sediment‐core samples were collected at distances of 0 to 80–200 m along randomly oriented transects radiating outward from vestimentiferan thickets to evaluate changes in macrofaunal community structure from thickets into the background community. Macrofaunal abundance was elevated at distances of 0–1 m compared to 80–200 m (i.e. the ‘background’ community). The tube‐building frenulate worms Siboglinum spp., along with peracarid crustaceans, dominated sediments within 1 m of vestimentiferan thickets. Species diversity was depressed within 1 m of thickets but with high rates of species accumulation, suggesting that seep sites greatly increase sediment heterogeneity and facilitate colonization by non‐background macrofaunal species. Stable isotope data indicate chemosynthetic nutrition for some dominant macrofaunal species within 1 m of tubeworm thickets. The macrofaunal community near vestimentiferan thickets in San Clemente seep contains intermediate levels of species richness and diversity compared to other deep‐sea seep areas in the northeast Pacific. There was low species overlap between the San Clemente seep macrofauna and communities in reducing habitats near wood‐, whale‐, and kelp‐falls at similar depths within the region, suggesting that seeps harbor a distinct infaunal community.  相似文献   

6.
Meiofauna in a cold-seep community off Hatsushima,central Japan   总被引：2，自引：0，他引：2  
The community structure of the bathyal meiofauna of a cold-seep community found off Hatsushima in Sagami Bay, central Japan, was compared with the community composition outside the influence of the seep, using sediments collected during dives 226 and 227 of the deep-sea submersibleShinkai 2000. The sediment from the Hatsushima seep site (HSS) was very coarse, black in color, and with an odor of hydrogen sulfide, suggesting reduced thiobiotic conditions. The sediment from the control area was well-oxygenated, fine silt. Despite the differences in the characteristics of the sediments, the abundance of meiofauna in the HSS was not very different from that in the control area. However, its composition even at the major taxonomic group level was distinct; for example, a high nematode/copepod ratio occurred in one of the samples collected at the HSS. At the species level, nematodes were less diverse at the HSS than at the control area. The composition of the nematode fauna at the HSS showed stronger affinity with that collected at the adjacent control area than with a community sampled from other deep-sea environments or another seep community in shallow water. This emphasizes that the adaptation of nematodes to the thiobiotic condition is controlled by local conditions.  相似文献   

7.
Bathymodiolus属贻贝是广泛分布于全球深海冷泉和热液生态系统的优势种,在深海化能生态系统的物质循环和能量流动中起着重要作用。本文以我国南海北部冷泉的主要优势种平端深海偏顶蛤(Bathymodiolus platifrons)为研究对象,采用常规生化测定方法,研究了其主要生化成分和氨基酸组成的特征,并就特定组织中主要生化成分的含量与生活在热液区的平端深海偏顶蛤和近岸的远东偏顶蛤(Modiolus kurilensis)进行了对比。结果表明,南海冷泉平端深海偏顶蛤软体部含水量84.28%,粗蛋白含量7.18%,粗脂肪含量1.23%,糖类含量2.75%,与已报道的深海贝类组成相近。虽然主要生化成分含量在3种贻贝的鳃、外套膜、闭壳肌和消化腺4个组织中总体差异不大,但是冷泉平端深海偏顶蛤和热液平端深海偏顶蛤的外套膜糖类含量(25.20%、30.66%)显著高于远东偏顶蛤(6.97%,P0.05),这表明平端深海偏顶蛤的主要储存物质为外套膜中的糖类。在氨基酸组成上,冷泉平端深海偏顶蛤鳃中氨基酸总量为44.55%(干质量),外套膜中为34.83%(干质量),其中必需氨基酸分别占比41.73%和40.52%,总体与其他贝类相似。然而,在平端深海偏顶蛤中,与渗透压调节相关的甘氨酸和与硫代谢相关的牛磺酸含量较高,这与其适应深海高盐度高硫化氢浓度的环境相关。综上所述,南海冷泉平端深海偏顶蛤在常规生化组分和氨基酸组成上与近岸常见双壳类具有一定差异,这些差异与其特殊生境的关系还需要更加深入的研究。  相似文献   

8.
平端深海偏顶蛤(Gigantidasplatifrons)是广泛分布于西太平洋深海热液和冷泉生态系统中的优势种和共有种,也是深海化能生态系统中重要的生境营造种。以南海F冷泉平端深海偏顶蛤为研究对象,基于贝壳日生长轮方法,分析了平端深海偏顶蛤的年龄与生长速率,建立了其年龄与贝壳壳长关系的生长方程。同时,结合获得的生长方程,分析了南海F冷泉采样点(119.285 6°E,22.115 4°N)平端深海偏顶蛤种群的年龄结构。研究结果表明,采样获得的平端深海偏顶蛤种群的最大壳长为11.4 cm,最大寿命为13.5龄。研究区域的贝壳长度分布集中在4～7 cm,占比60%;年龄分布集中在2～4龄,占比49.7%。相关研究结果为进一步开展平端深海偏顶蛤的生长研究提供了基础数据,有助于深入了解冷泉区域的种群动态变化规律。  相似文献   

9.
台湾岛西南海域福尔摩沙海脊冷泉区地形地貌特征分析   总被引：2，自引：0，他引：2  
利用水深数据和ROV近海底影像资料,对福尔摩沙海脊冷泉区的海底地形地貌和冷泉系统的海底表征进行了描述和分析,并讨论了二者之间的响应关系。结果表明,相对于船载多波束数据而言,近海底多波束测深系统所获得的数据能更高精度地反映冷泉区海底地形地貌特征,是研究冷泉系统不可或缺的基础资料。基于ROV近海底观测影像资料,福尔摩沙海脊冷泉系统整体表现为局部被化能自养生物群落覆盖并有流体喷口零星分布的巨大自生碳酸盐岩岩丘,海底表征主要包括形态各异的自生碳酸盐岩结壳或岩体、化能自养生物群落、流体喷口、还原性沉积物等几种形式。研究表明,福尔摩沙海脊冷泉区的地形地貌特征与冷泉系统海底表征具有良好的响应关系,并且该区的地形地貌特征主要受控于出露于海底的自生碳酸盐岩的形态特征及规模。首次揭示了福尔摩沙海脊冷泉区地形地貌特征与其海底表征之间的响应关系,以期为后续的冷泉研究提供必要的背景资料支持。  相似文献   

10.
Multi-scale reflection seismic data, from deep-penetration to high-resolution, have been analyzed and integrated with near-surface geophysical and geochemical data to investigate the structures and gas hydrate system of the Formosa Ridge offshore of southwestern Taiwan. In 2007, dense and large chemosynthetic communities were discovered on top of the Formosa Ridge at water depth of 1125 m by the ROV Hyper-Dolphin. A continuous and strong BSR has been observed on seismic profiles from 300 to 500 ms two-way-travel-time below the seafloor of this ridge. Sedimentary strata of the Formosa Ridge are generally flat lying which suggests that this ridge was formed by submarine erosion processes of down-slope canyon development. In addition, some sediment waves and mass wasting features are present on the ridge. Beneath the cold seep site, a vertical blanking zone, or seismic chimney, is clearly observed on seismic profiles, and it is interpreted to be a fluid conduit. A thick low velocity zone beneath BSR suggests the presence of a gas reservoir there. This “gas reservoir” is shallower than the surrounding canyon floors along the ridge; therefore as warm methane-rich fluids inside the ridge migrate upward, sulfate carried by cold sea water can flow into the fluid system from both flanks of the ridge. This process may drive a fluid circulation system and the active cold seep site which emits both hydrogen sulfide and methane to feed the chemosynthetic communities.  相似文献   

11.
Fifty protease-producing strains were screened from sediment of deep-sea cold seep,and divided into four different categories:Bacillus,Pseudoalteromonas,Vibrio,...  相似文献   

12.
随着海洋调查技术的发展和海洋研究的深入,基于深潜器平台的近海底调查在海洋调查与研究中的综合应用日趋常态。基于这一背景,本文介绍了搭载于"发现"号缆控水下机器人(remotely operatedvehicle,ROV)的近海底综合声学调查系统及其在台西南冷泉区的应用实例。基于"发现"号ROV平台的近海底综合声学调查系统主要由R2Sonic2024多波束测深系统,模块一体化的侧扫声纳-浅地层剖面系统和水下综合定位与导航系统构成。该系统的配置极大地扩展和完善了"发现"号ROV的近海底调查能力,实现了近海底多波束、侧扫和浅剖等声学数据的同步采集和快速融合处理。基于本套系统在南海冷泉区的综合应用,本文对其工作流程进行了介绍,并对所获得一系列成果进行了初步分析。结果表明,近海底综合探测系统的应用为南海冷泉区的识别、海底地形地貌特征分析以及空间规模量化研究等内容提供了不可或缺的基础资料。本套系统的配置和成功应用,有效地提高了我国的近海底调查和作业能力。  相似文献   

13.
Based on high-resolution Chirp seismic, multibeam bathymetry and side scan sonar data collected in the ?zmir Gulf, Aegean Sea in 2008 and 2010, gas-related structures have been identified, which can be classified into three categories: (1) shallow gas accumulations and gas chimneys, (2) mud diapirs, and (3) active and inactive pockmarks. On the Chirp profiles, shallow gas accumulations were observed along the northern coastline of the outer ?zmir Gulf at 3-20 m below the seabed. They appear as acoustic turbidity zones and are interpreted as biogenic gas accumulations produced in organic-rich highstand fan sediments from the Gediz River. The diapiric structures are interpreted as shale or mud diapirs formed under lateral compression due to regional counter-clockwise rotation of Anatolian microplate. Furthermore, the sedimentary structure at the flanks suggests a continuous upward movement of the diapirs. Several pockmarks exist close to fault traces to the east of Hekim Island; most of them were associated with acoustic plumes indicating active degassing during the survey period in 2008. Another Chirp survey was carried out just over these plumes in 2010 to demonstrate if the gas seeps were still active. The surveys indicate that the gas seep is an ongoing process in the gulf. Based on the Chirp data, we proposed that the pockmark formation in the area can be explained by protracted seep model, whereby sediment erosion and re-distribution along pockmark walls result from ongoing (or long lasting) seepage of fluids over long periods of time. The existence of inactive pockmarks in the vicinity, however, implies that gas seepage may eventually cease or that it is periodic. Most of the active pockmarks are located over the fault planes, likely indicating that the gas seepage is controlled by active faulting.  相似文献   

14.
The West Alboran Basin was previously classified as a mud volcanic province consisting of two mud volcano (MV) fields that are inactive at the present day: the Northern (Spanish) and the Southern (Moroccan) fields. The discovery of the first active mud volcano (Carmen; cruise TTR-17) in 2008, along with several pockmarks at the central part of the basin, motivates more careful geological and geochemical analysis of previous data and comparison to new observations.Gas bubbling from the crater of Carmen MV was observed and recorded using an underwater TV-system and a large TV-grab sample. The gas mainly consisted of methane with less than 1% wetness. However, all sets of homologues up to pentane were detected in the mud breccia of Carmen MV. Both molecular and stable carbon isotopic compositions, and their distribution along the core length, suggest a deep thermogenic source of hydrocarbons (HCs). Composition of the pore water from Carmen MV also points to a deep source of mud volcanic water. The isotopic results indicate that the source of mud volcanic water is the dehydration of clay minerals in the thermal zone of the smectite-to-illite transformation. Our observations allow us to infer the presence of structure II gas hydrates in mud breccia on the top of Carmen MV.High HC gas saturation in sediments in some pockmarks accompanied with live chemosynthetic fauna directly indicates the strong seepage activity of these structures. For the first time, authigenic carbonate crusts and chimneys with associated living chemosynthetic bivalves and tubeworms were sampled from a seep site in the West Alboran Sea. Authigenic carbonates consist of aragonite and calcite, and are characterized by a light carbon isotopic signature, up to −37.2‰ PDB, which points to their methane-derived origin.  相似文献   

15.
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16.
基因组大小(或称C值)作为生物单倍体细胞中全套染色体的DNA总量,在一定程度上是恒定的,因而C值可以作为生物物种的一个特定参数。深海热液和冷泉为更好地理解C值与不同环境之间的关系提供了一个特征性的模型。本文采用流式细胞术,测定了来自热液和冷泉环境中的10种深海无脊椎动物的C值,其分布范围从0.87 pg到12.28 pg,其中,相比于软体动物和多毛类,甲壳生物基因组大小及变异均较大。对比热液和冷泉两个群落中共有种(深海偏顶蛤Bathymodiolus platifrons、柯氏潜铠虾Shinkaia crosnieri以及长角阿尔文虾Alvinocaris longirostris)的基因组大小,发现C值差异并不显著。同时,综合已有的数据,对深海化能极端环境与其他环境条件下的物种C值进行对比分析,结果显示深海化能极端环境下生物的基因组大小并没有发现明确的变化趋势。  相似文献   

17.
Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200–3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep‐water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow‐seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane‐derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 ± 11,618 ind·m−2), the lowest in the Florida pogonophoran fields (926 ± 132 ind·m−2), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non‐seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (>60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H′) was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non‐seep sediments. Community composition differences between seep and non‐seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep δ13C and δ15N signatures were lighter for seep than non‐seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest δ13C values (average of species’ means) were observed at the Florida escarpment (−42.8‰). We estimated that on average animal tissues had up to 55% methane‐derived carbon in Florida mats, 31–44% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9–23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific δ13C variation (>30‰) between patch types. Overall we found few characteristic communities or features common to the three deep‐water seeps (>3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon.  相似文献   

18.
The abundance and higher taxonomic composition of epizooic metazoan meiobenthic communities associated with mussel and tubeworm aggregations of hydrocarbon seeps at Green Canyon, Atwater Valley, and Alaminos Canyon in depths between 1400 and 2800?m were studied and compared to the infaunal community of non-seep sediments nearby. Epizooic meiofaunal abundances of associated meiobenthos living in tubeworm bushes and mussel beds at seeps were extremely low (usually <100?ind. 10?cm(-2)), similar to epizooic meiofauna at deep-sea hydrothermal vents, and the communities were composed primarily of nematodes, copepods, ostracods, and halacarids. In contrast, epizooic meiobenthic abundance is lower than previous studies have reported for infauna from seep sediments. Interestingly, non-seep sediments contained higher abundances and higher taxonomic diversity than epizooic seep communities, although in situ primary production is restricted to seeps.  相似文献   

19.
Mud volcanoes (MVs) are abundant along the eastern Mediterranean subduction zones, recording mud breccia extrusion over long timescales (106 years), but to date relatively few have been recognised in the northern Ionian Sea on the Calabrian accretionary prism (CAP). In the present study, the seafloor distribution and recent activity of MVs is investigated across a 35,600 km2 sector of the CAP using a regional acoustic dataset (multibeam bathymetric and backscatter imagery, integrated with subbottom profiles) locally ground-truthed by sediment cores. A total of 54 MVs are identified across water depths of 150–2,750 m using up to four geophysical criteria: distinctive morphology, high backscatter, unstratified subbottom facies and, in one case, a hydroacoustic flare. Fourteen MVs are identified from 3–4 criteria, of which five have been previously proven by cores containing mud breccia beneath up to 1.6 m of hemipelagic sediments (Madonna dello Ionio MVs 1–3, Pythagoras MV and the newly named Sartori MV), while nine others are identified for the first time (Athena, Catanzaro, Cerere, Diana, Giunone, Minerva, ‘right foot’, Venere 1 and 2). Forty other as yet unnamed MVs are inferred from 1–2 geophysical criteria (three from distinctive morphology alone). All but one possible MV lie on the inner plateau of the CAP, landwards of the Calabrian Escarpment in a zone up to 120 km wide that includes the inner pre-Messinian wedge and the fore-arc basins, where they are interpreted to record the ascent from depth of overpressured fluids that interacted with tectonic structures and with evaporitic or shale seals within the fore-arc basins. The rise of fluids may have been triggered by post-Messinian out-of-sequence tectonism that affected the entire pre-Messinian prism, but Plio-Quaternary sedimentation rates and depositional styles support the inference that significant mud volcanism has taken place only on the inner plateau. Sedimentation rates across the CAP applied to a 12 khz sonar detection depth of 225 cm imply that all MVs with backscatter signatures (50 of 54) have erupted mud breccias within the last 56 ka, and within the last 12.5 ka in the fore-arc basins. Ages of eruption estimated from the depth of cored mud breccias at five MVs, and a seismo-stratigraphic relationship at a sixth, indicate episodes at the last glacial maximum ca. 20 ka BP and during the postglacial period. Eruptive episodes within the Calabrian MV province constitute recurrent geohazards, separated by longer periods of quiescent (subdued) fluid seepage that are likely to support gas hydrate formation and chemosynthetic ecosystems.  相似文献   

20.
Tubeworms within the annelid family Siboglinidae rely on sulfur-oxidizing autotrophic bacterial symbionts for their nutrition, and are among the dominant metazoans occurring at deep-sea hydrocarbon seeps. Contrary to their relatives from hydrothermal vents, sulfide uptake for symbionts occurs within the anoxic subsurface sediment, in the posterior ‘root’ region of the animal. This study reports on an integrated microbiological and geochemical investigation of the cold seep tubeworm Escarpia southwardae collected at the Regab pockmark (Gulf of Guinea). Our aim was to further constrain the links between the animal and its symbiotic bacteria, and their environment. We show that E. southwardae harbors abundant sulfur-oxidizing bacterial symbionts in its trophosome. Symbionts are able to fix inorganic carbon using the Calvin-Benson cycle, as reported in most other Siboglinidae, but can also use the reverse Tricarboxilic Acid Cycle. Surprisingly, the observed bacteria appear to be more closely related to symbionts of Escarpia and Lamellibrachia species from very distant sites located in the Gulf of Mexico and eastern Pacific, than to symbionts of a siboglinid occurring at a nearby methane seep site, only a few hundred km away from Regab. Then, by combining scanning electron microscopy and trace element (Mn, Fe, Sr, Zr) analyses of E. southwardae tube, we also show that two distinct oxidation fronts occur along the tube. The first one, near the posterior end of the tube, corresponds to the interface between oxic bottom waters and the underlying anoxic sediment. In contrast, the second redox front is located in the most anterior part of the tube, and could result from active oxygen uptake by the plume of the tubeworm. We speculate that intense oxygen consumption in this region could create favorable conditions for sulfate reduction by specialized bacteria associated with the plume, possibly leading to an additional source of dissolved sulfide that would further enhance the productivity of bacterial symbionts.  相似文献   

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