Recent and Late Holocene environments on the southeastern shelf of the Laptev Sea as inferred from microfossil data

The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (～last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (～600–1100 years B.P.) and the Little Ice Age (～100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ～5100–6200 years B.P.     

Wave runup on a concentric twin perforated circular cylinder

The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements.     

On the radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas

The radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas of finite depth is investigated. The analytical expressions for the radiated and diffracted potentials are derived as infinite series by use of the method of separation of variables. The unknown coefficients in the series are determined by the eigenfunction expansion matching method. The expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are given and verified by the boundary element method. Using the present analytical solution, the hydrodynamic influences of the angle of incidence, the submergence, the width and the thickness of the structure on the wave forces, hydrodynamic coefficients, and reflection and transmission coefficients are discussed in detail.     

Wave interaction with a perforated wall breakwater with a submerged horizontal porous plate

This study examines the hydrodynamic performance of a new perforated-wall breakwater. The breakwater consists of a perforated front wall, a solid back wall and a submerged horizontal porous plate installed between them. The horizontal porous plate enhances the stability and wave-absorbing capacity of the structure. An analytical solution based on linear potential theory is developed for the interaction of water waves with the new proposed breakwater. According to the division of the structure, the whole fluid domain is divided into three sub-domains, and the velocity potential in each domain is obtained using the matched eigenfunction method. Then the reflection coefficient and the wave forces and moments on the perforated front wall and the submerged horizontal porous plate are calculated. The numerical results obtained for limiting cases are exactly the same as previous predictions for a perforated-wall breakwater with a submerged horizontal solid plate [Yip, T.L., Chwang, A.T., 2000. Perforated wall breakwater with internal horiontal plate. Journal of Engineering Mechanics ASCE 126 (5), 533–538] and a vertical wall with a submerged horizontal porous plate [Wu, J.H., Wan, Z.P., Fang, Y., 1998. Wave reflection by a vertical wall with a horizontal submerged porous plate. Ocean Engineering 25 (9), 767–779]. Numerical results show that with suitable geometric porosity of the front wall and horizontal plate, the reflection coefficient will be always rather small if the relative wave absorbing chamber width (distance between the front and back walls versus incident wavelength) exceeds a certain small value. In addition, the wave force and moment on the horizontal plate decrease significantly with the increase of the plate porosity.     

Gradation affects basic mechanical characteristics of Chinese calcareous sand as airport subgrade of reefs

Abstract

Construction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content.     

中国近海的蔓足类 Ⅰ.藤壶属

藤壶属(Genus Balanus)是甲壳类蔓足亚纲(Subclass Cirripedia)藤壶科(Family Balanidae)中最大的一属，它在有害海洋附着生物中是主要组成成分。许多种附着于船底、水下设施或建筑物上，致使船舰燃料消耗增加，航速减低，降低浮标浮力，缩小管道通路，侵占某些水产养殖对象的有效附着面，污损养殖架筏和绳索，加快水下金属的腐蚀等，对海防、海运交通、工业和渔业常造成一定危害，同人类的关系颇为密切。随着我国科学事业的发展，特别是附着生物防除工作的进展，对于种类的确切鉴定和生物学及生态学资料需要日益增多，只有在搞清种类的基础上，根据不同种的生物学和生态特征，采取相应的措施，才能有效地进行防除工作。 中国近海的藤壶属，国内外仅有一些零星记载，缺乏全面而系统的报告。我们早在五十年代，就注意到我国沿海常见的一些主要附着生物，特别是当时作为“布纹藤壶” Balanus Amphitrite communis Darwin(=B.reticulatus Utinomi)和“克氏藤壶”Balanus Amphitrite krügeri Nilsson-Cantell(=B.uliginosus Utinomi)描记的两个类型，无论在栖息环境、繁殖习性或幼虫形态上都有显著差异，因而怀疑它们不是一个种内的亚种，而应属于不同的种。为了解决上述和类似的问题，给生态和防除研究工作提供更为准确的基本资料，我们对藤壶亚目的种类进行了系统的研究，本文是研究报告的第一部分。根据的是中国科学院海洋研究所历年采集收藏的标本，共鉴定31种和亚种，分隶于7个亚属，其中有6新种，有9种在我国是首次记录(种名录见190页)。新种的模式标本均保存于中国科学院海洋研究所。     

Estimation of the oxygen and CO2 mean exchange between the ocean and the atmosphere in key areas of the ocean

Current estimations of gas exchange between the ocean and the atmosphere are based on the concepts about diffusive gas transfer across the interface and about a stationary character of the processes; however, under a strong wind, these concepts are invalid. Transfer equations for gas constitutents of the air are incorporated into a numerical model of a nonstationary upper layer of the ocean. These equations contain the source function—gas transfer by bubbles, which becomes noticeable even at a wind speed of 8–10 m/s. The fluxes of oxygen and CO₂ are calculated at a specified wind speed, dependences of these fluxes on the wind speed are constructed, and estimates for the average annual fluxes are obtained for several areas of the Gulf Stream and Kuroshio. A substantial change in the difference of the air-water gas contents under a strong wind, caused by the turbulent exchange growth and appreciably affecting the gas exchange, is noted. The influence of the carbonate system of seawater on the CO₂ transfer during a storm is estimated. The results obtained are compared to the estimates based on the traditional approach.     

Principal features of the World Ocean climate change in the Cenozoic and their possible causes

The objective of this study was to present details of the evolution of the thermal field of the ocean during the last Cenozoic glacial megacycle. The main causes of the phenomena observed are discussed based on the generalization of original data accumulated during many years and numerous publications. It is shown that, in the Eocene and Early Oligocene, the climatic conditions in the World Ocean were uniform and featured no evident zonal differences, the meridional temperature gradients were low, and the mean global temperature was close to the present-day value. Starting from the Late Oligocene and throughout the entire Neogene, the meridional contrasts in the temperature and hydrological conditions have increased, and, in the Late Pliocene, the climatic pattern resembled the present-day situation. The general tendency in the climate changes since the Eocene until the Pliocene consisted of its latitudinal differentiation and growing contrasts rather than of general climate cooling. In the Pleistocene, with the onset of the glaciation in the Northern Hemisphere, the character of the temperature field changed and variations in the mean global temperature values began to dominate. The factors that result from the climate changes observed are discussed and the causes are shown that lead to the differences between the author’s data and the existing concepts.     

Palynological characterization of gassy sediments in the inner part of Ría de Vigo (NW Spain). New chronological and environmental data

Palynological characterization of the pollen assemblages from core ZV-01 offers a reliable age record of shallow ‘gas seal’ and ‘gas reservoir’ sediments from the Ría de Vigo (NW Spain). Gassy sediments show a direct correspondence with the palynological assemblage zones (LPAZ) 2, 3 and 4, which range in age from 950 to 1510 a.d. for the interval 81–176 cm where gas is found. The facies acting as a seal would correspond to the sedimentation in the ria starting from 1510 a.d. These assemblages also provide significant data which make it possible to reconstruct the palaeoenvironmental changes recorded in the sedimentary infill of the Ría de Vigo. The gassy horizon corresponds to the phase when riparian and mesophilous forest were better represented. This coincides with a relative high abundance of Lingulodinium machaerophorum, which indicates that the waters of the ria had been less renewed by oceanic waters and had a plentiful supply of continental nutrients. At that time, anoxic conditions resulted from restricted vertical circulation of seawater and/or high biological productivity. The dinocyst assemblages overlying and underlying the gassy horizon in core ZV-01 are clearly different from those concomitant with the accumulation of the gassy sediments. This suggests that oceanographic conditions in the Ría de Vigo may have changed several times during the time interval covered by our record. The weaker relationship between L. machaerophorum/Spiniferites spp., and simultaneous significant increases in Impagidinium spp. and Bitectatodinium tepikiense may indicate a greater intrusion of colder, more oceanic waters into the Ría de Vigo, which may have provoked intensification in upwelling during two periods, ca. 700–850 a.d. and ca. 1500–1750 a.d.