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1.
Gettysburg and Ormonde are two shallow peaks located on the Gorringe seamount about 200 and 240 km WSW off Cape St. Vincent (Portugal, NE Atlantic), within the Portuguese Economic Exclusive Zone. Despite the ecological importance of the biological assemblages on these peaks and the need to preserve seamounts as valuable habitats, no management plans have been yet implemented at this site, which only recently has been included in the list of Sites of Community Importance of Portugal. Video imagery collected using a ROV during the 2011 Oceana campaigns was used here to analyse qualitative and quantitative patterns of benthic assemblage composition at the summit of the seamount (between 30 and 230 m depth). The results suggest that Ormonde is a biologically important area made up of vulnerable marine ecosystem elements that change significantly with depth. These include: kelp beds, in the euphotic zone; encrusting coralline algal communities and solitary colonies or mixed associations of suspension‐feeders (scleractinians, gorgonians, antipatharians, encrusting demosponges and ascidians), at the lower limit of the euphotic zone; mixed coral gardens and erect sponges, in the disphotic zone; and dense sponge aggregations, on the upper slope. These results were further used to propose amendments to the European Nature Information System habitat classification as a tool to work towards resolving the seamounts management issue. The results also provide information on taxa and habitats with high ecological value and classified as threatened or vulnerable, which is essential for the implementation of the cornerstones of Europe's biodiversity conservation policy, namely the OSPAR Convention and the EU Habitats Directive.  相似文献   

2.
Given the advances in satellite altimetry and multibeam bathymetry, benthic terrain classification based on digital bathymetric models (DBMs) has been widely used for the mapping of benthic topographies. For instance, cobalt-rich crusts (CRCs) are important mineral resources found on seamounts and guyots in the western Pacific Ocean. Thick, plate-like CRCs are known to form on the summit and slopes of seamounts at the 1 000–3 000 m depth, while the relationship between seamount topography and spatial distribution of CRCs remains unclear. The benthic terrain classification of seamounts can solve this problem, thereby, facilitating the rapid exploration of seamount CRCs. Our study used an EM122 multibeam echosounder to retrieve high-resolution bathymetry data in the CRCs contract license area of China, i.e., the Jiaxie Guyots in 2015 and 2016. Based on the DBM construted by bathymetirc data, broad- and fine-scale bathymetric position indices were utilized for quantitative classification of the terrain units of the Jiaxie Guyots on multiple scales. The classification revealed four first-order terrain units (e.g., flat, crest, slope, and depression) and eleven second-order terrain units (e.g., local crests, depressions on crests, gentle slopes, crests on slopes, and local depressions, etc.). Furthermore, the classification of the terrain and geological analysis indicated that the Weijia Guyot has a large flat summit, with local crests at the southern summit, whereas most of the guyot flanks were covered by gentle slopes. “Radial” mountain ridges have developed on the eastern side, while large-scale gravitational landslides have developed on the western and southern flanks. Additionally, landslide masses can be observed at the bottom of these slopes. The coverage of local crests on the seamount is ~1 000 km2, and the local crests on the peak and flanks of the guyots may be the areas where thick and continuous plate-like CRCs are likely to occur.  相似文献   

3.
Scientific study has generated a range of hypotheses about the ecological structure and function of seamounts. Interpretations of these ideas and data are vital to understanding how seamount communities will respond to anthropogenic impacts. Here, we examine how diversity and structure of seamount assemblages vary with depth and slope of the sea floor. We conducted ROV video transects on three seamounts of the Taney Seamount Chain in the Northeast Pacific Ocean. Depth and slope were both related to assemblage structure on the Taney seamounts. Depth differences were seen in alpha‐ and beta‐diversity but not density. Beta‐diversity and density but not alpha‐diversity varied with slope. Overall, slope and depth together explained 14–31% of beta‐diversity. The findings suggest that differences in beta‐diversity as related to depth gradients may differ among onshore and offshore and/or between shallow and deep summit seamounts. Specifically, we hypothesize that differences in productivity and depth gradients among seamounts may generate different patterns of beta‐diversity.  相似文献   

4.
Most of the Southeast Atlantic Ocean is abyssal, and global bathymetries suggest that only ～3.2% of the areas beyond national jurisdiction (ABNJ; also known as the high seas, as defined in the United Nations Convention on the Law of the Sea [UNCLOS]) are shallower than 2 500 m. This study mapped bathymetry and characterised substrates in selected seamount summit areas, including several that have been or may become fishing areas. The southernmost location, the Schmitt-Ott Seamount, has exposed volcanic bedrock with surrounding flats covered by thin biogenic sediments and/or coral rubble that appears ancient. At Wüst, Vema, Valdivia and Ewing seamounts the basaltic base appears to be overlain by coral caps and other coral substrates (sheets, rubble). Adjacent summit plains have biogenic sediments of varying thickness. Vema has a flat, roughly circular summit, <100 m deep, with the shallowest point being a 22-m-deep summit knoll; the upper slopes have ancient coral framework, but the summit has a mixture of coralline and volcanic rock and coarse sediments, including extensive areas with coralline algae and kelp forests. Valdivia Bank is a 230-m-deep, flat, rocky area (～11 × 5 km), protruding steeply from the extensive multi-summit Valdivia subarea of the Walvis Ridge. The distribution of past fisheries in the Convention Area of the South East Atlantic Fisheries Organisation (SEAFO) was considered in relation to the new information on bathymetry and substrate.  相似文献   

5.
Observations from 17 ALVIN dives and 14 ANGUS runs plus laboratory study of basalt samples collected with ALVIN help to constrain the morphologic, volcanic and petrologic evolution of four seamounts near the East Pacific Rise (EPR). Comparison among the four volcanoes provides evidence for a general pattern of near-EPR seamount evolution and shows the importance of sedimentation, mass wasting, hydrothermal activity and other geologic processes that occur on submerged oceanic volcanoes. Seamount 5, closest to the EPR (1.0 Ma) is the youngest seamount and may still be active. Its summit is covered by fresh lavas, recent faults and hydrothermal deposits. Seamount D is on crust 1.55 Ma and is inactive; like seamount 5, it has a breached caldera and is composed exclusively of N-MORB. Seamounts 5 and D represent the last stages of growth of typical N-MORB-only seamounts near the EPR axis. Seamounts 6 and 7 have bumpy, flattish summits composed of transitional and alkalic lavas. These lavas probably represent caldera fillings and caps overlying an edifice composed of N-MORB. Evolution from N-MORB-only cratered edifices to the alkalic stage does not occur on all near-EPR seamounts and may be favored by location on structures with relative-motion-parallel orientation.  相似文献   

6.
中西太平洋海山形态类型与钴结壳资源分布关系   总被引：4，自引：1，他引：3       下载免费PDF全文
通过对中西太平洋海山形态剖面的山体高度、山顶直径、基底直径、山顶直径与基底直径之比、山体坡度、山体高度与基底直径比值六个参数多元统计分析,发现可以根据山体高度与基底直径的比值对海山形态类型进行分类:比值小于0.10的为平顶海山(Ⅰ类),大于0.10的为尖顶海山(Ⅱ类),对于等于0.10的海山需参考平坦度和山体坡度,平坦度大和山体坡度缓的为Ⅰ类,反之为Ⅱ类。西太平洋的麦哲伦海山区、马绍尔群岛基本以平顶海山为主,介于中西太平洋之间的威克—马尔库斯海山区和中太平洋海山区、莱恩群岛平顶海山与尖顶海山共同发育。对各种类型海山上钴结壳分布研究发现,无论是在尖顶海山还是在平顶海山,板状结壳均比较发育,但砾状结壳在平顶海山比在尖顶海山的发育。中太平洋尖顶海山的结壳比平顶海山的发育,但由于山顶面积小,钴结壳资源量不大。仅从平顶海山看,在麦哲伦海山区、威克—马尔库斯海山区板状结壳比中太平洋海山区、马绍尔群岛、莱恩群岛的板状结壳发育,前者的板状结壳平均厚度大于3 cm,后者的板状结壳平均厚度小于3 cm,总体上是西太平洋平顶海山钴结壳比中太平洋平顶海山的发育。两种类型海山各方向上的资源分布明显不同,在平顶海山的西部山坡的资源比东部山坡的丰富,尖顶海山的则刚好相反。  相似文献   

7.
1 IntroductionCobalt-richcrust, alsoknownasferrom anganesecrustormanganesecrust, isdefined astheferroman-ganesedepositiondistributingontheseamountandoc-curringinlayer,crustandgravelornoduleinpart.Itisrich inthemetalofhigh economicvalue(cobalt,nick-el,plat…  相似文献   

8.
Seamounts and knolls are ‘undersea mountains’, the former rising more than 1000 m from the seafloor. These features provide important habitats for aquatic predators, demersal deep-sea fish and benthic invertebrates. However most seamounts have not been surveyed and their numbers and locations are not well known. Previous efforts to locate and quantify seamounts have used relatively coarse bathymetry grids. Here we use global bathymetric data at 30 arc-sec resolution to identify seamounts and knolls. We identify 33,452 seamounts and 138,412 knolls, representing the largest global set of identified seamounts and knolls to date. We compare estimated seamount numbers, locations, and depths with validation sets of seamount data from New Zealand and Azores. This comparison indicates the method we apply finds 94% of seamounts, but may overestimate seamount numbers along ridges and in areas where faulting and seafloor spreading creates highly complex topography. The seamounts and knolls identified herein are significantly geographically biased towards areas surveyed with ship-based soundings. As only 6.5% of the ocean floor has been surveyed with soundings it is likely that new seamounts will be uncovered as surveying improves. Seamount habitats constitute approximately 4.7% of the ocean floor, whilst knolls cover 16.3%. Regional distribution of these features is examined, and we find a disproportionate number of productive knolls, with a summit depth of <1.5 km, located in the Southern Ocean. Less than 2% of seamounts are within marine protected areas and the majority of these are located within exclusive economic zones with few on the High Seas. The database of seamounts and knolls resulting from this study will be a useful resource for researchers and conservation planners.  相似文献   

9.
Seamounts are habitats of considerable interest in terms of conservation and biodiversity, and in terms of fisheries for bentho-pelagic and pelagic species. Twenty previously compiled datasets including seamount/underwater feature lists, bathymetric maps and emerged feature maps from different sources (ship-derived and satellite altimetry-derived) at different spatial scales (from individual cruise to worldwide satellite data) were gathered in order to compile an enhanced list of underwater features for parts of the western and central Pacific Ocean (WCPO). The KL04 dataset [Kitchingman, A., and Lai, S., 2004. Inferences on potential seamount locations from mid-resolution bathymetric data. Fisheries Centre Research Reports 12 (5), 7–12], listing seamount positions and depths as calculated from satellite altimetry-derived bathymetry, provided the baseline data for this study as it covered the entire region of interest and included summit depth information. All KL04 potential seamounts were cross-checked with other datasets to remove any atolls and islands that had been incorrectly classified as seamounts, to add seamounts undetected by KL04, to update the overall database (geolocation, depth, elevation, and name) and to compile a 12-class typology of the different types of underwater features. Of the 4626 potential seamounts identified in KL04, 719 were multiple identifications of the same large underwater features and 373 (10%) were actually emerged banks, atolls and islands, leaving 3534 actual underwater features. Conversely, 487 underwater features were documented in other datasets but not registered by KL04. The screening of all the potential WCPO seamounts produced a final list of 4021 underwater features with agreed upon position and information. This enhanced list should have many applications in oceanography, biodiversity conservation and studies of the influence of seamounts on pelagic ecosystems and fisheries.  相似文献   

10.
The Early Cretaceous separation of Newfoundland from Iberia–Ireland is a classic example of a magma-poor continental margin with hyperextension and with widespread minor magmatism resulting in seamounts. This study defines the distribution of seamounts east of Orphan Knoll, and documents and interprets the geochemical character of the one recovered lava sample. Video imagery of lava outcrops, and the sample, were obtained by ROV from Orphan seamount, one of a linear series of small seamounts overlying transitional thinned continental crust on the seaward side of Orphan Knoll. New multibeam bathymetry and legacy seismic data show several seamounts that extend irregularly along the fault-bound NE margin of Orphan Knoll. Whole rock geochemistry shows the sample to be highly alkaline basanite or possibly tephrite. Diopside–hedenbergite, kaersutite and K-feldspar phenocrysts were analyzed by electron microprobe and scanning electron microscope, and alteration minerals including kaolinite were identified by X-ray diffraction. The highly alkaline character of the basanite is similar only to Early Cretaceous volcanic and sub-volcanic rocks erupted through thick continental crust of the Mesoproterozoic Grenville Orogeny. The location of the linear set of seamounts is related to margin-parallel faults on the seaward side of Orphan Knoll that provided a pathway for magma, although ENE-trending lineaments in individual seamounts or seamount groups suggest the influence of oceanic fracture zones. A lower gradient crest to Orphan seamount above 2,200 m suggests subaerial erosion, consistent with the presence of kaolinite as an alteration product and the absence of lava pillows at and above this depth.  相似文献   

11.
Seamounts are vulnerable ecosystems in the deep sea and can be heavily impacted by human activities, such as bottom fishing and deep-sea mining. The species composition and distribution patterns of benthic fauna is key information for the designation of marine protected areas and environmental management plans. Three contracts for cobalt-rich crust exploration have been granted to China, Japan and Korea in the Northwest Pacific Ocean by the International Seabed Authority. However, our knowledge of benthic biodiversity in this area is extremely insufficient. During 2013–2020, eight Chinese Ocean Mineral Resources R&D Association (COMRA) cruises were conducted to investigate the benthic assemblages of nine seamounts in this region. In this study, 191 ophiuroids collected from seamounts in the Northwest Pacific were identified into 29 species in 11 families. Ophiacanthidae and Euryalidae were the two most dominant families with 12 and 6 species, respectively. Ophiotomidae and Ophiopyrgidae were represented by two species each, while seven families were represented by only one species. Four species were widely distributed among 4–5 seamounts, and 17 species were found only at a single site. An integrated regional taxonomic dataset of Ophiuroidea was generated and analyzed. A total of 23 and 14 species were obtained from the Magellan Seamount Chain (MSC) and the Marcus-Wake seamounts (MWS), respectively, with 8 species shared between the two seamount groups. The individual-based rarefaction curves did not reach an asymptote, suggesting that the sampling effort was inadequate for either the entire region or each single seamount. Most species distributed in a narrow depth range, and the species composition was different between water depths above and below 2000 m. Our results greatly improve the understanding of megafaunal biodiversity from seamounts in the Northwest Pacific Ocean, and highlight the necessity of further surveys to provide more robust information for environmental protection and management in this region.  相似文献   

12.
海山可以通过与洋流的相互作用改变水体结构,促进悬浮体以及海洋生物的再分配,进而影响海洋生物地球化学过程,促进大洋物质和能量交换。西太平洋有着复杂的环流结构,也是海山分布最多的海区之一。为研究西太平洋海山区的悬浮体分布及其控制机制,2017年夏季在西太平洋卡罗琳M4海山区进行现场调查,利用扫描电镜分析了该海山区悬浮体样品的物质组成及分布,并结合温度、盐度和荧光叶绿素a浓度数据,讨论了海山对悬浮体分布的影响。结果表明,M4海山区的悬浮体由生物碎屑、矿物颗粒和絮凝体等组成。海水的强烈层化阻碍了该海山区下层营养物质的上涌,使上层水体呈现出寡营养的特征,导致大部分站位悬浮体丰度较低;但在海山顶部,潮流和海山地形相互作用在山顶上方形成反气旋环流,不仅促进了深水的营养物质向上扩散,使得荧光叶绿素a浓度升高,同时对平流输送来的以及从深水中上涌的悬浮体起到了滞留作用,使山顶上方的悬浮体丰度远高于离山顶较远的位置。随着水深的增大,温、盐跃层的强度减弱,水体中的营养盐浓度升高,为浮游生物的生长提供了适宜的环境,进而使生物碎屑及絮凝体的丰度升高。北赤道潜流挟带来自西太平洋近岸海区的陆源矿物颗粒到达M4海山区,...  相似文献   

13.
Many seamounts are covered with cobalt-rich ferromanganese crusts, and are increasingly attracting interest for the potential extraction of valuable mineral resources from deep seabed environments. However, the impacts of potential mining activities on the vulnerable seamount ecosystem remain unclear. To enhance the understanding of connectivity in benthic invertebrate populations in the Northwest Pacific, several seamounts were surveyed and biological samples collected. In the present study, the ophiuroid species Ophioplinthaca defensor is reported for the first time from four deep seamounts in the Northwest Pacific, and described, providing more detailed morphological diagnosis characters. To assess the population structure of the species between and within seamounts, two mitochondrial markers (COI and 16S) were sequenced. In total, 20 haplotypes from 32 COI sequences and 8 haplotypes from 3716S sequences were recovered. The star-shaped TCS networks and non-significant pairwise population differences reveal the absence of distinct population structures between and within seamounts. In addition, the O. defensor population seemed to have undergone a demographic expansion in history. This is the first study on the genetic population structure of a benthic invertebrate from seamounts in the Northwest Pacific, and this results suggest a potentially high, long distance dispersal capacity in O. defensor between seamounts, which could inform the development of the Regional Environmental Management Plans for the cobalt-rich crust seamounts in the area.  相似文献   

14.
During different seasons of the years 2003–2005 in the NE Atlantic, zooplankton were sampled with a MOCNESS (multiple opening/closing net and environmental sensing system, mesh size 333 μm) above the slopes and summits of Seine, Sedlo and Ampère seamounts and at remote reference sites outside the influence of the seamounts (far field). Wet weights of different zooplankton size classes (<0.5, 0.5–2, >2 cm) were measured. Night and day hauls were analysed in order to detect diel vertical migrations of the zooplankton, as well as a possible trapping effect due to the shallow topography.Biomass concentrations, independent of daytime, season and summit height, were reduced above the summits at all three seamounts compared to the slope and far-field sites. No trapping effect or retention of biomass was apparent above the seamounts. The vertical distribution patterns of the size class <0.5 cm did not differ between night and day hauls at most sites, but indications of diel vertical migrations were found in the larger size fractions. With the exception of gelatinous organisms, zooplankton >0.5 cm were nearly absent above the summits of Seine and Ampère seamounts, but considerable numbers were found above the slopes and at the far-field sites. Possible explanations for the observed distribution patterns of zooplankton biomass and size classes are discussed, including retention and lateral advection due to the hydrography at the seamounts, as well as predation by resident seamount fish.  相似文献   

15.
The Eratosthenes Seamount is a continental fragment undergoing collision with Cyprus along the African-Eurasian plate boundary. High-resolution seismic and deep-tow sonar data revealed that extensional deformation is occurring over most of the seamount, whereas compressional deformation was observed within the trench basin to the north and also in the asymmetric basin south of the seamount. This recent tectonic activity has triggered the development of slumps, turbidites and fluid escape structures. Although the 'staircase' bathymetry is similar to that of subducting oceanic seamounts, the distribution and characteristics of structures which develop during collision-subduction are very different.  相似文献   

16.
Vessel-based observations of water column structure and flow near a shallow-crested seamount are used to quantify the physical disturbance induced by that seamount. The implications of this disturbance on the ‘feeding hole’ hypothesis are then examined based on data from moored thermistors and acoustic current profilers, as well as vessel-based acoustic sounding-derived biomass estimates, currents, and conductivity-temperature-depth profiles from a 55 km square grid of stations around the crest. Mean currents in the region of 0.2 m s?1 are comparable to observations from surface drifters whereas the semidiurnal tidal flow amplitude was one third of this. Thorpe Scale-based estimates of energy dissipation rate were in the range 10?9 to 2.10?8 W kg?1 and vertical diffusivities Kz were in the range 10?4 to 10?3 m2 s?1. Turbulence levels were higher upstream of the seamount–likely due to the influence of nearby seamounts Rumble IV and V. There was no evidence of a Taylor Cap in the Rumble III velocity field. The sounder data provide some evidence of a feeding hole and analysis based on diffusivities suggests that this might persist downstream of the seamount for as much as 7 days.  相似文献   

17.
Spatial distribution patterns of zooplankton biomass in relation to local and large‐scale hydrographical and biological driving forces were studied at Ampère and Senghor, two shallow seamounts in the subtropical and tropical NE Atlantic, respectively. The study includes a first assessment of the taxonomic composition and an estimation of the respiratory carbon demand of the zooplankton community. Zooplankton was sampled during three cruises at the seamount and open ocean reference sites in May and October 2009 and in December 2010. Zooplankton standing stocks and the corresponding respiratory carbon demand were about six times higher at Senghor than at Ampère, with mean stocks of 24.7 and 4.6 g·m?2, respectively, in the upper 1000 m. Mean respiratory carbon demand in the epipelagic zone was calculated as 61.4 mg·C·m?2·day?1 for Senghor and 9.6 mg·C·m?2·day?1 for Ampère. At neither site were differences between seamount and open ocean sites significant. However, horizontal surveys across Ampère Seamount show clear differences between day and night distributions and a reduced biomass above the summit. Across Senghor, zooplankton biomass increased from the SW to the NE flank, with the highest concentrations in the subsurface layer of the chlorophyll maximum and just above a strong oxycline. The zooplankton community at Ampère Seamount reflects the oligotrophic character of the NE Atlantic subtropical gyre, whereas the nutrient‐rich waters of the cyclonic tropical gyre at Senghor support a higher biomass. This difference in the zooplankton biomass between the two seamounts can be attributed to the large‐scale hydrographical features governing the productivity regimes rather than to regional seamount effects.  相似文献   

18.
Approximately 200 seamounts of different dimensions have been identified, from multibeam bathymetry maps of the Central Indian Ocean Basin (CIOB) (9°S to 16°S and 72°E to 80°E), of which 61% form eight chains that trend N-S. The seamounts are clustered above and below 12°S latitude. Area II (9°-12°S) shows a concentration of smaller seamounts (≤400 m height), and area I (12°-15°S) has a mixed population (including both less and more than 400 m height). Inspite of the differences in their height, the seamounts of these eight chains are morphologically (slope angle, flatness, basal width) corelatable. Furthermore, we suggest that height-width ratio could be useful in identifying the style of seamount eruption. The seamount chains in the CIOB probably originated from propagative fractures and were produced between 61 and 52 Ma (chrons A26 to A23) as a result of the interaction between the conjugate crusts of the Central Indian and Southeast Indian Ridges during the Indo-Eurasian collision event.  相似文献   

19.
Approximately 200 seamounts of different dimensions have been identified, from multibeam bathymetry maps of the Central Indian Ocean Basin (CIOB) (9°S to 16°S and 72°E to 80°E), of which 61% form eight chains that trend N-S. The seamounts are clustered above and below 12°S latitude. Area II (9°–12°S) shows a concentration of smaller seamounts (≤400 m height), and area I (12°–15°S) has a mixed population (including both less and more than 400 m height). Inspite of the differences in their height, the seamounts of these eight chains are morphologically (slope angle, flatness, basal width) corelatable. Furthermore, we suggest that height-width ratio could be useful in identifying the style of seamount eruption. The seamount chains in the CIOB probably originated from propagative fractures and were produced between 61 and 52 Ma (chrons A26 to A23) as a result of the interaction between the conjugate crusts of the Central Indian and Southeast Indian Ridges during the Indo-Eurasian collision event.  相似文献   

20.
海山区浮游生态学研究   总被引：10，自引：7，他引：3  
本文综述了海山浮游生态学研究的现状。海山是大洋中常见的地形单元,在有的海山附近鱼类和底栖生物的生物量比周围大洋中要多,针对这些鱼类和底栖生物的饵料来源提出了三种假说,第一种假说认为海山区特殊的物理环境导致初级生产力较高(经典假说),第二种假说认为海山区的饵料不是本地生产的,地形和流场使得外来的浮游生物在海山区富集或通量加大(外来营养补充假说),第三种假说认为海山上部的颗粒有机物营养较高,是鱼类和底栖生物的营养来源之一(颗粒有机物补充假说)。对海山浮游生态学的研究基本围绕这几个假说进行。目前只在9座海山进行了浮游生态学研究,这些研究表明单个假说并不能解释海山附近鱼类生物量较大的现象,海山鱼类和底栖生物的营养来源可能有很多,这些假说阐述的机制并不互相矛盾,海山生物之间的营养关系也比原来想象的复杂得多。已有研究都是针对其中某个假说进行验证研究,建议我国即将进行的海山浮游生态学研究针对三种假说进行海上调查,以提供完备的数据支持。  相似文献   

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