Experimental study on the nonlinear pressure acting on a high-speed vessel in irregular waves

The present study focuses on the nonlinear behavior of pressure on the hull surface of a high-speed vessel in irregular waves, particularly the pressure responses of alternately wet and dry areas near the waterline and on the bow zone. The vessel has high deadrise angles that may be subject to slight impact and water pile-up effects. A series of experiments in regular and irregular head waves were conducted, and the validity of applying Volterra modeling was investigated. In a previous article using experimental data in regular waves, it was confirmed that the approximate third-order Volterra model adequately simulated the variation of pressure responses in regular waves of different steepness up to a wave amplitude with a wavelength ratio of 0.01, even for the highly nonlinear pressures acting on the abovementioned areas of the hull surface. In this article, further validation for the second part of the study was obtained using experimental data in irregular waves. The frequency response functions obtained from the previous study’s experimental data in regular waves were applied to the third-order Volterra model by combining the input of irregular waves to simulate the responses in irregular waves of sea state five. Then, the spectra and statistics were analyzed. For the motions, accelerations, and pressure responses in irregular waves (as well as for the simulated time histories) variance spectra and statistics such as cumulative distributions of peak values and probability density functions were compared with the experimental results. It was confirmed that even for highly nonlinear and non-Gaussian pressures on the abovementioned areas of the hull surface, the approximate third-order Volterra model simulates the pressure responses in irregular head waves up to a sea state of five with adequate accuracy on deterministic and statistical bases.     

渤海海域建立特别敏感海域PSSA的思考

渤海拥有丰富的海洋资源,但随着经济建设的快速发展,渤海正承受前所未有的环境压力,严峻的环境污染不仅制约着环渤海经济的快速发展,也严重威胁人们的身体健康。如在渤海海域建立PSSA,对渤海海域环境综合整治以及生态恢复与保护具有极其重要的现实意义。     

An Overview of Spatial Management and Marine Protected Areas in the East China Sea

Marine ecosystems of the East China Sea are rich in biodiversity, with 12,933 species of which approximately 47.7% are endemic. As anthropogenic impacts are intensifying, fishery resources and biodiversity in the East China Sea are under threat from overfishing, habitat loss, pollution, and biological invasions. Marine protected areas (MPAs) and other spatial management measures are believed useful tools to protect and restore biological resources. Seventeen nature reserves, seven special marine reserves, and three fishery resource conservation zones covering a combined area of 102,156 km² have so far been established in the Chinese East China Sea in order to protect fishery resources, biodiversity, and marine landscapes. This article provides a review and inventory of MPAs in the Chinese East China Sea as implemented by the People's Republic of China.     

Spatial and temporal variability in the pelagic ecosystem of the East Sea (Sea of Japan): A review

The East Sea (Sea of Japan) is a unique marginal sea because it exhibits features of oceanic dynamics of much larger ocean basins. This semi-enclosed basin may be considered as a model or microcosm for understanding of how biological processes and distributions in pelagic ecosystem are interacting with physical processes in highly dynamic ocean regions. This overview summarizes the recent progresses concerning spatial and temporal variability of pelagic ecosystem components form an interdisciplinary point of view. Spatial characteristics of physical environments and biogeography in the region are distinguished mainly by the subpolar front. It was also found that long-term changes in biomass and community structure as well as those in the physical and biological environments are associated with climate variability in the region. We conclude by identifying main needs for the information and researches, particularly regular and long-term sampling, and permanent monitoring if possible.     

Response of the Black Sea mean level to atmospheric pressure and wind forcing

The response of the Black Sea mean level to atmospheric pressure (AP) and wind forcing is investigated using 5 years of TOPEX/POSEIDON (T/P hereafter) data. A coherence analysis is first applied to mean sea level and pressure to examine the validity of the inverse barometer (IB) approximation over this area. As expected, it reveals very significant deviations from an IB response attributed to the narrowness of the Bosphorus Strait and its limiting role in water exchanges. A comparison is drawn with the Mediterranean Sea case. A single basin version of the Candela analytical model [Candela, J., 1991. The Gibraltar Strait and its role in the dynamics of the Mediterranean Sea. Dyn. Atmos. Oceans 15, 267–300], which takes linear friction at the strait into account, is then used. The model explains a significant part of the T/P mean sea level variance (about 30%, while the IB correction only explains 5% of its variance) and provides a means to correct the altimeter data for the pressure effect much better than the standard IB effect. The response of the mean sea level to wind forcing is then analysed. Coherence analysis between sea level and along-strait wind stress (WS) reveals a significant coherence at periods ranging from 40 to 100 days, with an almost steady phase of 270°. This result is confirmed with a multiple coherence analysis (mean sea level vs. WS and AP). A plausible mechanism is a piling-up of water at the northern or southern end of the strait due to along-strait wind forcing. The associated along-strait pressure gradient would modify the barotropic flow in the strait and then the mean sea level. Using an extension of the Candela model, we show that this mechanism is consistent with T/P mean sea level observations.     

The effect of precession-induced changes in the Mediterranean freshwater budget on circulation at shallow and intermediate depth

The Neogene marine sedimentary record of the Mediterranean basin is characterised by the regular occurrence of organic-rich layers or sapropels. These sapropels are known to correlate with the precession cycle: their deposition coincides with precession minima. This correlation is thought to be caused to a large extent by a precession-induced increase in the amount of freshwater reaching the Mediterranean Sea. In the literature, various sources of this extra freshwater have been identified and different mechanisms as to how this freshwater flux leads to sapropels have been proposed. In this study we investigate the effects of precession-induced changes in the freshwater budget using a regional ocean general circulation model of the Mediterranean Sea. Emphasis is on the effects at the surface and at intermediate depth. The forcing of the ocean model is adjusted to precession minimum conditions on a parameter by parameter basis. Novel to our approach is that the value of the required adjustments is taken from a global coupled climate model with which experiments have been performed for the present day (close to precession maximum) and precession minimum. With the ocean model we focus on the extent to which extra runoff from either south (specifically: the river Nile) or north and changes in net precipitation over the sea itself lead to a more stable stratification; this we judge by the associated reduction of the sea surface salinity and mixed layer depth in the regions of intermediate and deep water formation. Our main finding is that the effects of (1) increased discharge of the rivers coming from the north, and (2) the increase in net precipitation over the sea itself, are of equal or greater importance than that of increase in Nile discharge.     

Forecast verification of a 3D model of the Mediterranean Sea. The use of discrete wavelet transforms and EOFs in the skill assessment of spatial forecasts

The quality assessment of a nested model system of the Mediterranean Sea is realised. The model has two zooms in the Provençal Basin and in the Ligurian Sea, realised with a two-way nesting approach. The experiment lasts for nine weeks, and at each week sea surface temperature (SST) and sea level anomaly are assimilated. The quality assessment of the surface temperature is done in a spatio-temporal approach, to take into account the high complexity of the SST distribution. We focus on the multi-scale nature of oceanic processes using two powerful tools for spatio-temporal analysis, wavelets and Empirical Orthogonal Functions (EOFs). We apply two-dimensional wavelets to decompose the high-resolution model and observed SST into different spatial scales. The Ligurian Sea model results are compared to observations at each of those spatial scales, with special attention on how the assimilation affects the model behaviour. We also use EOFs to assess the similarities between the Mediterranean Sea model and the observed SST. The results show that the assimilation mainly affects the model large-scale features, whereas the small scales show little or no improvement and sometimes, even a decrease in their skill. The multiresolution analysis reveals the connection between large- and small-scale errors, and how the choice of the maximum correlation length of the assimilation scheme affects the distribution of the model error among the different spatial scales.     

Spatially Prioritizing Seafloor Mapping for Coastal and Marine Planning

Coastal and marine areas provide vital services to support the economic, cultural, recreational, and ecological needs of human communities, but sustaining these benefits necessitates a balance between growing and often competing uses and activities. Minimizing coastal zone conflict and reducing human-induced impacts to ecological resources requires access to consistent spatial information on the distribution and condition of marine resources. Seafloor mapping provides a detailed and reliable spatial template on the structure of the seafloor that has become a core data need for many resource management strategies. The absence of detailed maps of the seafloor hinders the effectiveness of priority setting in marine policy, regulatory processes, and marine stewardship. For large management areas, the relatively high cost of seafloor mapping and limited management budgets requires careful spatial prioritization. In order to address this problem, a consensus based approach, aided by decision-support tools, and participatory geographic information systems (GIS), was implemented in Long Island Sound to spatially prioritize locations, define additional data collection efforts needed, and identify products needed to inform decision-making. The methodology developed has utility for other states and regions in need of spatially prioritizing activities for coastal planning, and organizations charged with providing geospatial services to communities with broad informational needs.     

深海矢量噪声场声传播特性研究

矢量声压振速联合处理是建立在信号的声压和质点振速相位基础上,海洋环境边界对声传播的影响将改变矢量声场声压和质点振速的幅度和相位特性。文章根据南海环境条件和水下目标辐射噪声测量采用矢量简正波理论估算海面非相干偶极子噪声源和水下点声源矢量场的幅度和相位随深度的变化,并对矢量水听器测量系统获取的南海典型深度上的背景噪声数据进行了分析。结果表明:深海背景噪声声压谱级在500 Hz以下基本上不随深度变化,在500 Hz-3 kHz频段浅深度背景噪声声压谱级略高于较深深度的背景噪声声压谱级;背景噪声的垂直质点振速谱级要小于声压和水平质点振速谱级。     

关于在南海诸岛水域建立特别敏感海区的思考

文中通过分析我国在南海诸岛水域建立特别敏感海区的必要性和可行性,提出相关的申请程序和工作建议,以期达到保护海洋环境和维护国家利益的目的j     

Effects of Human Activities on the World's Most Vulnerable Coral Reefs: Comoros Case Study

Effective management of highly biodiverse and threatened reefs requires the identification of human activities driving declines on the particular reef to be managed. The island nation of the Comoros is a model setting to investigate effects of human activities on diverse and threatened coral reefs, with abundant and diverse marine life, local dependence on reef resources, and a variety of anthropogenic pressures on reefs rendering the nation vulnerable to coral reef degradation. Using data from 21 sites throughout the Comoros, we evaluated the relative influence of human activities and other natural and anthropogenic factors on benthic cover and fish richness, abundance, and biomass with the goal of providing prioritized management targets. Human activities including fishing, beach sand extraction, and beachfront housing and development had the strongest relationship with degraded reefs but with some seasonal fluctuation, while geographic patterns most consistently predicted reef degradation across seasons. Comparing analyses conducted with and without human activities as predictors, the inclusion of human activities greatly improved explanatory power. Baseline data on reef biotic composition and localized anthropogenic impacts, monitoring over time, and controlled experiments can facilitate an adaptive management approach for protecting fragile reef ecosystems in the Comoros and elsewhere.     

Study of the seasonal cycle of the biogeochemical processes in the Ligurian Sea using a 1D interdisciplinary model

A one-dimensional coupled physical–biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed at the GeoHydrodynamics and Environmental Laboratory (GHER) of the University of Liège. The ecosystem model contains 19 state variables describing the carbon and nitrogen cycles of the pelagic food web. Phytoplankton and zooplankton are both divided in three size-based compartments and the model includes an explicit representation of the microbial loop including bacteria, dissolved organic matter, nano-, and microzooplankton. The internal carbon/nitrogen ratio is assumed variable for phytoplankton and detritus, and constant for zooplankton and bacteria. Silicate is considered as a potential limiting nutrient of phytoplankton's growth. The aggregation model described by Kriest and Evans in (Proc. Ind. Acad. Sci., Earth Planet. Sci. 109 (4) (2000) 453) is used to evaluate the sinking rate of particulate detritus. The model is forced at the air–sea interface by meteorological data coming from the “Côte d'Azur” Meteorological Buoy. The dynamics of atmospheric fluxes in the Mediterranean Sea (DYFAMED) time-series data obtained during the year 2000 are used to calibrate and validate the biological model. The comparison of model results within in situ DYFAMED data shows that although some processes are not represented by the model, such as horizontal and vertical advections, model results are overall in agreement with observations and differences observed can be explained with environmental conditions.     

Sound scattering from rough bubbly ocean surface based on modified sea surface acoustic simulator and consideration of various incident angles and sub-surface bubbles’ radii

The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz–Kirchhoff–Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall–Novarini model and optimized HKF method. The extended Hall–Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.     

Optimal interpolation of sea surface temperature for the North Sea and Baltic Sea

Sea surface temperature fields of the North Sea and Baltic Sea have been constructed for the year 2001 using a multiplatform Optimal Interpolation scheme. The analyzed fields are constructed every 12 h on a 10 km spatial grid. The product is based upon observations from the three NOAA satellites 12, 14 and 16 together with a large amount of in situ observations. Space dependent covariance functions are estimated from the satellite observations and account for spatial and temporal lags. Several independent methods have been used to assess the error on the sea surface temperature product. Compared against independent in situ observations, the mean RMS difference for the year 2001 is 0.78 °C. The spatial distribution of the errors reveals that the Baltic Sea in general show higher errors than the North Sea. The error statistics throughout the year show a temporal variation of the errors with maximum during summer and winter. Tests with a varying number of satellite observations show that the accuracy of the satellite observations is the most important parameter in terms of reducing the errors on the interpolated sea surface temperature product.     

Experimental study on the nonlinear pressure acting on a high-speed vessel in regular waves

It is well known that the hydrodynamic responses of a high-speed vessel traveling in regular head waves of even moderate wave height can show significant nonlinear behavior, and so linear statistical techniques become insufficient for predicting the statistics of responses in irregular waves. On the other hand, it has been shown that an approximate third-order Volterra model is applicable to handling the statistics of some nonlinear seakeeping problems, such as motions and vertical hull girder loads. In the present study, the focus is on the nonlinear behavior of the pressure responses of the hull surface, especially on the pressures acting on alternately wet and dry areas near the waterline and on the bow zone with high deadrise angles that may be subject to slight impact and water pile-up effects. To clarify the validity of applying Volterra modeling to this problem, a series of experiments in regular and irregular head waves were carried out, and approximate third-order and fifth-order Volterra models with the proposed algorithm for finding frequency response functions (FRFs) were applied as a means of validation. In the present article, the first part of the validation was performed using experimental data in regular waves. It was confirmed that the third-order Volterra model has adequate accuracy to simulate deterministically the variation of pressure responses in regular waves of different wave steepness up to a wave amplitude to wavelength ratio of 0.01 even for the highly nonlinear pressures acting on the above-mentioned areas of the hull surface.     

Numerical simulations of seasonal and interannual variability of the Black Sea thermohaline circulation

The Black Sea general circulation is simulated by a primitive equation model with active free surface. The forcing is seasonally variable and is based on available climatic data. The model reproduces the main features of the Black Sea circulation, including the river discharge effects on the mean sea level and the Bosphorus outflow. Model results show that the simulated sea surface elevation increases in spring over the whole sea, reaching a maximum in the Danube delta area. In the same region, a minimum is observed in winter. The amplitude of the seasonal oscillations (about 8–12 cm over the whole basin) is of the same order of magnitude as the maximum horizontal variations (about 15–18 cm between the coastal areas and the basin interior). This strong signal formed mostly by river discharges, along with the seasonal variability in the other forcing functions and the local dynamics creates a well-pronounced interannual variability. The performance of the model in simulating the seasonal and interannual variability is critically analyzed, with a special attention on the cold intermediate water formation and the circulation in the upper 150 m. The simulations demonstrate that the source of intermediate waters is on the shelf, and that the water mass in the core of cold intermediate layer changes with time as a response to the periodic forcing at sea surface. This type of variability is characterized by pronounced interannual changes, proving that important differences could exist between water mass structure in different years, even when using identical atmospheric forcings each year.     

An algorithm to discover spatial–temporal distributions of physical seawater characteristics and a case study in Turkish seas

Clustering is one of the major data mining methods to obtain a number of clues about how the physical properties of the water are distributed in a marine environment. It is a difficult problem, especially when we consider the task for spatial–temporal marine data. This study introduces a new clustering algorithm to discover regions that have similar physical seawater characteristics. In contrast to the existing density-based clustering algorithms, our algorithm has the ability of discovering clusters according to the nonspatial, spatial, and temporal values of the objects. Our algorithm also overcomes three drawbacks of existing clustering algorithms: problems in the identification of core objects, noise objects, and adjacent clusters. This paper also presents a spatial–temporal marine data warehouse system designed for storing and clustering physical data from Turkish seas. Special functions were developed for data integration, data conversion, querying, visualization, analysis, and management. User-friendly interfaces were also developed, allowing relatively inexperienced users to operate the system. As a case study, we show the spatial–temporal distributions of sea surface temperature, sea surface height residual, and significant wave height values in Turkish seas to demonstrate our algorithm.     

Regional Ocean Governance in China: An Appraisal of the Clean Bohai Sea Program

In 2001 China embarked on an ambitious program to improve water quality through creation of the Clean Bohai Sea Program (CBSP). It is the first regional ocean governance program in China. The joint conference of central and local government units directed CBSP under the leadership of the State Environment Protection Administration. To meet the environmental objectives established by the joint conference local governments must pay for the program and operate it, but to date they have not been able to fully fund the effort. Although data indicate a decline of polluted discharges to the Bohai, one tabulation shows that the area of the sea that is polluted has increased each year from 2001 to 2005. Future enhancement of CBSP depends on revising incentives to better link local environmental programs and development, establishing funding mechanisms to equitably spread costs throughout watersheds, and creating comprehensive monitoring programs to better appraise program results.     

Multigrid state vector for data assimilation in a two-way nested model of the Ligurian Sea

A system of two nested models composed by a coarse resolution model of the Mediterranean Sea, an intermediate resolution model of the Provençal Basin and a high resolution model of the Ligurian Sea is coupled with a Kalman-filter based assimilation method. The state vector for the data assimilation is composed by the temperature, salinity and elevation of the three models. The forecast error is estimated by an ensemble run of 200 members by perturbing initial condition and atmospheric forcings. The 50 dominant empirical orthogonal functions (EOF) are taken as the error covariance of the model forecast. This error covariance is assumed to be constant in time. Sea surface temperature (SST) and sea surface height (SSH) are assimilated in this system.     

Biogenic silica cycle in surface sediments of the Greenland Sea

In contrast to several investigations of biogenic silica (BSi) content and recycling in surface sediments of the Southern Ocean, little is known about the benthic cycle of BSi in high northern latitudes. Therefore, we investigated the silicic acid concentration of pore water and BSi content of surface sediments from the Greenland Sea. Low BSi contents of less than 2% were observed. High-resolution (2–5 mm) BSi profiles and comparisons to trap studies suggest that only relatively dissolution-resistant siliceous components reach the seafloor. Pore water investigations reveal BSi fluxes of more than 300 mmol m⁻² a⁻¹ only for a few sites on the shelf. A statistically significant relationship between water depth and BSi rain rate reaching the seafloor was not observed. Sampling along a transect perpendicular to the marginal ice zone (MIZ) revealed no enhanced rain rate of BSi reaching the seafloor in the vicinity of the ice edge. Although the MIZ of the Greenland Sea is characterized by the enhanced export of biogenic particles from surface waters, this feature is not reflected in the benthic cycle of biogenic silica. The lack of such a relationship, which is in contrast to observations of shelf and continental margin sediments in the southern South Atlantic, is probably caused by the enhanced dissolution of BSi in the water column and highly dynamic ice conditions in the Greenland Sea.