A finite volume discretization of the pressure gradient force using analytic integration

Layered ocean models can exhibit spurious thermobaric instability if the compressibility of sea water is not treated accurately enough. We find that previous solutions to this problem are inadequate for simulations of a changing climate. We propose a new discretization of the pressure gradient acceleration using the finite volume method. In this method, the pressure gradient acceleration is exhibited as the difference of the integral “contact” pressure acting on the edges of a finite volume. This integral “contact” pressure can be calculated analytically by choosing a tractable equation of state. The result is a discretization that has zero truncation error for an isothermal and isohaline layer and does not exhibit the spurious thermobaric instability.     

Nutrient contributions to the Santa Barbara Channel, California, from the ephemeral Santa Clara River

The Santa Clara River delivers nutrient rich runoff to the eastern Santa Barbara Channel during brief (1–3 day) episodic events. Using both river and oceanographic measurements, we evaluate river loading and dispersal of dissolved macronutrients (silicate, inorganic N and P) and comment on the biological implications of these nutrient contributions. Both river and ocean observations suggest that river nutrient concentrations are inversely related to river flow rates. Land use is suggested to influence these concentrations, since runoff from a subwatershed with substantial agriculture and urban areas had much higher nitrate than runoff from a wooded subwatershed. During runoff events, river nutrients were observed to conservatively mix into the buoyant, surface plume immediately seaward of the Santa Clara River mouth. Dispersal of these river nutrients extended 10s of km into the channel. Growth of phytoplankton and nutrient uptake was low during our observations (1–3 days following runoff), presumably due to the very low light levels resulting from high turbidity. However, nutrient quality of runoff (Si:N:P = 16:5:1) was found to be significantly different than upwelling inputs (13:10:1), which may influence different algal responses once sediments settle. Evaluation of total river nitrate loads suggests that most of the annual river nutrient fluxes to the ocean occur during the brief winter flooding events. Wet winters (such as El Niño) contribute nutrients at rates approximately an order-of-magnitude greater than “average” winters. Although total river nitrate delivery is considerably less than that supplied by upwelling, the timing and location of these types of events are very different, with river discharge (upwelling) occurring predominantly in the winter (summer) and in the eastern (western) channel.     

Transitional waters: A new approach, semantics or just muddying the waters?

Estuarine, Coastal and Shelf Science has throughout its history considered a diverse range of habitats including estuaries and fjords, brackish water and lagoons, as well as coastal marine systems. Its articles have reflected recent trends and developments within the estuarine and coastal fields and this includes the changing use of well-accepted terms. The term “transitional waters” first came to prominence in 2000 with the publication of the Water Framework Directive of the European Communities [European Communities, 2000. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy. Official Journal of the European Communities 43 (L327), 75 pp.], where “transitional waters” are defined as “bodies of surface water in the vicinity of river mouths which are partially saline in character as a result of their proximity to coastal waters but which are substantially influenced by freshwater flows”. The inclusion of the term transitional waters in our own aims and scope reflects the evolution of language in this subject area, encompassing tidal estuaries and non-tidal brackish water lagoons. This article reflects on some of the difficulties posed by the use of the term and its attempts to be inclusive by incorporating fjords, fjards, river mouths, deltas, rias and lagoons as well as the more classical estuaries. It also discusses the problems of including in the term river mouths discharging either into predominantly brackish areas such as the Baltic Sea, or into freshwater-poor areas bordering the Mediterranean.     

Strengths and weaknesses of the global ocean conveyor: Inter-basin freshwater disparities as the major control

According to the current paradigm of modern climatology and oceanography, the global ocean thermohaline circulation works as the so-called “global ocean salinity conveyor belt” – a system of currents connecting different ocean basins and most notably – the northern North Atlantic and northern North Pacific Oceans – the most distant regions of the world ocean. It is shown here that a slight disparity in freshwater redistribution between the Atlantic and Pacific oceans can be sufficient for building up and maintaining a global conveyor-type ocean thermohaline circulation. On the other hand, relatively small changes in this disparity leading to change in sea surface salinity contrasts between and in the north-south within the northern parts of these two oceans can easily change the conveyor.     

Study of a wave energy device for possible application in communication and spacecraft propulsion

A possible scheme for utilizing ocean wave energy to generate a high power laser is examined. Such a laser can be used (i) unguided communication under water or through the atmosphere, and (ii) in spacecraft propulsion. The natural frequencies and the frequency response of the proposed two degree-of-freedom primary energy converter are obtained by using Lagrange's equations. Further, it is shown that the basic principle used in primary energy conversion can be developed into a mechanism for roll stabilization of marine vessels.     

The “separation formula” and its application to the Pacific Ocean

The “separation formula”, a new method for computing the adiabatic inter-hemispheric meridional transport, is applied to the Pacific Ocean. The method involves an integration of the wind stress along a “horseshoe” path. It begins at the separation point of the East Australian Current, continues eastward across the ocean, progresses northward along the continental boundary, and then turns back westward across the ocean to the separation point of the Kuroshio. Since the Pacific is closed on the northern side, such an integration gives the wind-driven Indonesian throughflow.The analytical formulas show that, in order for the adiabatic wind-driven throughflow to exist, it is necessary that there be an asymmetry in the winds associated with the two zonal cross-sections connecting the (northern and southern) separation points in the west to the continents in the east. It turns out that these asymmetries in the Pacific are relatively small and, consequently, do not allow for a significant (i.e. more than one Sverdrup) Indonesian transport. Specifically, in the Pacific, this wind-driven transport is directed to the south, implying a very small net Indian-to-Pacific transport rather than a Pacific-to-Indian transport. The adiabatic model fails, therefore, to explain the observed Pacific-to-Indian throughflow of 5-6 Sv.When an upwelling is added to the model (to simulate diabatic processes), then one obtains the result that all the water upwelled in the Pacific must exit the Pacific via the Indonesian seas, i.e. the wind field is effectively blocking the oceanic region between Australia and South America, forcing the upwelled water into the Indian Ocean. This model suggests, therefore, that the observed Pacific-to-Indian throughflow is a measure of the upwelling in the Pacific.     

深水滑翔机器人耐压壳体结构优化设计

针对深水滑翔机器人耐压壳体在深水中压缩变形和海水密度随水深增大而变化等因素造成驱动浮力变化问题,利用压缩变形和密度变化对驱动浮力影响的互补特性,归纳了载体耐压壳体结构优化设计方法.保证耐压壳体抗压条件和质量最小前提下采用结构优化设计方法,降低耐压壳体压缩变形和海水密度变化对驱动浮力的影响,提高系统能源的利用率.     

Relevance of peat draining rivers in central Sumatra for the riverine input of dissolved organic carbon into the ocean

Sources and discharges of dissolved organic carbon (DOC) from the central Sumatran river Siak were studied. DOC concentrations in the Siak ranged between 560 and 2594 μmol l⁻¹ and peak out after its confluence with the river Mandau. The Mandau drains part of the central Sumatran peatlands and can be characterized as a typical blackwater river due to its high DOC concentration, its dark brown-coloured, acidic water (pH 4.4–4.7) and its low concentration of total suspended matter (12–41 mg l⁻¹). The Mandau supplies about half of the DOC that enters the Siak Estuary where it mixes conservatively with ocean water. The DOC input from the Siak into the ocean was estimated to be 0.3 Tg C yr⁻¹. Extrapolated to entire Indonesia the data suggest a total Indonesian DOC export of 21 Tg yr⁻¹ representing 10% of the global riverine DOC input into the ocean.     

Sediment—sea interaction

1. (1) The nature of sediment—sea interactions depends on the time scale considered. At a time scale commensurate with human life, one can define a water—sediment interface, and the main exchanges are solutes exchanges through this interface by concentration diffusion. This condition will be termed as “Short time-scale equilibrium interaction”.

On the other hand, at a geological time scale, there is a continuous accretion to the “sediment” of suspended particulate matter, bottom-current borne materials and sometimes precipitates of previously dissolved salts; to this sediment build-up corresponds a flux of water of reverse sense, from the sediment to the water column, due to the compaction of muds and oozes which reduce their porosity (their water content) under their own load. The concept of interface is then of limited utility, since physically it is constantly changing, and since the material balance of the exchanges does not depend on its characteristics at a first order of approximation. This condition will be termed “long time-scale geological interaction”.

These situations are extreme ones. In areas of present important detrital sedimentation, even for short time spans it is doubtful if the definition of an interface has some utility: we are in a situation close to “geological time scale”. On the contrary, in abyssal zones remote from continents, the rate of sedimentation is so low that even for eons an interface separating two environments in physico-chemical equilibrium exists.

2. (2) If there were no internal sources of dissolved species in the sediment, the only concentration changes to occur would be due to the decrease in porosity (in water content) following gravitational compaction of sediments. But this phenomenon is the same as sedimentation, thus transfer of matter would be unappreciable within short time spans. The fact that this transfer can be measured at human time scale shows therefore that dissolved species are actually produced in the sediment. Some of these can originate from possible inorganic chemical reactions, but all the organic molecules, and an important part of the inorganic (such as phosphates, nitrates, NH₄⁺, S^2-) require processing of organic matter for their production. Whether or not this reworking is of biological origin remains controversial. On the whole, the quantities of matter thus transferred are very minute compared to the quantities present in oceanic waters. They cannot be considered in general as a significant input. But they may be important locally (nearshore restricted water bodies, or manganese nodules formation).

3. (3) At geological time scale, sedimentation, which adds solid material to the preexisting sediment, results also in the compaction of this sediment. At every depth in the sediment there exists an equilibrium value of the porosity, i.e. the fluids content, of the sediment; it tends to this value by expelling the corresponding quantity of fluids, with a rate determined by its permeability. This input may be important, but it is mainly water, and water formerly oceanic: therefore it is not a true input, but simply a delayed return. The transfer of other fluids (mainly oil and gas) is unsignificant generally speaking. Once more, it may be locally important (submarine seepages).

4. (4) On the whole, the processes of water—sediment interaction appear not to add any new matter into the oceanic pool, but rather to regulate the restitution by the sediment to the water of substances which were already present in ocean, in particulate or dissolved form, either free or combined. One can trace out two main processes, which differ in their rates and yields:

4.1. (a) the short time scale diffusion—high rate low yield restitution of organics and inorganics in dissolved state:

4.2. (b) the long time scale compaction: low rate high yield restitution of entrapped fluids, essentially water (devoid of dissolved species).

Not only do these processes not bring any new matter to the ocean, but even the absolute quantities involved are modest compared either to the quantities present in the ocean or to the quantities generated by the photosynthetic primary production or brought by the rivers.In contrast to the insignificance of the water—sediment interaction in the oceanic material balance, this same interaction is one of the main sources for the material sedimented and especially the organic one, and therefore it is a fundamental key for all the subsequent sedimentary history.The significant inputs at the limit “bottom”-water come from the regions of deep tectonic activity, volcanism, creation of new oceanic crust etc… There tremendous amounts of substances can be brought into solution, changing at least locally the concentration equilibrium values of seawater. They are of course inorganic ions, but they can have important biological consequences. The buffering capacity of the world ocean is so high that only cosmic events can influence its composition.     

Sea ice–ocean coupling using a rescaled vertical coordinate z

Realistic representation of sea ice in ocean models involves the use of a non-linear free-surface, a real freshwater flux and observance of requisite conservation laws. We show here that these properties can be achieved in practice through use of a rescaled vertical coordinate “z^*” in z-coordinate models that allows one to follow undulations in the free-surface under sea ice loading. In particular, the adoption of “z^*” avoids the difficult issue of vanishing levels under thick ice.Details of the implementation within MITgcm are provided. A high resolution global ocean sea ice simulation illustrates the robustness of the z^* formulation and reveals a source of oceanic variability associated with sea ice dynamics and ice-loading effects. The use of the z^* coordinate allows one to achieve perfect conservation of fresh water, heat and salt, as shown in extended integration of coupled ocean sea ice atmospheric model.     

Transverse vibrations of circular annular plates with edges elastically restrained against rotation, used in acoustic underwater transducers

Simply supported or clamped boundary conditions are rather ideal situations difficult to satisfy from a physical viewpoint. This paper considers a more “moderate” restriction: the case of edges elastically restrained against rotation for which no exact solution appears in the open literature. Eigenvalues corresponding to a wide range of the intervening geometric and mechanical parameters are determined. Good agreement is obtained with frequency coefficients determined two decades ago by means of a variational method. Obviously the problem is of basic interest in many ocean engineering applications: from the design of certain underwater acoustic transducers to pump and compressor elements passing through the design of naval vehicles and ocean structures.     

Verification studies for a z-coordinate primitive-equation model: Tidal conversion at a mid-ocean ridge

We document the accuracy and convergence of solutions for a z-coordinate primitive-equation model of internal tide generation and propagation. The model, which is based on MOM3 numerics, is linearized around a state of rest to facilitate comparison with analytic estimates of baroclinic generation at finite-amplitude topography in a channel forced by barotropic tidal flow at its boundaries. Unlike the analytical model, the numerical model includes mixing of both buoyancy and momentum, and several definitions of “baroclinic conversion” are possible. These are clarified by writing out the energetics of the linearized equations in terms of barotropic kinetic energy, baroclinic kinetic energy, and available potential energy. The tidal conversion computed from the model, defined as the rate of conversion of barotropic kinetic energy into available potential energy, agrees well with analytical predictions. A comparison of different treatments of bottom topography (full-cells, partial-cells, and ghost-cells) indicates that the partial-cell treatment is the most accurate in this application. Convergence studies of flow over a smooth supercritical ridge show that the dissipation along tidal characteristics is, apparently, an integrable singularity. When the ocean bottom is not smooth, the accuracy and convergence of the model depend on the power spectrum of the topography. A numerical experiment suggests that the power spectrum of the resolved topography must roll off faster than k⁻² to obtain convergent results from a linear numerical model of this type.     

Estimates of Energy Dissipation Rates in the Three-Dimensional Deep Ocean Internal Wave Field

Using the “Eikonal Approach” (Henyey et al., 1986), we estimate energy dissipation rates in the three-dimensional Garrett-Munk internal wave field. The total energy dissipation rate within the undisturbed GM internal wave field is found to be 4.34 × 10⁻⁹ W kg⁻¹. This corresponds to a diapycnal diffusivity of about 0.3 × 10⁻⁴ m²s⁻¹, which is less than the value 10⁻⁴ m²s⁻¹ required to sustain the global ocean overturning circulation. Only when the high vertical wavenumber, near-inertial current shear is enhanced can diapycnal diffusivity reach ∼10⁻⁴ m²s⁻¹. It follows that the energy supplied at low vertical wavenumbers and low frequencies is efficiently transferred to high vertical wavenumbers and near-inertial frequencies in the mixing hotspots in the real ocean.     

A painting type of flexible piezoelectric device for ocean energy harvesting

Energy harvesting using piezoelectric materials can be realised by periodic external force. Piezoelectric material directly converts strain energy into electric power to capture a wasted ambient kinetic energy. This recovered energy can be used for operating wireless sensors, such as those found in environmental monitoring, mechanical sensing and structural diagnostic. In our previous work, a flexible piezoelectric device, FPED, was proposed and developed as an energy harvester for generating electric power from flow-induced vibration in ocean and wind environments. In this study a FPED with a painted piezoelectric layer, highly durable in order to withstand extreme bending and weathering caused by waves and currents, is proposed and developed by spray coating for use as an ocean energy harvester. A numerical method is developed to predict electro-fluid–structure interactions and to evaluate electrical performance and mechanical behaviours of the painted FPED. Additionally, validation of the numerical model is provided through several experimental tests. This study also investigates the relationship between the stiffness of the painted FPED and the vibrated frequency, as well as determining their influence on the electrical performance. Finally, the outcomes from a field test, conducted in real ocean space, is presented to provide information on electrical performance, mechanical behaviours and durability of painted FPEDs. The paper shows that a painted FPED is a useful and robust energy harvester for generating electric power from harsh environments.     

盐度定义狭义性与广义性

通过理论分析和实验验证,论述了“实用盐标”、“氯度盐标”定义的狭义性及应用范围,指出电导法和氯度法测定保守性质样品,数据正确;而测定非保守性质样品,测定值偏离绝对盐度S_a.笔者建议的“密度盐标”属于广义性质,可广泛应用于保守和非保守性质样品.密度盐标具有的优点是:(1)不受样品组成变化影响,只与溶液质量和浮力有关,测定值有高度可靠性与重现性;(2)测定大洋水盐度与现有实用盐度值相同,测定工业水盐度较实用盐度、氯度盐度值更接近绝对盐度S_a;(3)在已知溶质情况下,应用溶液膨胀系数和物质偏摩尔体积校正系数可统一溶质浓度与盐度的换算关系.     

长江口北支潮汐能源的综合利用

长江口北支有着丰富的潮汐能源及淡水，航运、水产等资源，因长期未加规划、治理，以致远未开发利用，反使河道淤浅，迳流减少，通航能力降低，且有大量泥沙，盐倒灌南支，恶化航道、水质，亟待整治、开发。研究提出，北支潮汐能可有效地用以发电和疏浚河道。可利用北支有利的河势，建造大、小双库开发方式的潮汐电站，并利用该河上、下游端间具有潮时差的有利因素，使电站可以连续不断发电、供电。同时可利用建造的上、中、下游三座水闸，逐级集水攻沙，冲刷航道淤沙，提高通航能力，实现江、海直接联运。另可兼收淡水供应，水产养殖、旅游，以及沟通崇明岛与苏北的陆上交通等效益，潮汐电站工程可采用现实可行的新技术、新材料、新的结构形式，以降低造价，使我国潮汐能得到充分开发利用。     

Bifurcation analysis of wind-driven flows with MOM4

In this paper, the methodology of bifurcation analysis is applied to the explicit time-stepping ocean model MOM4 using a Jacobian–Free Newton–Krylov (JFNK) approach. We in detail present the implementation of the JFNK method in MOM4 but restrict the preconditioning technique to the case for which the density distribution is prescribed. For a prescribed density field case, we present bifurcation diagrams, for the first time in MOM4, for the wind-driven ocean circulation. In addition, we show that the JFNK method can reduce the spin-up time to a steady equilibrium in MOM4 considerably if an accurate solution is required.     

一种计算有限水深波能功率的新方法

海洋波浪能平均功率的准确计算是波浪能开发和利用的基础。实践中，波浪能转换装置一般安装在有限水深区域。对于随机波，只有当详尽的波浪谱已知的时候，有限水深区的波能功率才能被准确计算出来。由于种种原因，实践中波浪的实测数据大多以散点图或有义波高和统计波周期的形式给出，而波浪谱信息有时则很难获得。基于这种情况，传统上人们利用无限水深条件下的相关公式来估算有限水深区域的波能功率，但这种做法会造成较大的误差。本研究显示，对于50 m水深的理论波谱JONSWAP谱来说该误差高达14.6%。为了提高波能功率计算的准确性，本文提出了一种基于能量频率的一阶和二阶近似算法，可以在未知波浪谱的情况下较为准确地计算不同水深时的波能功率。针对两种理论波浪谱的计算结果表明，本方法在计算有限带宽内的波能功率时计算误差低于2.8%。     

High-resolution sea ice in long-term global ocean GCM integrations

The resolution of the sea-ice component of a coarse-resolution global ocean general circulation model (GCM) has been enhanced to about 22 km in the Southern Ocean. The ocean GCM is designed for long-term integrations suitable for investigations of the deep-ocean equilibrium response to changes in southern hemisphere high-latitude processes. The space and time scales of the high-resolution sea-ice component are commensurate with those of the resolution of satellite passive-microwave sea-ice data. This provides the opportunity for a rigorous evaluation of simulated sea-ice characteristics. It is found that the satellite-derived continuous high ice concentration of the interior winter ice pack can only be captured when vertical oceanic mixing is modified in a way that less local, intermittent convection occurs. Furthermore, the width and the variability of the coastal polynyas around the Antarctic continent and its ice shelves are best captured when some form of ice-shelf melting is accounted for. The width of the wintertime ice edge is reasonably reproduced, while its variability remains underestimated, closely following the coarse-grid pattern of the ocean model due to its high dependence on ocean temperature. Additional variability besides daily winds, e.g. in form of idealized tidal currents, improves the temporal and spatial ice-edge variability, while leads in the interior ice pack become more abundant, more in line with the fine-scale satellite-derived texture. The coast- or ice-shelf line is described on the fine grid based on satellite passive-microwave data. This method requires parts of a coarse coastal ocean grid cell to be covered by an inert layer of “fast ice” or “ice shelf”. Reasonable long-term global deep-ocean properties can only be achieved when these areas are not inert, i.e. are exposed to heat flux and ice growth, or when the vertical mixing parameterization allows for excessive open-ocean convection. The model area exposed to cold high-latitude atmospheric conditions thus being most decisive for a realistic representation of the long-term deep-ocean properties, suggests that high-latitude coastlines are definitely in need of being represented at high resolution, including ice sheets and their effects on the heat and freshwater flux for the ocean.     

An energy conversion system based on deep-sea pressure

A novel seawater pressure energy conversion system that utilizes seawater pressure to generate electricity has been studied in this paper. The energy conversion system utilizes the pressure difference between the pressurized seawater and the empty pressure container to drive hydraulic motor and the coaxially coupled generator to generate electric power. The output electric energy is recorded by the data logger throughout the process. In the current study, technical analysis is performed with the emphasis on conversion efficiency between seawater pressure energy and output electric energy. The analysis is conducted at various pressure differences through the throttle valve so as to obtain maximum conversion efficiency. Research shows that the optimum pressure difference through the throttle valve and the maximum conversion efficiency can be theoretically calculated when the properties of the conversion system are given. Simulation results have demonstrated the influence of pressure difference on conversion efficiency. The test apparatus has been designed, built and tested in 2004. It successfully generated electric energy of approximately 0.85 kW h at the depth of 2400 m with empty pressure container's holding capacity of 200 L in the voyage “DY105-16” in South China Sea on June 12, 2004. The actual conversion efficiency from seawater pressure energy to electric energy reaches as high as 63.8% which is attractive for underwater equipments. The success of the experiment has tested the feasibility of utilizing seawater pressure energy and brings a new power supply way for long-term in-situ underwater equipments.