Non-destructive porosity determinations of antarctic marine sediments derived from resistivity measurements with an inductive method     

S. Gerland  M. Richter  H. Villinger  G. Kuhn 《Marine Geophysical Researches》1993,15(3):201-218

The fractional porosity of marine sediments is one of the fundamental index properties of rocks. For the determination of porosity a nondestructive, inductive method was used on unsplit sediment cores. The results were compared with galvanically measured resistivities using a miniature Wenner array on split cores. The measurements agree well except for cores with high clay content where measurement frequency related effects cause a resistivity difference of about 10%. Porosities were derived from resistivities using a published resistivity-porosity relationship by Boyce (1968) and compared with sample porosities. A comparison of both data sets shows good agreement.  相似文献   

Impact of small-scale biogenic sediment structures on bacterial distribution and activity in Arctic deep-sea sediments   总被引：1，自引：0，他引：1  

Nadia V. Quéric  & Thomas Soltwedel 《Marine Ecology》2007,28(S1):66-74

  相似文献   

Experiments on the resuspension of estuarine sediments containing benthic diatoms     

V. N. de Jonge  J. van den Bergs 《Estuarine, Coastal and Shelf Science》1987,24(6)

A laboratory system was used to test the effect of water flow on the resuspension of mud and sand sediments and, specifically, benthic diatoms from the Ems estuary, The Netherlands. Current velocities generated by two rotating cylinders in a cylindrical tank were determined by a small float and a laser Doppler velocimeter. At low angular velocities, the amount of suspended matter increased linearly with angular velocity and the float current velocity. However, at higher angular velocities, the increase in current velocity was less because of the strong turbulence: concomitantly, the current velocity boundary layer (δ) became thinner and the suspended matter concentration increased rapidly. The dominant diatom species from the sandy sediment were suspended in two distinct groups, one of which consisted of the species Navicula aequorea, Navicula salinicola, Ophephora martyi and Opephora pacifica, and was more exclusively bound to sand grains than the other. The benthic diatom species inhabiting the silty sediment did not show this difference. The most important shortcoming in the experiments was the inability to determine the radial and vertical velocity components. This precluded reliable calculations of the shear stress. The data presented emphasize the importance of finding a method to determine the shear stress under experiments and field conditions so that direct comparisons can be made. Despite this it is assumed that, just as under the experimental conditions discussed, under natural conditions in shallow waters resuspension starts at current velocities as low as ca. 10 cm s⁻¹.  相似文献   

Expulsion of Shallow Gas in the Skagerrak—Evidence from Sub-bottom Profiling, Seismic, Hydroacoustical and Geochemical Data     

P. Hempel  V. Spieß  R. Schreiber 《Estuarine, Coastal and Shelf Science》1994,38(6)

A combined high resolution seismic, sub-bottom profiling, and multi-beam echo-sounding survey in the Skagerrak (Danish sector of the North Sea) together with gas analyses at a station along the profile exhibit the expulsion of gas (mainly methane) and the presence of gas-charged sediments at shallow depth. The echo-soundings yield detailed insight into the distribution and shape of typical sea-floor features associated with gas seepage, such as pockmarks. The pockmarks reach dimensions of 800 m in length, 300 m in width, and 15 m in depth, with the long axis running parallel to the slope of the Norwegian Trench. Processing of the multi-channel high resolution seismic data and the digitally recorded sub-bottom profiler signals indicate an internal compressional velocity of about 1050 m s^-1 within the gas-charged sediments reaching from the sea-floor to a sub-bottom depth of about 23 m. Using the lateral distribution and thickness of the gas-charged sediments in conjunction with a mean concentration of gas of 3000 ppb, the present amount of trapped gas is estimated to be 6·45 × 10¹¹ g CH₄. The flux of methane through the sea-bed into the water column appears to be 7·2 × 10¹⁰ g CH₄ per year. To explain the small difference in size between the methane pool in near-surface sediments and the annual flux through the sea-bed, a constantly high supply of methane from leaking hydrocarbon reservoirs at greater depths has to be active.  相似文献   

The relationship between seagrass (Posidonia oceanica) decline and sulfide porewater concentration in carbonate sediments   总被引：2，自引：0，他引：2  

Maria Ll. Calleja  Núria Marb  Carlos M. Duarte 《Estuarine, Coastal and Shelf Science》2007,73(3-4):583-588

In this study we test the hypothesized negative relationship between seagrass status and porewater hydrogen sulfide (H₂S) levels, through a comparative analysis within a range of seven Posidonia oceanica meadows growing over carbonate sediments in the NW Mediterranean Sea around Mallorca Island. The studied meadows range from meadows growing on sediments with very low sulfide porewater concentrations (4.6 μM) to those growing over higher sulfide conditions (33.5 μM). Organic matter content, sulfate reduction rates and sulfide porewater concentrations in the sediments were determined concurrently with the assessment of demographic plant dynamics (specific mortality and net population growth rates). Sulfide porewater concentration increased with increasing organic matter content in the sediment, while net population growth decreased significantly with low increases of sulfide concentrations. Our results confirm the previously suspected vulnerability of seagrass meadows growing on carbonate sediments to increased sulfide levels. An excess of 10 μmols H₂S L⁻¹ porewater is identified to already conduce P. oceanica meadows to decline, which this study identifies, particularly, as strongly sensitive to sulfides. The results reported here suggest that even moderate increases in organic carbon inputs may lead to enhancement of dissolved sulfides and may be an important factor for seagrass status in these iron-depleted carbonate sediments from the Mediterranean Sea.  相似文献   

Rare earth elements-rich phase and enriching mechanism in sediments from CC area, the Pacific Ocean   总被引：1，自引：0，他引：1  

Meng Xianwei  Chen Zhihu  Wang Xiangqin  Liu Na 《海洋学报(英文版)》2001,20(2):209-214

Compared to North American shale composition (NASC),REE contents of sediments from the CC area in the Pacific Ocean are obviously high except that cerium has equal content to that of NASC.Three-valence rare earth elements were completely enriched in phosphate-phase and cerium in iron-phase.Rare earth elements in the sediments were originally derived from seawater.During lithigenic and minerogenic processes of metalliferous nodules,three-valence rare earth elements in sediments mobilized and incorporated into sediments as authigenous biogenic-apatite,while cerium had change from Ce³⁺ to Ce⁴⁺ and directly precipitated from seawater and entered metalliferous nodules and caused Ceanomalies in REE pattern in sediments.  相似文献   

A Sound Approach to Soft Sediment Resolution     

M. Snoek 《Marine Geophysical Researches》2005,26(2-4):275-286

The last few years has seen a surge in research activities directed towards investigating properties and dynamics of young marine, limnic and fluvial sediments. It is by now a well established fact that the sequence of sediments ranging from concentrated benthic suspension over fluid mud to un-consolidated material summarized as liquid sediments (LS), act as carriers for a wide range of pollutants discharged or migrated into waterways. Knowledge of the transport and fate of LS allows determining the transport and fate of adsorbed constituents (e.g., heavy metals, pesticides, PCBs, PAHs). To assess the environmental impact of LS, efforts have to be made to better understand the processes in relation to hydrodynamics and the chemical and physical properties of the layers. Since physical laws limit the resolution and detection power of conventional seismo-acoustic systems in respect of LS, alternative measurement, data analysis and processing approaches have to be found. Adapted acoustic procedures initially developed for shallow water marine environments to extreme shallow water regimes using matched field inversion techniques can reveal geoacoustic parameters including density, compressional wave speed and attenuation as a function of depth and time. The paper outlines the effects of sediment mobility upon the environment followed by a short overview of techniques commonly used to investigate sediments and other freshwater/marine events. The problems faced and limitations of existing systems are briefly outlined. Results obtained with recently developed and refined geoacoustic inversion methods are presented highlighting their potential for long-term study of physical properties and dynamics of LS.  相似文献   

东海天然气水合物的地球化学标志与找矿远景   总被引：5，自引：1，他引：5  

卢振权  龚建明  吴必豪  陈建文  邓坚 《海洋地质与第四纪地质》2003,23(3):77-81

利用大量的海底沉积物样品，开展了东海天然气水合物卫星热红外遥感和沉积物酸脱气地球化学找矿研究。根据卫星热红外增温异常和海底浅表层沉积烃类异常及其他各种异常标志，可以预测冲绳海槽中南部海域为最可能的水合物赋存区。  相似文献   

主频计算法对测井曲线沉积旋回的精细分析   总被引：5，自引：0，他引：5  

吕炳全  王红罡  赵会民  张彦军 《海洋地质前沿》2002,18(4):27-30

用主频计算法对长庆气田主力储层中下奥陶统马家沟组马五1段碳酸盐岩的自然伽玛测井曲线进行了分析，得出其主要沉积旋回周期为100、57、36和26ka，基本与米兰科维奇旋回的地球自转偏心率和地轴倾角变化周期相一致，因崦，可以认为储层的沉积旋回是地球自转偏心率和地轴倾角变化引起气候周期性变化形成的，其中又以偏心率影响最大，表明主频计算法用于测井曲线进行分辩率较高的沉积旋回分析是可行的。  相似文献   

海洋沉积粘土矿物与全球变化研究的探讨   总被引：6，自引：0，他引：6  

孔祥乐  项海光 《海洋湖沼通报》2003,(1):22-26

本文对我国粘土矿物的科研成果进行了初步综述，概述了海洋沉积粘土矿物在全球变化研究中的作用，探讨了海洋沉积粘土矿物的古环境，古气候指示意义。  相似文献