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1.
A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9th Chinese Arctic Research Expedition (CHINARE-Arc9) in 2018 and previously published data. The new data reveal scours that developed at water depths of 850–1 030 m with an orientation of about 75°/255°. The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations, which showed a maximum scouring depth of about 900 m on the seamount. The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction. Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet. The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima. 相似文献
2.
During a recent (2006) cruise of RV ‘Dana’ high resolution side-scan sonar and sub-bottom profiling was carried out on selected shelf and slope transects offshore Disko Bugt, central West Greenland. Available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c. 1100 m water depth. The newly acquired side-scan sonar data reveal the presence of giant iceberg plow marks extending (sub)parallel to the slope between about 800 and 1085 m water depth. The height difference between bottom of the scours and rim crest is up to 40 m. The largest plow marks are about 750 m wide. To date no observed modern icebergs including those from Antarctica have drafts in excess of c. 500 m. Taking into account maximum glacial sea level lowering of c. 120 m, the paleo-iceberg keel depth was at least 950 m. Due to the presence of the relatively shallow (< 700 m) sill of Davis Strait to the south, calving of these paleo-icebergs is thought to have occurred from an ice margin in the Baffin Bay region (Jakobshavn Isbræ paleo-ice stream?). The depth of occurrence (> 1000 m) and dimensions of the plow marks are concluded to be exceptional, and comparable to glacial scouring features reported from the Arctic Ocean. 相似文献
3.
《Marine Geology》2006,225(1-4):265-278
The first seismic reflection data from the shallowest part of the submarine Lomonosov Ridge north of Arctic Canada and North Greenland comprise two parallel single channel lines (62 and 25 km long, offset 580 m) acquired from a 10 day camp on drifting sea ice. The top of southern Lomonosov Ridge is bevelled (550 m water depth) and only thin sediments (< 50 ms) cover acoustic basement. We suggest erosion of a former sediment drape over the ridge crest was either by a grounded marine ice sheet extending north from Ellesmere Island and/or deep draft icebergs. More than 1 km of sediments are present at the western entrance to the deep passage between southern Lomonosov Ridge and the Lincoln Sea continental margin. Here, the uppermost part (+ 0.3 s thick) of the section reflects increased sediment input during the Plio–Pleistocene. The underlying 0.7 s thick succession onlaps the slope of a subsiding Lomonosov Ridge. An unconformity at the base of the sedimentary section caps a series of NW–SE grabens and mark the end of tectonic extension and block faulting of an acoustic basement represented by older margin sediments possibly followed by minor block movements in a compressional regime. The unconformity may relate to termination of Late Cretaceous deformation between Lomonosov Ridge and Alpha Ridge or be equivalent to the Hauterivian break-up unconformity associated with the opening of the Amerasia Basin. A flexure in the stratigraphic succession above the unconformity is most likely related to differential compaction, although intraplate earthquakes do occur in the area. 相似文献
4.
由于海床起伏不平,斜坡的存在必然改变波浪对管线及海床的作用特性,进而影响管线三维冲刷。基于波浪港池实验,考虑规则波的作用,采用中值粒径为0.22mm的原型沙铺设与波浪传播方向成45°夹角的斜坡,研究斜向波作用下斜坡上海底管线的三维冲刷特性。通过测量管线下方冲刷坑宽度和深度的差异,分析管线三维冲刷的不均衡性。实验表明:管线的存在使斜坡上的波高有所降低;斜向波作用下管线三维冲刷的不均衡性表现为深度不均衡性和宽度不均衡性,宽度不均衡性主要是管后淤积泥沙的后移引起的,周期对三维冲刷不均衡性的影响比波高对其的影响程度大;管线自深海向近岸延展时,随水深的减小,冲刷深度分为缓慢发展阶段和快速发展阶段。 相似文献
5.
The Dongsha Basin, circling Dongsha Island that is amid the northern margin of the South China Sea, is characterized by thin (∼0.5 km) Cenozoic sediments veneering on thick (up to 5 km) Mesozoic strata. Recently, several geophysical and geological surveys, including multiple channel reflection seismic, sub-bottom profiling and benthic dredging, have been conducted on the slope southwest to the Dongsha Island, where the water depth varies from 400 m to 2000 m. A novel discovery is numerous submarine mud volcanoes of various sizes over there, typically 50–200 m high and 0.5–5 km wide. Geophysical profiles document their unusual features, e.g., roughly undulating seafloor, high-amplitude seabed reflectivity, foggy hyperbolic diffractions up to 50 m in water column above seabed, and internal reflection chaos and wipe-out down to 2–3 km level or deeper below the seabed. Benthic dredging from the mud volcanoes gives abundant faunas of high diversity, e.g., scleractinian (stony coral), gorgonian, black coral, thiophil tubeworm, glass sponge, bryozoan etc., indicating booming chemosynthetic community, among which the Lophelia pertusa-like coral and the Euretidae-like glass sponges are the first reports in the South China Sea. Concomitantly with them, there are also abundant authigenic carbonate nodules and slabs, raw, brecciated and breccias with bio-clasts congregation. Besides, there coexist massive mudflows and allogenic coarse-grained quartz, feldspar and tourmaline most likely brought out by mud volcanism. Geochemical analysis of the bottom water samples give dissolved methane concentration up to 4 times higher than the background average. These results lend comprehensive evidences for the ongoing and historical mud volcanism. The escaping methane gas is inferred to source mainly from the Mesozoic strata. Occupying a large province of the deep water slope, ca. 1000 km2 or more, the mud volcanoes is prospective for gas hydrate and natural gas for the Dongsha Basin. 相似文献
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7.
Riko Noormets Verner B. Ernstsen Alex Bartholomä Burg W. Flemming Dierk Hebbeln 《Geo-Marine Letters》2006,26(3):165-176
The bedforms and the local scour at the base of a cylindrical pile were studied in a tidal inlet in the Wadden Sea, southern North Sea, using high-resolution multibeam bathymetry data from four surveys. The observed changes in scour and bedform dimensions were interpreted in terms of hydraulic forcings varying periodically at different time scales. It appears that bedform orientation reacts to changing flow conditions on a semidiurnal basis, whereas bedform height and steepness reflect the spring-neap cycle as well as seasonal signals. The scour depth carries a strong overprint of the semidiurnal tidal cycle, which is at a maximum during the strongest tidal flow. Subtler variations in scour depth can possibly be attributed to the spring-neap tidal cycle. Based on these data on bedform and scour dimensions, correlation functions were established between scour depth and dune height as well as dune length. In measuring the scour depth under mobile bed conditions, establishing the seabed level based on the trough level of the bedforms nearest to the scour proved useful. These findings suggest that the dimensions of bedforms in dynamic equilibrium with prevailing hydraulic flow conditions can be used to estimate scouring in tidal environments. 相似文献
8.
海床冲淤变化对港口与航道工程建设非常重要。由于泥沙供给、人类活动和其他等因素的影响，海床冲淤变化非常复杂。洋山深水港是一个新兴的深水港口，是上海国际航运中心重要的组成部分，它的建设引起了各方的广泛关注。目前，洋山水深港一、二、三期港区在潮流运动和定期疏浚下保持着良好的水深。四期港区工程是世界上最大的全自动化深水码头，2017年12月以开港运行。本论文基于大量的地形资料、水文泥沙资料，分析了整个洋山深水港多年来的海床冲淤变化和近期四期工程海域海床冲淤变化。结果显示：1998-2010年整个洋山港区海床冲淤变化表现为较大幅度的冲淤，在洋山主通道内呈现为"南淤北冲"的格局，但是颗珠山汊道一直以来均表现冲刷的趋势；四期港区水域近一些年来也表现为一个冲刷的趋势，多年年均冲刷幅度0.7m左右；讨论了外界泥沙供给、港口工程陆域边界封堵、港池疏浚和由此带来的水流的变化以及泥沙水力特性等因素的对洋山港海域海床冲淤变化的影响，在众多因素中，颗珠山汊道的存在（或保留）对洋山西部水域或四期港区水域冲刷有着积极的作用，它的存在所产生的落潮作用对四期港区的水深维护起到重要的正面影响。 相似文献
9.
Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean 总被引：3，自引：0，他引：3
Graldine Sarthou Alex R. Baker Jurjen Kramer Patrick Laan Agathe Laës Simon Ussher Eric P. Achterberg Hein J.W. de Baar Klaas R. Timmermans Stphane Blain 《Marine Chemistry》2007,104(3-4):186-202
Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters. 相似文献
10.
Francis Freire Richard Gyllencreutz Rooh Ullah Jafri Martin Jakobsson 《Geo-Marine Letters》2014,34(4):315-325
The western Svalbard continental margin contains thick sediment sequences with areas known to contain gas hydrates. Together with a dynamic tectonic environment, this makes the region prone to submarine slides. This paper presents results from geophysical mapping of the deepest part of the high Arctic environment, the Molloy Hole. The mapping includes multibeam bathymetry, acoustic backscatter and sub-bottom profiling. The geophysical data reveal seabed features indicative of sediment transport and larger-scale mass wasting. The large slide scar is here referred to as the Molloy Slide. It is located adjacent to the prominent Molloy Hole and Ridge system. The slide is estimated to have transported >65 km3 of sediments over the deep axial valley of the Molloy Ridge, and further into the Molloy Hole. A unique feature of this slide is that, although its run-out distance is relatively short (<5 km), it extends over an enormous vertical depth (>2,000 m) as a result of its position in a complex bathymetric setting. The slide was most likely triggered by seismic activity caused by seafloor spreading processes along the adjacent Molloy Ridge. However, gas-hydrate destabilization may also have played a role in the ensuing slide event. 相似文献
11.
Aggeliki Georgiopoulou Russell B. Wynn Douglas G. Masson Michael Frenz 《Marine and Petroleum Geology》2009,26(10):2021-2031
The northwest African margin has been affected by numerous large-scale landslides during the late Quaternary. This study focuses on a recent collapse of the Sahara Slide headwall and characterises the resulting flow deposit. Core and seismic data from the base of the upper headwall reveal the presence of blocky slide debris, comprising heavily deformed hemipelagic slope sediments. The blocky slide debris spilled over a lower headwall 60 km downslope and formed a thick transparent debris flow unit. Cores recovered 200–250 km farther downslope contain a surficial turbidite that is interpreted to be linked to the headwall collapse event based on timing and composition. One core located approximately 200 km from the headwall scar (C13) contains debrite encased in turbidite. The debrite comprises sheared and contorted hemipelagic mudstone clasts similar as those seen in the vicinity of the Sahara Slide headwall, and lacks matrix. This debrite pinches out laterally within 25 km of C13, whereas the accompanying turbidite can be correlated across 700 km of the northwest African margin. The linked turbidite–debrite bed is interpreted to have formed through recent failure of the steep Sahara Slide headwall that either 1) generated both a debris flow and a turbidity current almost simultaneously, or 2) generated a debris flow which with entrainment of water and progressive dilution led to formation of an accompanying turbidity current. 相似文献
12.
The East Sea, with an average depth of 1700 m, has long been subject to heavy fishing pressure, resulting in derelict fishing gear. Most derelict fishing gears, such as fishing nets, fishing ropes, and crab pots, sink to the seabed and do not degrade. This gear results in “ghost fishing,” which has adverse impacts on deep benthic habitats. Recently, the Korean government has started to remove derelict fishing gears from the deep seabed of the East Sea by bottom trawling with heavy hooks (50–80 kg) and ropes. A total of 207.8 and 252.2 tons of marine debris in 2009 and 2010, respectively, were removed from the seabed, most of which were derelict fishing gears. Contrary to monitoring surveys and clean-up in shallow waters, removal of marine debris from remote deep habitats is much more difficult and dangerous for removal crews. 相似文献
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14.
We present several types of data which show that strong geostrophic bottom currents are present in a broad valley in the deep western Bay of Bengal adjacent to the Indian margin. Sea-floor photographs show well-developed current lineations with scour marks on the northern sides and sediment deposition tails on the southern sides of some objects (such as fecal pellets) suggesting strong southward-flowing bottom currents. A direct current measurement made in the region confirms this inferred flow direction. The nepheloid layer is much stronger in the western Bay of Bengal than in any other region of the northern Indian Ocean and indicates strong turbulence and a high concentration of suspended sediment at or near the sea floor. Additional data which do not provide unequivocal evidence for, but may also be indicative of, the existence of the bottom currents are as follows: the dispersal of the peninsular Indian rivers-derived smectite-rich sediments all along the valley to as far as south of Sri Lanka; a zone of sediment waves (as recorded on 3.5-kHz echograms) parallel to the regional trend of bathymetric contours along the Indian margin; and the frequent occurrence of thin, sharp and uniform layers of fine sand and silt beds rather than thick graded turbidite beds in the cores from the broad valley in the deep western Bay of Bengal. 相似文献
15.
Nikolaos Kontopoulos Teresa Fokianou Abraham Zelilidis Christos Alexiadis Nikolaos Rigakis 《Marine and Petroleum Geology》1999,16(8):223
Two depocentres, >4200 m and >3200 m thick, have been recognized in the Mesohellenic piggy-back basin of middle Eocene to middle Miocene age, where submarine fans have accumulated unconformably over an ophiolite complex. The hydrocarbon potential is indicated by the presence of kerogen types II/III with minor amounts of type I; the evidence is mostly for wet gas and gas, with minor oil. Source rocks are the middle Eocene to lower Oligocene Krania and Eptachori formations, of up to 2000 m total thickness, reaching maturation during the early Miocene. The source rocks consist of outer fan and basin plain deposits. They are conformably overlain by the lower member (late Oligocene) of the up to 2600 m thick Pentalophos Formation, which consists mostly of thick submarine sandstone lobes. Possible stratigraphically trapped reservoirs include the lower member of the Pentalophos Formation, which overlies source rocks, as well as limestones tectonically intercalated within the ophiolite complex, underlying the source rocks. Traps may have formed also on the western side of an internal thrust (Theotokos Thrust), which influenced the evolution of the depocentres. 相似文献
16.
Shelf break systems are highly dynamic environments. However little is known about the influence that benthic interactions and water mass mixing may have on vertical distributions of iron in these systems. Dissolved Fe (< 0.4 μm) concentrations were measured in samples from nine vertical profiles across the upper slope (150–2950 m water depth) at the Atlantic Ocean–Celtic Sea shelf break. Dissolved iron concentrations varied between less than 0.2 and 5.4 nM, and the resulting detailed section showed evidence of a range of processes influencing the Fe distributions. The near sea floor data were interpreted in terms of release and removal processes. The concentrations of dissolved Fe present in near seabed waters were consistent with release of Fe from in situ remineralisation of particulate organic matter at two upper slope stations, and possibly release from pore water upon resuspension on shelf. Lateral transport of dissolved iron was evident from elevated Fe concentrations in an intermediate nepheloid layer and its advection along isopycnals. Surface waters at the shelf break also showed evidence of vertical mixing of deeper iron-rich waters. These waters contained macronutrients that sustained primary productivity in these otherwise nutrient-depleted surface waters. The data also suggest some degree of stabilisation of relatively high concentrations of iron, presumably through ligand association or as colloids. This study supports the view that lateral export of dissolved iron to the interior of the ocean from shelf and coastal zones and may have important implications for the global budget of oceanic iron. 相似文献
17.
舟山册子岛-镇海段海底原油管道连续多年监测数据显示,局部海床冲刷较为严重,管道多处裸露、悬空,对工程安全构成威胁。基于Delft3D建立杭州湾口二维水流泥沙数学模型,并利用实测潮位、流速、流向及悬沙质量浓度资料对模型进行率定与验证,进而模拟分析近年来人为开发活动对海底管道附近海床冲淤变化的影响。分析结果表明,新泓口围垦工程和金塘大桥工程对管线镇海登陆段海床冲刷影响较大,金塘大桥桥墩阻水作用加剧了管线深槽边坡西半段海床的冲刷,另外管线深潭延伸东半段的海床冲刷与金塘大桥主通航孔密切相关。 相似文献
18.
根据路由勘察区水深测量、旁侧声纳、浅地层剖面探测等多项物理探测所获取的资料，结合其它自然环境及历史资料，对勘察区内海底工程地质条件进行了详尽的分析和研究．此外，还对近20a来勘察区海床稳定性进行初步分析，为选择一条最佳的路由通道提供依据．研究分析表明：可能影响该海缆安全运行的不良工程地质条件主要为海底灾害性地貌，如基岩、潮流冲刷槽等；勘察区不同区域内海底冲淤变化存在一定差异，潮汐通道底部受较强冲刷，冲刷速率为0．035～0．1m／a，20m以浅区域海底处于弱冲刷状态一冲淤动态平衡状态，冲刷速率为0．015m／a，海床较稳定；该路由勘察区工程环境较适合海缆的铺设，且其最佳路由区域是在勘察区南半部相对稳定的海底平滑区． 相似文献
19.
This paper re-examines the Upper Miocene Upper Mount Messenger Formation, Taranaki Basin, to characterize its architecture and interpret its environmental evolution. Analysis of stratal architecture, lithofacies distributions, and paleotransport directions over the 250 m thick formation shows the outcrops provide a nearly dip parallel section displaying the lateral relationships between contemporaneous channel-levee and overbank depositional environments. At least five 30–40 m thick upward fining units are recognized in the north-central parts of the outcrop and are interpreted as large-scale overbank avulsion cycles. Each unit consists of thick- to medium-bedded predominantly planar laminated sandstone turbidites at the base that fine upward into thin- to very thin-bedded, planar laminated and ripple cross-laminated mud-rich turbidites. The units are traceable laterally over a distance exceeding 3 km where they are cut by channels that show basal mudstone draped by medium- to thin-bedded sandstone, and onlapped by thick-bedded planar laminated sandstone at the margin. The channels are separated by tapered packages of medium- to thin-bedded turbidites containing climbing-ripple cross-lamination interpreted as levees. The individual channel-levee and overbank avulsion cycles formed through four stages: 1) a channel avulsion spread sand into the overbank as an unconfined splay, 2) preferential scouring in one area of the splay led to development of a channel with small levees that prograded across the splay, 3) a deep incision followed by abandonment of the channel deposited a mud lining. Alternatively, the mud lining was formed during the first stage as the downdip portion of the channel was abandoned. 4) The channel filled at first by thick-bedded planar laminated and then by climbing-ripple cross-laminated sand. At this time, the growth of constructional levees progressively limited sand into the overbank. Ratios of Bouma division thicknesses calculated over a stratigraphic interval present a new method to distinguish deep-water depositional environments. 相似文献
20.
基于水槽实验,研究植物对孤立波作用下直立堤局部冲刷的影响。通过改变实验入射波高、植物带的宽度和密度,分析各要素对直立堤局部冲刷的影响。实验对波高沿程变化、孤立波越堤、回落过程以及地形演变进行全程的测量和记录,并进行有无植物带保护的直立堤局部冲刷对比分析。结果表明,植物带的存在,使得堤后相对最大冲刷深度显著减小,堤前冲刷形态由单峰式"L"型变为双峰式淤积沙坝形态,且冲刷位置由原堤脚前移至植物带所在位置,冲刷范围大幅增加。减小植物带密度或者植物带宽度会使近岸侧或是离岸侧的相对最大冲刷深度和相对最大淤积高度有增大的趋势,但是当入射波高增大时,二者的影响不显著。该研究对实际工程中植物带的合理布置提出了具有参考性的建议,对减少堤防工程的冲刷和损失有一定现实意义。 相似文献