A Late Pleistocene submarine slide on the Bear Island Trough Mouth Fan

A large submarine slide on the southern flank of the Bear Island Trough Mouth Fan, southwestern Barents Sea continental slope, has a run-out distance of about 400 km, a total volume of about 1100 km³, and is younger than 330 ka. Three seismic units, comprising mainly hemipelagic sediments has partly filled the slide scar. An increased sedimentation rate on the Bear Island Trough Mouth Fan from Late Pliocene time, probably in combination with abundant earthquakes, is the most likely cause of the slide. Based on these and previous studies, we suggest that large-scale slides were important sediment transport processes during Plio-Pleistocene.     

Spatial distribution of sister species of vesicomyid bivalves Calyptogena okutanii and Calyptogena soyoae along an environmental gradient in chemosynthetic biological communities in Japan

Vesicomyid bivalves have a substantial biomass in deep-sea chemosynthetic biological communities in the Pacific. Using a novel multiplex-PCR (mPCR) method to identify the co-occurring vesicomyids in Sagami Bay, we analyzed the distribution of Calyptogena okutanii and Calyptogena soyoae along environmental gradients. All the known distributions of C. okutanii indicated the different preferences in salinity and temperature to those of C. soyoae, and in Sagami Bay, depth seemed to be an important environmental factor, too. Although the concentration of hydrogen sulfide in sediment was not examined, our results showed that the distributions of these two Calyptogena clams were affected by salinity and temperature.     

The effects of variable speeds of a submarine block slide on near-field tsunami amplitudes

In this study, the motion of a submarine block slide, with variable velocities, and its effects on the near-field tsunami amplitudes are investigated. The numerical results show that the amplitudes generated by the slide are almost the same as those created by its average velocity when , where is average velocity of the slide and is the long period tsunami velocity in ocean of constant depth h. In contrast, the kinematic model of the slide must take into account time variations in the moving velocity, if , especially when .     

The Brunei slide: A giant submarine landslide on the North West Borneo Margin revealed by 3D seismic data

Three dimensional seismic data, offshore Brunei, provide evidence for a giant landslide with a volume of 1200 km³, an area of ∼ 5300 km² and an average thickness of ∼ 240 m. It extends for over 120 km from the Baram Canyon in ∼ 200 m water depth to the deep basin floor of the North West Borneo Trough. The landslide is a unique example of a major submarine landslide located on a steep, tectonically active margin adjacent to a large river and canyon system. The landslide is mappable using 3D seismic data, which allow detailed imaging of internal flow structures, erosional headwall and the basal sliding surface. The landslide is a complex deposit, involving a chaotic debris flow matrix, with flow structures and blocks 500 to 1000 m wide and up to 250 m thick. Imaging of the basal sliding surface reveals large striations ∼ 30-120 km long, ∼ 100-600 m wide, and ∼ 10-30 m deep that show significant amounts of basal erosion. In the landslide source area we describe fluid escape structures, gas buildups and bottom simulating reflectors, which may provide a mechanism for weakening and triggering slope failure. We also report older landslides, buried several hundred meters beneath the basin floor that indicate giant landsliding is a recurrent process in the NW Borneo Trough.     

Geotechnical properties of a submarine slide area on the U.S. continental slope northeast of Wilmington canyon

Abstract

A relatively large submarine slide (slump block) and apparent unstable surficial sediments undergoing creep have been delineated in bathymetric and seismic reflection profiles along the U.S. Atlantic continental margin northeast of Wilmington Canyon. A downslope core transect was made over selected areas to assess the geotechnical properties of the sediments associated with the slide. Sediments are predominantly silty clays and clayey silts rich in illite, with lesser quantities of feldspar, kaolinite, chlorite, quartz, and smectite minerals. Surficial sediments (cored up to 12 m) upslope from the slump block reveal typical variations in the mass physical properties with core depth. Shear strength and wet unit weight show a steady increase with depth below the mudline commensurate with a decrease in water content. In contrast, surficial sediments downslope overlying the slump block generally have low shear strength and relatively high variability in other mass physical properties with core depth. Chemical evidence of slumping (as defined by the sulfate ion content) is not apparent in the pore waters collected from the upper 10 m of sediment. No important relationships are obvious among the physical and chemical properties, specifically the carbonates or complex solids of iron and manganese oxides or hydroxides. Sediment failure in the form of a major submarine slide appears to have been a significant deformational process during the geological past (late Pleistocene). Creep and associated deformational features recorded in the surficial sediments are presumably a result of recent geological processes.     

Physical,biological, geochemical and sedimentological controls on the ichnology of submarine canyon and slope channel systems

Sediments of the continental slope are commonly bioturbated by endo- and epibenthic organisms, particularly in and around submarine canyons and channels. This study reviews the architecture and depositional environments associated with canyons and channels on the continental slope, and assesses the key physical and chemical conditions encountered in and around these conduits. Hydrodynamic energy, concentration and quality of organic carbon, dissolved oxygen concentration and sedimentation rate are identified as key controls on the composition of benthic ecosystems in slope environments. Submarine canyons and channels focus a variety of turbid and clear-water currents, all of which serve to increase the concentration of oxygen, labile organic carbon and other nutrients, which tend to elevate the abundance and biodiversity in the seafloor sediments, compared with those of the surrounding slope. Ancient slope channel and canyon systems reflect some of the variation in ichnological assemblages that is seen in modern analogues, although processes of erosion and trace fossil preservation mean that the benthic environment is often incompletely preserved in the ancient record. By integrating current understanding of sedimentology, oceanography, biology and ichnology of slope environments it is possible to provide a first order summary of the inter-relationships between ichnology and depositional environments on the continental slope. The combination of these data has the potential to improve our understanding of changes in deep marine benthic ecosystems through geological time, and to further the use of ichnology in assessing hydrocarbon reservoir presence, quality and performance from bioturbated slope, canyon and channel-levee hydrocarbon reservoirs.     

渔业活动对东海海域海底光缆安全的影响

通过对东海海域海底光缆路由区作业渔场的捕捞方式、作业范围等的分析,结合已建海底光缆故障的调查结果,探讨了渔业活动对东海海域海底光缆路由调查和已建海底光缆安全的影响。结果表明,东海海域海底光缆主要穿越了长江口、江外、舟山、舟外、鱼外等5大主要作业渔场,各渔场的渔业活动频繁,拖网、张网和流刺网等不同捕捞作业方式集中,对海底光缆的安全带来严重威胁。同时,捕捞渔船船只的数量逐年增多、触底深度的不断增加、作业时间的不断延长,使海底光缆路由调查时所获得调查资料的质量受到严重影响,船只、渔具的日益大型化以及拖网、张网、围网等捕捞活动范围的持续扩大,更使得海底光缆的故障频繁发生。为保护海缆的安全,在目前的经济技术条件下,建议选择休渔期时进行路由调查,在捕捞活动的频繁区,选择双层铠装型(DA)的海底光缆,并适当加大埋设深度,以降低渔业活动对海底光缆工程的影响。实践表明,将海底光缆埋设深度增加至3.0 m以上,可有效地保护海底光缆的安全。     

用数值计算方法分析潜艇计程仪测速误差

介绍潜艇水压式计程仪的使用原理和方法,分别对SUBOFF潜艇在水面和水下两种航行状态进行了三维粘性数值模拟,获得潜艇计程仪相关部位的流场信息,利用这些信息仿效计程仪的测速过程,得出潜艇水压式计程仪"水上标定,水下用"将会使潜艇测速结果低于实际航速的结论.     

Hydro-acoustic remote sensing of benthic biological communities on the shallow South East Australian continental shelf

Information regarding the composition and extent of benthic habitats on the South East Australian continental shelf is limited. In this habitat mapping study, multibeam echosounder (MBES) data are integrated with precisely geo-referenced video ground-truth data to quantify benthic biotic communities at Cape Nelson, Victoria, Australia. Using an automated decision tree classification approach, 5 representative biotic groups defined from video analysis were related to hydro-acoustically derived variables in the Cape Nelson survey area. Using a combination of multibeam bathymetry, backscatter and derivative products produced highest overall accuracy (87%) and kappa statistic (0.83). This study demonstrates that decision tree classifiers are capable of integrating variable data types for mapping distributions of benthic biological assemblages, which are important in maintaining biodiversity and other system services in the marine environment.     

Numerical analysis of the impact forces exerted by submarine landslides on pipelines

Submarine pipelines that transport crude oil and natural gas are often in a complex marine geological environment and may become unstable and fail upon impact by submarine landslides. Previous research has mostly focused on the impact forces exerted by submarine landslides on suspended pipelines, but the impact of submarine landslides on pipelines laid on the seafloor at various impact angles, θ, have been relatively infrequently discussed, and the effects of suspended height, H, on the impact forces exerted by submarine landslides on pipelines have not been thoroughly investigated. In this study, based on the Herschel–Bulkley model, the impact forces exerted by a submarine landslide on laid-on or suspended pipelines at various impact angles θ were simulated using the computational fluid dynamics (CFD) approach. Equations for calculating the axial and normal drag coefficients of a submarine pipeline were proposed. The CFD numerical simulation results were rearranged based on the soil mechanics approach. By comparing the parameters, an essentially corresponding relationship was found between the soil mechanics and CFD approaches when the equations were used to calculate the impact forces exerted by a submarine landslide on a pipeline. In addition, a semi-analytical expression for the failure envelope was provided. Furthermore, the effects of H on the forces on a pipeline were discussed, and an equation for calculating the acting forces on a pipeline along the flow direction of a submarine landslide that comprehensively accounts for the effects of θ and H was proposed. The lift force was discussed preliminarily and the results provide a basis for further investigation. The achievement of this study is applicable for selecting locations of submarine pipeline routes and for designing submarine pipelines.     

基于LS-DYNA海底悬空管道受坠物碰撞动力响应分析

基于ANSYS/LS-DYNA动力学分析软件,采用非线性动力有限元法,对坠物撞击海底管道的过程进行数值仿真。通过大量的数值模拟得出:相同坠落物能量的情况下,悬空管道的凹陷损伤深度与裸露管道的相比偏小,且随着坠落物能量的增加,其差值增大;随着坠落物速度、坠落物质量的增大,管道撞击部位凹陷变形加剧,海底管道悬空段的最大振动幅值增大;相同坠落物能量的情况下,坠落物与悬空管道的接触面积越小,悬空管道的损伤深度越大;海床土体参数(剪切弹性模量、内摩擦角、密度)的变化对悬空管道的凹陷损伤深度及悬空段的最大振动幅值的影响较小。     

海底管道受坠物锚击损伤试验与数值模拟研究

为探索海底管道在锚击作用下的损伤规律,通过海底管道损伤试验和数值模拟,研究了坠物质量、坠落高度和坠物形状对海底管道机械损伤的影响,并结合试验结果修正了Ellinas-Wallker公式。研究结果表明:管道的凹陷损伤随坠物质量和坠落高度的增大而变大;在相同质量的立方体、球体和模型锚三种形状坠物作用下,球体坠物对管道的损伤最严重;EllinasWallker公式计算结果偏于保守,修正后计算结果与试验和数值模拟结果吻合良好。研究结果可以为海底管道的工程设计及应用提供一定的参考。     

The influence of physical and biological processes on the ichthyoplankton communities in the Gulf of Sirte (Southern Mediterranean Sea)

This paper reports on the first study on the ichthyoplankton community structure in the Gulf of Sirte and its spatial distribution in relation to environmental conditions and zooplankton abundance. The results make an important contribution to the future management of fisheries in this unexplored, but much exploited, area. Biological samples were collected in July 2008 using a Bongo40 net. In total, 1914 larvae were found and 1652 of these were identified. In particular, bathypelagic taxa were the most abundant, followed by demersal, mesopelagic, pelagic and epipelagic taxa. The ichthyoplankton community had a patchwork distribution influenced by oligotrophic conditions, the bottom depth and oceanographical features. The results suggest that environmental forcings were able to transport the ichthyoplankton to productive areas. Indeed, maximum fish egg densities were found in coastal stations in correspondence with the Atlantic Tunisian Current inflow, whereas larvae were mainly concentrated in the east side of the Gulf, probably as a result of advection by the anticyclonic circulation. Additionally, the distribution patterns of the total larvae density and the different assemblages were well matched with the abundance of the zooplankton, probably determining final larval survival, growth and recruitment.     

Disturbance caused by freshwater releases of different magnitude on the aquatic macroinvertebrate communities of two coastal lagoons

The response of the aquatic macroinvertebrate communities to freshwater releases of different magnitude and persistence was investigated in two Mediterranean coastal lagoons (Ca l’Arana and Ricarda). The study was carried out during 14 months (June 2004–July 2005) in which different environmental variables and the macroinvertebrate communities associated with two different habitats, the Phragmites australis belt and the deep area of the lagoons, were sampled monthly. Additionally, potential colonizing sources were identified through the analysis of Chironomidae pupal exuviae. The initial response of the communities to the freshwater releases was similar, being characterized by a peak of opportunistic taxa (mainly Naididae), but the late response was different for each lagoon. In the Ca l’Arana, the magnitude of the freshwater release was higher (salinity dropped below five, which is the limit commonly established for most freshwater species) and its persistence was also higher, allowing the colonization of the lagoon by new insect taxa, which replaced the brackish water species. In the Ricarda, the salinity never dropped beyond five and pre-disturbance conditions were rapidly re-established. This, together with the acclimatizing mechanisms showed by the species Chironomus riparius and Hediste diversicolor, permitted the recovery of the pre-disturbance macroinvertebrate community.     

Contrasting patterns in the abundance of fish communities targeted by fishers on two coral reefs in southern Mozambique

Coastal populations of maritime countries in eastern Africa rely on fish as a primary source of protein, but baseline information on the abundance of fish communities on these coastlines is often lacking. We used baited remote underwater video stations to compare the abundance and diversity of reef fishes targeted by fishing at two sites in southern Mozambique, one at Lighthouse Reef within the Bazaruto Archipelago National Park and the other to the south at San Sebastian Reef on the San Sebastian Peninsula. Fish that are known targets of fisheries (mostly small-scale and artisanal) had an abundance that was almost three-times greater at San Sebastian Reef (80.22 ind. h^–1 [SE 18.00]) than at Lighthouse Reef (29.70 ind. h^–1 [SE 8.91]). Similarly, there was greater mean species richness at San Sebastian Reef (38.74 species h^–1 [SE 2.79]) than at Lighthouse Reef (25.37 species h^–1 [SE 3.66]). The main drivers of targeted fish abundance were habitat and depth, with shallow (<15 m) and mixed reef areas having the greatest abundance and richness. More sampling was done over sand habitat at Lighthouse Reef, which likely led to the lower abundance and species richness observed at this site; however, that finding could also be attributable to the fact that protection is provided to only a section of available coral reef habitat in a small area. Nevertheless, fish community structure was comparable between the sites, with similar proportions of carnivores (78–81%), herbivores (12–14%) and omnivores (7–8%). Our findings highlight the variation in species abundance and assemblages of coral-reef fish targeted by fishing in Mozambique and emphasise the importance of localised environmental variables as a driver of these patterns. To ensure maximum protection of Lighthouse Reef fish communities, we recommend an extension of the no-take zone to include the entire reef complex.     

Effects of Listriolobus pelodes (Echiura) on coastal shelf benthic communities and sediments modified by a major California wastewater discharge

The Palos Verdes coastal zone off Los Angeles receives over 1·4×10⁹ l of primary treated wastewaters daily. Benthic effects from this discharge include elevated organic matter and trace contaminants in sediments, generation of H₂S among sediment porewaters and altered biological community structure. In 1973 large numbers of the echiuran Listriolobus pelodes settled in shelf sediments several kilometers from the outfalls. By 1975 the centre of Listriolobus distribution had shifted towards the outfall region, where peak numbers (1500 m⁻²) and biomass (2 kg m⁻²) developed. Populations declined in 1977 and the echiuran had virtually disappeared from the shelf by 1978. The echiurans' burrowing, respiratory, and feeding activities aerated and reworked sediments, and thus reduced wastewater impacts on the ocean bottom, enabling a diverse fauna to develop in the outfall region. With the disappearance of the echiuran, sediment quality and benthic communities reverted towards former conditions. However, because of improvements made in effluent quality during the echiuran period, wastewater impacts were of lower magnitude than before the Listriolobus invasion.     

Hemipelagic deposits on the Mendeleev and northwestern Alpha submarine Ridges in the Arctic Ocean: acoustic stratigraphy,depositional environment and an inter-ridge correlation calibrated by the ACEX results

The first high resolution multichannel seismic data from the Mendeleev and Alpha Ridges in the Arctic Ocean have been used to investigate the depositional history, and compare acoustic stratigraphies of the three main sub-marine ridges (Mendeleev, Alpha and Lomonosov) in the polar ocean. Acoustic basement on the Mendeleev Ridge is covered by a ~0.6–0.8 s thick sediment drape over highs and up to 1.8 s within grabens. A pronounced angular discordance at 0.18–0.23 s below the seafloor along the middle to upper slopes divides the succession into an upper, undisturbed, uniformly thick, hemipelagic drape (Unit M1) and a partially truncated lower unit (Unit M2) characterized by strong reflection bands. Unit M2 is thicker in intra-ridge grabens and includes three sub-units with abundant debris flows in the uppermost subunit (M2a). The discordance between Units M1 and M2 most likely relates to instability along the middle to upper slopes and mass wasting, triggered by tectonic activity. The scars were further smoothed by bottom current erosion. We observe comparable acoustic stratigraphy and discordant relationships on the investigated northwestern part of Alpha Ridge. Similarly, on the central Lomonosov Ridge, Paleocene and younger sediments sampled by scientific drilling include an uppermost ~0.2 s thick drape overlying, highly reflective deposits with an angular unconformity confined to the upper slope on both sides of the ridge. Sediment instability on the three main ridges was most likely generated by a brief phase of tectonic activity (~14.5–22 Ma), coinciding with enhanced bottom circulation. These events are coeval with the initial opening of the Fram Strait. The age of the oldest sediments above acoustic basement on the Mendeleev- and west-central Alpha Ridges is estimated to be 70–75 Ma.     

紫菜纳豆菌发酵物中醇提物和多糖生物活性的初步研究

纳豆菌(Bacillus natto)发酵后的条斑紫菜经稀释、离心后上清液用一定浓度的乙醇处理获得醇沉物和醇溶液。将醇沉物去蛋白得到粗多糖,进行抗氧化活性的研究;将醇溶液旋转蒸发得到浸膏,将浸膏按极性大小分相萃取分别得到石油醚相、乙酸乙酯相和正丁醇相浸膏,探讨分相浸膏对金黄色葡萄球菌、枯草芽孢杆菌、四联微球菌的抑菌效果。通过测定多糖和分相浸膏对羟自由基(·OH)和DPPH自由基的清除能力评价其抗氧化能力。结果表明:醇溶物对金黄色葡萄球菌具有抑制作用,且随着浓度的升高各相浸膏对羟基自由基的清除率随之升高,其中,正丁醇相浸膏在质量浓度为0.5 mg/m L时对羟自由基的清除率达到91.6%,说明条斑紫菜经纳豆菌发酵可能产生了活性化合物;与对照组相比,利用纳豆菌发酵紫菜发酵物中多糖提取率增加了0.24%,发酵得到的多糖在质量浓度为5.0 mg/m L时对羟自由基的清除率达到了95.7%。