Recent developments in “added-mass” planing theory

The results of several recent isolated investigations in planing theory are consolidated in this paper, together with new insights generated by a recent numerical solution of the vertically impacting wedge problem by Zhao and Faltinsen [(1992), Water entry of two-dimensional bodies. J. Fluid Mech. 246, 593–612]. As a result, in contrast to some earlier studies, it is found that the “wetted width” associated with the added mass is not that of the intersection of the wedge with the undisturbed water surface, but the wetted width of the splashed-up water, as originally proposed by Wagner [(1932), Uber Stoss-und Gleitvorgange an der Oberflache von Flussig-Keiten, Zeitschrift für Angewandte Mathematik und Mechanik, Band 12, Heft 4 (August)]. However, the splash-up ratio is not the value of (π/2–1) which he proposed, but a value which decreases with increasing deadrise, originally proposed in the late-1940s by Pierson (“Pierson's hypothesis” in the paper). For 30° deadrise, for example, Pierson's splash-up ratio is two-thirds that of Wagner's.The new equations are employed to determine the increase in the “added mass” of prismatic hull sections due to chine immersion, using experimental data. If m_o^′ is the added amss of the hull section whose chines are just wetted, Payne [(1988), Design of High-speed Boats. Volume 1: Planing. Fishergate, Inc., Annapolis, Maryland, U.S.A.] postulated that the increase in added mass due to a chine submergence (z_c) would be

where b is the chine beam and k is a constant which Payne [(1988), Design of High-speed Boats. Volume 1: Planing. Fishergate, Inc., Annapolis, Maryland, U.S.A.] gave as .The present analysis includes the “one-sided flow” correction introduced in Payne [(1990), Planing and impacting forces at large trim angels. Ocean Engng 17, 201–234]. Partly for that reason and partly because of the more precise analysis of the experimental data, the present paper revises the value to k = 2 for wetted length to beam ratios normally employed. For deadrise angles in excess of 40° and wetted keel to beam ratios in excess of 2.0, there is some evidence that k < 2.0.The revised theoretical formulation is compared with eight different sets of experimental data for flat plate and prismatic hull forms and is found to be in excellent agreement when the speed is high enough for “dynamic suction” (a loss of buoyancy at low speeds and low wetted lenghts) to be unimportant. This is true for “chines-dry” operation with deadrise angles up to 50° and chines-wet operation at length to beam ratios far in excess of the most extreme conventional practice.The research involved in performing this analysis led to the realization that different towing tanks measure different wetted chine lengths for the same hulls and test conditions. Some consistently measure more splash-up than “theory” (based on Pierson's splash-up hypothesis) predicts and others measure somewhat less than the theory. Some examples are given in Appendix B. The reason for this is not understood.     

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.     

Wasp-waist populations and marine ecosystem dynamics: Navigating the “predator pit” topographies

Many marine ecosystems exhibit a characteristic “wasp-waist” structure, where a single species, or at most several species, of small planktivorous fishes entirely dominate their trophic level. These species have complex life histories that result in radical variability that may propagate to both higher and lower trophic levels of the ecosystem. In addition, these populations have two key attributes: (1) they represent the lowest trophic level that is mobile, so they are capable of relocating their area of operation according to their own internal dynamics; (2) they may prey upon the early life stages of their predators, forming an unstable feedback loop in the trophic system that may, for example, precipitate abrupt regime shifts. Experience with the typical “boom-bust” dynamics of this type of population, and with populations that interact trophically with them, suggests a “predator pit” type of dynamics. This features a refuge from predation when abundance is very low, very destructive predation between an abundance level sufficient to attract interest from predators and an abundance level sufficient to satiate available predators, and, as abundance increases beyond this satiation point, decreasing specific predation mortality and population breakout. A simple formalism is developed to describe these dynamics. Examples of its application include (a) a hypothetical mechanism for progressive geographical habitat expansion at high biomass, (b) an explanation for the out-of-phase alternations of abundances of anchovies and sardines in many regional systems that appear to occur without substantial adverse interactions between the two species groups, and (c) an account of an interaction of environmental processes and fishery exploitation that caused a regime shift. The last is the example of the Baltic Sea, where the cod resource collapsed in concert with establishment of dominance of that ecosystem by the cod’s ‘wasp-waist” prey, herring and sprat.     

Forced vibration analysis of an offshore tower carrying an eccentric tip mass with rotary inertia due to support excitation

Dynamic responses of structures due to earthquake excitation are the important problems in engineering, thus, the information concerned is plenty. However, most of the literature is relating to the discrete methods, particularly to the finite element method (FEM), and the one relating to the method combining both the “continuous” and “discrete” models is rare. The objective of this paper is to provide some information in this respect. First, the analytical solution for the natural frequencies and normal mode shapes of a “continuous” tower, without contacting water (or “dry” tower), carrying an eccentric tip mass possessing rotary inertia is determined. Next, the partial differential equation of motion for the forced vibration of the tower, contacting water (or “wet” tower), subjected to support excitation is transformed into a matrix equation by using the last natural frequencies and normal modes shape of the freely vibrating dry tower. Finally, the numerical integration method is used to solve the matrix equation to yield the seismic response of the wet tower. In theory, the mode superposition method is correct only if the total number of modes considered approaches infinity, however, numerical results of this paper reveal that superposition of only the lowest six modes will yield excellent results to be very close to the corresponding ones obtained from the conventional FEM. For this reason, the CPU time required by the presented approach is less than 5% of that required by the conventional FEM.     

An improved “benchmark” method for estimating particle settling velocities from time-series sediment trap fluxes

A new method, based on fitting Fourier series to time-series (TS) data from sediment traps, was developed to estimate the settling velocities (SVs) of sinking particles in the open ocean. This new method was applied to data from MedFlux, as well as from the US JGOFS NABE, EqPac, and ASPS studies. Fluxes of mass and of four chemical tracers, as well as the molar ratios of the latter, were plotted on logarithmic scales; Fourier series were then fit to these data. In each case we determined the most likely settling velocity using a likelihood-based nonlinear fitting algorithm. Variation among estimates using single tracers was significantly less than variation using tracer ratios; we therefore concluded that estimates based on single tracers are to be preferred to estimates based on tracer ratios. Our results also showed no obvious differences among SVs estimated using different single tracers. The best estimate of settling velocity using single-tracer fluxes with good temporal resolution (i.e. for sites with cup rotation times 8.5 days) is 205 m/d, with standard deviation 74 m/d. For MedFlux data alone (which have a resolution of 4–6 days), the estimate is 220±65 m/d. This latter value is within 10% of the estimate of average settling velocity (242±31 m/d) made using MedFlux IRS traps in “settling velocity” mode.     

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.     

“Batfish” a depth controllable towed body for collecting oceanographic data

“Batfish” is a streamlined vehicle developed to house fast-responding oceanographic sensors. It is towed behind a ship or small vessel and its depth is controlled from the vessel by a manually or automatically produced command signal. Variable-angle wings permit the vehicle to be lowered and a novel control surface, which eliminates the need for heavy ballast, assures lateral stability. There are two models: the standard and the wide-wing Batfish. The standard Batfish has collected temperature and conductivity data at depths of up to 200 m when towed at 10–25 km/hr, and the wide-wing Batfish at depths to 400 m when towed at 10–16km/hr.     

A low level supplementary heating system for free divers

A simple and effective method of heating divers in extreme cold water has been developed. The local heating concept utilizes a uniformly distributed granular mixture of magnesium and iron particles packed in small sachets. Upon activation by sea water, the two metal mixture behaves as a multitude of short-circuited electrolytic cells, producing thermal energy rather than electrical energy. The 45 mm-square sachets may be placed where heating is required on the diver's body, thus giving rise to the term “local heating”, obviously, the heating system requires no pumping device, or distribution network. Heating rate and duration of output of the sachets are controlled by particle size, and mixture ratio of the constituent Mg and Fe particles.This paper described the development, testing and performance of the heating sachets. Results of live tests in different dive situations are also presented and discussed.     

The discrete methods for free vibration analyses of an immersed beam carrying an eccentric tip mass with rotary inertia

In this paper, a beam without contact with water is called the “dry” beam and the one in contact with water is called the “wet” beam. For a partially (or completely) immersed uniform beam carrying an eccentric tip mass possessing rotary inertia, the conventional analytical (closed-form) solution is achieved by considering the inertial forces and moments of the tip mass and rotary inertia as the boundary conditions at the tip end of the beam. However, it has been found that the approximate solution for the last problem may be achieved by two techniques: Method 1 and Method 2. In Method 1, the basic concept is the same as the conventional analytical method; but in Method 2, the tip end of the beam is considered as a free end, while the inertial forces and moments induced by the tip mass and rotary inertia are considered as the external loads applied at the tip end of the beam. The main differences between the formulation of Method 1 and that of Method 2 are: In Method 1, the “normal” shapes of the “dry” beam are functions of the frequency-dependent boundary conditions but the external loads at the tip end are equal to zero; On the contrary, in Method 2, the “normal” mode shapes of the “dry” beam are determined based on the zero boundary conditions at the tip end of the beam but the external loads at the tip end due to the inertial effects of the tip mass and rotary inertia must be taken into consideration for the free vibration analysis of the “wet” beam. Numerical results reveal that the approximate solution obtained from Method 2 are very close to that from Method 1 if the tip mass moment of inertia is negligible. Besides, the two approximate solutions are also very close to the associated analytical (closed-form) solution or the finite element solution. In general, it is hoped that there exist several methods for tackling the same problem so that one may have more choices to incorporate with the specified cases. It is believed that the two approximate methods presented in this paper will be significant from this point of view.     

Study on the dynamic characteristic of a U-type tuned liquid damper

By means of Lagrange's equation, the “coupled” equations of motion for a horizontal plate carrying a U-type tuned liquid damper (TLD) are derived. The “uncoupled” equations of motion for the liquid (in the TLD) and the structural system are then obtained by decoupling the “coupled” ones. Unlike the existing literature to indirectly determine the natural frequencies of a damped vibrating system by using the resonant method, the “complex” eigenvalues of the coupled damped system are obtained directly from the associated eigenvalue equations. Besides, the pressure intensities in the two air chambers and the sizes of the two vertical tanks together with the horizontal conduit are arbitrary in the formulation of this paper. The influence of some key parameters of the TLD on the dynamic responses of the structural system is studied.     

Depositional environments of the Mediterranean “Lower Evaporites” of the Messinian salinity crisis: Constraints from quantitative analyses

We use simple quantitative analyses to evaluate controversial water level scenarios for the Mediterranean “Lower Evaporites” of the Messinian salinity crisis. Our results indicate that a shallow-water scenario for the Lower Gypsum units – with Mediterranean water level lower than the sill at Gibraltar – would imply unrealistic salt thicknesses on the order of 3 km. Some outflow to the open ocean must have persisted, implying that the Mediterranean was a deep-water basin during Lower Gypsum formation. Since glacio-eustatic fluctuations do not seem to have had a major influence on Lower Gypsum deposits, Mediterranean water level was even substantially higher than the Gibraltar sill. Our analyses furthermore show that precessional changes in the freshwater budget may explain the observed cyclic lithological changes of gypsum and non-evaporitic sediments. Potential precipitation of gypsum in the deep Mediterranean basins would have critically depended on the availability of oxygen and thus on the stratification of the water column. Finally, our results indicate that the deep Mediterranean halite units could have been deposited under shallow conditions, assuming that they correspond to the ~ 70 kyr time interval between glacials TG12 and TG14, when Mediterranean outflow to the Atlantic was blocked.     

Upwelling into the thermocline of the Pacific Ocean

The established “island rule” and the recently introduced “separation formula” are combined to yield an analytical expression for the total upwelling into the thermocline in the Pacific. The combination of the two is achieved with the use of a hybrid model containing a stratified upper layer, a thick (slowly moving) homogenous intermediate layer and an inert lower layer. Both the upper and the intermediate layers are subject to diabatic cooling and heating (which need not be specified) and there is an exchange of mass between the two active layers. An attempt is made to examine the above analytical (hybrid) model numerically. Ideally, this should be done with a complete two-and-a-half layer model (with upwelling and downwelling), but such a model is much too complex for process-oriented studies (due to the required parameterization of vertical mixing). Consequently, we focus our attention on verifying that the separation formula and the island rule are consistent with each other in a much simpler, layer-and-a-half model (without upwelling). We first verified that the new “separation formula” provides a reasonable estimate of the wind-induced transport in an island-free basin. We then compare the wind-induced transport predicted by the separation formula and the island rule in an idealized basin containing an island. We show that in these idealized situations the two methods give results that are consistent with each other and the numerics. We then turned to an application of the (hybrid) two-and-a-half layer model to the Pacific where, in contrast to the idealized layer-and-a-half models (where the two methods address the same water mass), the two methods address two different water masses. While the separation formula addresses only thermocline water (σ_θ<26.20), the island rule addresses all the water down to 27.5σ_θ (i.e., both the upper and intermediate layer). This is why the application of the two methods to the Pacific gives two different results — an application of the formula gives zero warm water transport whereas an application of the island rule gives 16 Sv. Namely, the difference between the amount predicted by the island rule (16 Sv) and the amount predicted by the separation formula (zero) enters the Pacific as intermediate water and is then somehow upwelled into the thermocline. The upwelling should take place north of the southern western boundary currents separation (40°S).     

An experimental method for determining the frequency-dependent added mass and added mass moment of inertia for a floating body in heave and pitch motions

Most of the existing relevant materials have been obtained from experiments, in which evaluating the added mass at the resonant frequency corresponding to the peak of a frequency-response curve obtained from the “forced” vibration analysis is the most popular technique. In this paper, a simple experimental method was presented where the “free” vibration responses instead of the “forced” ones were used to determine the values of m_ah and I_ap. The main part of the experimental system is composed of a floating body (model) and a spring–shaft shaker. The “free” vibration of this main part was induced by imposing on it an initial displacement (and/or an initial velocity), and from the time histories of displacements information such as the “damped” natural frequencies, damping ratios, sectional added mass coefficients (C_V and C_P) were obtained. Since the displacements of the spring–shaft shaker are “translational” and those of the floating body due to pitch motions are “angular”, a technique for the transformation between the associated parameters of the two components of the main part was presented.     

A turbidity survey of Narragansett Bay

A turbidity survey of Narragansett Bay, Rhode Island, was made during the summer months of 1971 and included measurements of the attenuation function for scalar irradiance for daylight and the volume attenuation function for white tungsten light at various depths. One hundred and three stations were made at 17 different locations. Variations in the optical parameters were large, one standard deviation at any given location ranging from 7 to 23 per cent of the mean value. This variation was only slightly dependent on the state of the tidal currents, depth of the location, or weather factors. The magnitude of turbidity variations was almost 4-fold over a north-south range of 31 km within the estuary, with clearest water at the southern mouths of the Bay. A good correlation exists between turbidity parameters and Autumn values of suspended-material concentration found by Morton (1967), with both data sets showing highest turbidity and suspended concentrations in the West Passage of the Bay. “Wedges” and “bulges” of clear water were detected throughout the Bay but were most evident at the southern (Atlantic Ocean) end.Although it was not possible to fully define the parameters producing these temporal and geographic variations in estuarine turbidity, it is suggested that knowledge of these parameters can assist those concerned with the physical and biological state of an estuary, as well as divers and photographers plying their trades within its boundaries.     

Tracking the last sea-level cycle: seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf

Seafloor geomorphology and surficial stratigraphy of the New Jersey middle continental shelf provide a detailed record of sea-level change during the last advance and retreat of the Laurentide ice sheet (120 kyr B.P. to Present). A NW–SE-oriented corridor on the middle shelf between water depths of 40 m (the mid-shelf “paleo-shore”) and 100 m (the Franklin “paleo-shore”) encompasses 500 line-km of 2D Huntec boomer profiles (500–3500 Hz), an embedded 4.6 km² 3D volume, and a 490 km² swath bathymetry map. We use these data to develop a relative stratigraphy. Core samples from published studies also provide some chronological and sedimentological constraints on the upper <5 m of the stratigraphic succession.The following stratigraphic units and surfaces occur (from bottom to top): (1) “R”, a high-amplitude reflection that separates sediment >46.5 kyr old (by AMS ¹⁴C dating) from overlying sediment wedges; (2) the outer shelf wedge, a marine unit up to 50 m thick that onlaps “R”; (3) “Channels”, a reflection sub-parallel to the seafloor that incises “R”, and appears as a dendritic system of channels in map view; (4) “Channels” fill, the upper portion of which is sampled and known to represent deepening-upward marine sediments 12.3 kyr in age; (5) the “T” horizon, a seismically discontinuous surface that caps “Channels” fill; (6) oblique ridge deposits, coarse-grained shelly units comprised of km-scale, shallow shelf bedforms; and (7) ribbon-floored swales, bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits.We interpret this succession of features in light of a global eustatic sea-level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr. The morphology of the New Jersey middle shelf shows a discrete sequence of stratigraphic elements, and reflects the pulsed episodicity of the last sea-level cycle. “R” is a complicated marine/non-marine erosional surface formed during the last regression, while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum Wisconsin lowstand (i.e., marine oxygen isotope stage 3.1). “Channels” is a widespread fluvial subarial erosion surface formed at the late Wisconsin glacial maximum 22 kyr B.P. The shoreline migrated back across the mid-shelf corridor non-uniformly during the period represented by “Channels” fill. Oblique ridges are relict features on the New Jersey middle shelf, while the ribbon-floored swales represent modern shelf erosion. There is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession.     

Total (practical) stability of ships

In this paper the “total (practical) stability” concept is introduced to nonlinear forced rolling motion of a ship. This is achieved by employing “boundedness” and “Lyapunov's function” approach. In this respect two new theorems are proved and conditions and domain of Practical Stability are evaluated. The Paper also contains a critical review of the present status of international intact ship stability regulations. A qualitative discussion of oscillatory rolling motion and the capsizing phenomena is presented.     

Alternative placement technique for antifer blocks used on breakwaters

In this study, a placement technique named as “alternative placement technique” was developed for antifer blocks and the results of its application to a breakwater model were presented. This placement technique was compared with the existing techniques such as the “regular placement technique”, the “irregular placement technique” and the “sloped wall placement technique” by experiments. The comparison was carried out considering armor layer stability, prototype placement, clarity of the placement technique’s definition, armor layer cost, and wave runup. As a result of this investigation the “alternative placement technique” was found to be superior to the other existing placement techniques.     

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.     

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.     

Assessment of water exchange between a discharge region and the open sea – A comparison of different methodological concepts

Two different methods of estimating the water exchange through the Baltic coastal region of Laxemar have been used, consisting of particle trajectories and passive tracers. Water is traced from and to a small discharge region near the coast. The discharge material in this region is treated as zero-dimensional particles or tracers with neutral buoyancy. The real discharge material could be a leakage of radio-nuclides through the sea floor from an underground repository of nuclear waste.Water exchange rates between the discharge region and the model domain are estimated using both forward and backward trajectories as well as passive tracers. The Lagrangian trajectories can account for the time evolution of the water exchange while the tracers give one average age per model grid box. Water exchange times such as residence time, age and transient times have been calculated with trajectories but only the average age (AvA) for tracers. The trajectory calculations provide a more detailed time evolution than the tracers.On the other hand the tracers are integrated “on-line” simultaneously in the sea circulation model with the same time step while the Lagrangian trajectories are integrated “off-line” from the stored model velocities with its inherent temporal resolution, presently 1 h. The sub-grid turbulence is parameterised as the Laplacian diffusion for the passive tracers and with an extra stochastic velocity for trajectories. The importance of the parameterised sub-grid turbulence for the trajectories is estimated to give an extra diffusion of the same order as the Laplacian diffusion by comparing the Lagrangian dispersions with and without parameterisation. The results of the different methods are similar but depend on the chosen diffusivity coefficient with a slightly higher correlation between trajectories and tracers when integrated with a lower diffusivity coefficient.