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58-496: Littoral zone is an area near the coastline of a body of water. Littoral or Litoral may also refer to: Littoral zone The word littoral may be used both as a noun and as an adjective . It derives from the Latin noun litus, litoris , meaning "shore". (The doubled t is a late-medieval innovation, and the word is sometimes seen in the more classical-looking spelling litoral .) The term has no single definition. What

116-455: A chlorophyll maximum layer. These layers in turn attract large aggregations of mobile zooplankton that internal bores subsequently push inshore. Many taxa can be almost absent in warm surface waters, yet plentiful in these internal bores. While internal waves of higher magnitudes will often break after crossing over the shelf break, smaller trains will proceed across the shelf unbroken. At low wind speeds these internal waves are evidenced by

174-545: A broad littoral zone to a narrow band of vegetation. Marshes and wet meadows are at particular risk. For the purposes of naval operations, the US Navy divides the littoral zone in the ways shown on the diagram at the top of this article. The US Army Corps of Engineers and the US Environmental Protection Agency have their own definitions, which have legal implications. The UK Ministry of Defence defines

232-550: A constant, is the characteristic ambient density. Solving the four equations in four unknowns for a wave of the form exp ⁡ [ i ( k x + m z − ω t ) ] {\displaystyle \exp[i(kx+mz-\omega t)]} gives the dispersion relation in which N {\displaystyle N} is the buoyancy frequency and Θ = tan − 1 ⁡ ( m / k ) {\displaystyle \Theta =\tan ^{-1}(m/k)}

290-426: A continuously stratified medium may propagate vertically as well as horizontally. The dispersion relation for such waves is curious: For a freely-propagating internal wave packet , the direction of propagation of energy ( group velocity ) is perpendicular to the direction of propagation of wave crests and troughs ( phase velocity ). An internal wave may also become confined to a finite region of altitude or depth, as

348-404: A fluid parcel of density ρ {\displaystyle \rho } surrounded by an ambient fluid of density ρ 0 {\displaystyle \rho _{0}} . Its weight per unit volume is g ( ρ − ρ 0 ) {\displaystyle g(\rho -\rho _{0})} , in which g {\displaystyle g}

406-423: A greater variety of plant and animal life, and particularly the formation of extensive wetlands . In addition, the additional local humidity due to evaporation usually creates a microclimate supporting unique types of organisms. In oceanography and marine biology , the idea of the littoral zone is extended roughly to the edge of the continental shelf . Starting from the shoreline, the littoral zone begins at

464-603: A layer of relatively fresh water whose depth is comparable to the ship's draft. This causes a wake of internal waves that dissipates a huge amount of energy. Internal waves typically have much lower frequencies and higher amplitudes than surface gravity waves because the density differences (and therefore the restoring forces) within a fluid are usually much smaller. Wavelengths vary from centimetres to kilometres with periods of seconds to hours respectively. The atmosphere and ocean are continuously stratified: potential density generally increases steadily downward. Internal waves in

522-405: A narrow or broad fringing wetland, with extensive areas of aquatic plants sorted by their tolerance to different water depths. Typically, four zones are recognized, from higher to lower on the shore: wooded wetland, wet meadow , marsh and aquatic vegetation . The relative areas of these four types depends not only on the profile of the shoreline, but upon past water levels. The area of wet meadow

580-426: A result of varying stratification or wind . Here, the wave is said to be ducted or trapped , and a vertically standing wave may form, where the vertical component of group velocity approaches zero. A ducted internal wave mode may propagate horizontally, with parallel group and phase velocity vectors , analogous to propagation within a waveguide . At large scales, internal waves are influenced both by

638-408: A second-order ordinary differential equation in z {\displaystyle z} . Insisting on bounded solutions the velocity potential in each layer is and with A {\displaystyle A} the amplitude of the wave and ω {\displaystyle \omega } its angular frequency . In deriving this structure, matching conditions have been used at

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696-768: A shelf break. The largest of these waves are generated during springtides and those of sufficient magnitude break and progress across the shelf as bores. These bores are evidenced by rapid, step-like changes in temperature and salinity with depth, the abrupt onset of upslope flows near the bottom and packets of high frequency internal waves following the fronts of the bores. The arrival of cool, formerly deep water associated with internal bores into warm, shallower waters corresponds with drastic increases in phytoplankton and zooplankton concentrations and changes in plankter species abundances. Additionally, while both surface waters and those at depth tend to have relatively low primary productivity, thermoclines are often associated with

754-544: A slab of fluid with uniform density ρ 2 {\displaystyle \rho _{2}} . Arbitrarily the interface between the two layers is taken to be situated at z = 0. {\displaystyle z=0.} The fluid in the upper and lower layers are assumed to be irrotational . So the velocity in each layer is given by the gradient of a velocity potential , u → = ∇ ϕ , {\displaystyle {{\vec {u}}=\nabla \phi ,}} and

812-674: A small amount (the Boussinesq approximation ). Assuming the waves are two dimensional in the x-z plane, the respective equations are in which ρ {\displaystyle \rho } is the perturbation density, p {\displaystyle p} is the pressure, and ( u , w ) {\displaystyle (u,w)} is the velocity. The ambient density changes linearly with height as given by ρ 0 ( z ) {\displaystyle \rho _{0}(z)} and ρ 00 {\displaystyle \rho _{00}} ,

870-466: A small fraction of total lake areas. Because the littoral zone is important for many recreational and industrial purposes, it is often severely affected by many human activities that increase nutrient loading, spread invasive species, cause acidification and climate change , and produce increased fluctuations in water level. Littoral zones are both more negatively affected by human activity and less intensively studied than offshore waters. Conservation of

928-552: A train of internal waves can be visualized by rippled cloud patterns described as herringbone sky or mackerel sky . The outflow of cold air from a thunderstorm can launch large amplitude internal solitary waves at an atmospheric inversion . In northern Australia, these result in Morning Glory clouds , used by some daredevils to glide along like a surfer riding an ocean wave. Satellites over Australia and elsewhere reveal these waves can span many hundreds of kilometers. Undulations of

986-580: A water column is in hydrostatic equilibrium and a small parcel of fluid with density ρ 0 ( z 0 ) {\displaystyle \rho _{0}(z_{0})} is displaced vertically by a small distance Δ z {\displaystyle \Delta z} . The buoyant restoring force results in a vertical acceleration, given by This is the spring equation whose solution predicts oscillatory vertical displacement about z 0 {\displaystyle z_{0}} in time about with frequency given by

1044-526: A wider extension and are often divided into further zones. For more on this, see intertidal ecology . The sublittoral zone starts immediately below the eulittoral zone. This zone is permanently covered with seawater and is approximately equivalent to the neritic zone . In physical oceanography , the sublittoral zone refers to coastal regions with significant tidal flows and energy dissipation, including non-linear flows, internal waves , river outflows and oceanic fronts. In practice, this typically extends to

1102-415: Is much more dense than air, the displacement of water by air from a surface gravity wave feels nearly the full force of gravity ( g ′ ∼ g {\displaystyle g^{\prime }\sim g} ). The displacement of the thermocline of a lake, which separates warmer surface from cooler deep water, feels the buoyancy force expressed through the reduced gravity. For example,

1160-457: Is often attracted to shorelines, and settlement often disrupts breeding habitats for littoral zone species. For example, many turtles are killed on roads when they leave the water to lay their eggs in upland sites. Fish can be negatively affected by docks and retaining walls which remove breeding habitat in shallow water. Some shoreline communities even deliberately try to remove wetlands since they may interfere with activities like swimming. Overall,

1218-497: Is particularly dependent upon past water levels; in general, the area of wet meadows along lakes and rivers increases with natural water level fluctuations. Many of the animals in lakes and rivers are dependent upon the wetlands of littoral zones, since the rooted plants provide habitat and food. Hence, a large and productive littoral zone is considered an important characteristic of a healthy lake or river. Littoral zones are at particular risk for two reasons. First, human settlement

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1276-469: Is regarded as the full extent of the littoral zone, and the way the littoral zone is divided into subregions, varies in different contexts. For lakes, the littoral zone is the nearshore habitat where photosynthetically active radiation penetrates to the lake bottom in sufficient quantities to support photosynthesis. The use of the term also varies from one part of the world to another, and between different disciplines. For example, military commanders speak of

1334-488: Is the acceleration of gravity. Dividing by a characteristic density, ρ 00 {\displaystyle \rho _{00}} , gives the definition of the reduced gravity: If ρ > ρ 0 {\displaystyle \rho >\rho _{0}} , g ′ {\displaystyle g^{\prime }} is positive though generally much smaller than g {\displaystyle g} . Because water

1392-425: Is the angle of the wavenumber vector to the horizontal, which is also the angle formed by lines of constant phase to the vertical. The phase velocity and group velocity found from the dispersion relation predict the unusual property that they are perpendicular and that the vertical components of the phase and group velocities have opposite sign: if a wavepacket moves upward to the right, the crests move downward to

1450-430: Is the same as that for deep water surface waves by setting g ′ = g . {\displaystyle g^{\prime }=g.} The structure and dispersion relation of internal waves in a uniformly stratified fluid is found through the solution of the linearized conservation of mass, momentum, and internal energy equations assuming the fluid is incompressible and the background density varies by

1508-461: Is typically little surface expression of the waves, aside from slick bands that can form over the trough of the waves. Internal waves are the source of a curious phenomenon called dead water , first reported in 1893 by the Norwegian oceanographer Fridtjof Nansen , in which a boat may experience strong resistance to forward motion in apparently calm conditions. This occurs when the ship is sailing on

1566-530: The Minnesota Department of Natural Resources defines littoral as that portion of the lake that is less than 15 feet in depth. Such fixed-depth definitions often do not accurately represent the true ecological zonation, but are sometimes used because they are simple measurements to make bathymetric maps or when there are no measurements of light penetration. The littoral zone comprises an estimated 78% of Earth's total lake area. The littoral zone may form

1624-467: The buoyancy frequency : The above argument can be generalized to predict the frequency, ω {\displaystyle \omega } , of a fluid parcel that oscillates along a line at an angle Θ {\displaystyle \Theta } to the vertical: This is one way to write the dispersion relation for internal waves whose lines of constant phase lie at an angle Θ {\displaystyle \Theta } to

1682-491: The area above the spring high tide line that is regularly splashed, but not submerged by ocean water. Seawater penetrates these elevated areas only during storms with high tides. Organisms that live here must cope with exposure to fresh water from rain, cold, heat, dryness and predation by land animals and seabirds. At the top of this area, patches of dark lichens can appear as crusts on rocks. Some types of periwinkles , Neritidae and detritus feeding Isopoda commonly inhabit

1740-543: The atmosphere where substantial changes in air density influences their dynamics, they are called anelastic (internal) waves. If generated by flow over topography, they are called Lee waves or mountain waves . If the mountain waves break aloft, they can result in strong warm winds at the ground known as Chinook winds (in North America) or Foehn winds (in Europe). If generated in the ocean by tidal flow over submarine ridges or

1798-535: The continental shelf, they are called internal tides. If they evolve slowly compared to the Earth's rotational frequency so that their dynamics are influenced by the Coriolis effect , they are called inertia gravity waves or, simply, inertial waves . Internal waves are usually distinguished from Rossby waves , which are influenced by the change of Coriolis frequency with latitude. An internal wave can readily be observed in

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1856-407: The density changes over a small vertical distance (as in the case of the thermocline in lakes and oceans or an atmospheric inversion ), the waves propagate horizontally like surface waves, but do so at slower speeds as determined by the density difference of the fluid below and above the interface. If the density changes continuously, the waves can propagate vertically as well as horizontally through

1914-573: The density difference between ice water and room temperature water is 0.002 the characteristic density of water. So the reduced gravity is 0.2% that of gravity. It is for this reason that internal waves move in slow-motion relative to surface waves. Whereas the reduced gravity is the key variable describing buoyancy for interfacial internal waves, a different quantity is used to describe buoyancy in continuously stratified fluid whose density varies with height as ρ 0 ( z ) {\displaystyle \rho _{0}(z)} . Suppose

1972-426: The edge of the continental shelf , with depths around 200 meters. In marine biology, the sublittoral zone refers to the areas where sunlight reaches the ocean floor, that is, where the water is never so deep as to take it out of the photic zone . This results in high primary production and makes the sublittoral zone the location of the majority of sea life. As in physical oceanography, this zone typically extends to

2030-423: The edge of the continental shelf . The benthic zone in the sublittoral is much more stable than in the intertidal zone; temperature, water pressure, and the amount of sunlight remain fairly constant. Sublittoral corals do not have to deal with as much change as intertidal corals. Corals can live in both zones, but they are more common in the sublittoral zone. Within the sublittoral, marine biologists also identify

2088-430: The exchange of water between coastal and offshore environments, is of particular interest for its role in delivering meroplanktonic larvae to often disparate adult populations from shared offshore larval pools. Several mechanisms have been proposed for the cross-shelf of planktonic larvae by internal waves. The prevalence of each type of event depends on a variety of factors including bottom topography, stratification of

2146-488: The fluid. Internal waves, also called internal gravity waves, go by many other names depending upon the fluid stratification, generation mechanism, amplitude, and influence of external forces. If propagating horizontally along an interface where the density rapidly decreases with height, they are specifically called interfacial (internal) waves. If the interfacial waves are large amplitude they are called internal solitary waves or internal solitons . If moving vertically through

2204-420: The following: Shallower regions of the sublittoral zone, extending not far from the shore, are sometimes referred to as the subtidal zone . Many vertebrates (e.g., mammals, waterfowl, reptiles) and invertebrates (insects, etc.) use both the littoral zone as well as the terrestrial ecosystem for food and habitat. Biota that are commonly assumed to reside in the pelagic zone often rely heavily on resources from

2262-518: The formation of wide surface slicks, oriented parallel to the bottom topography, which progress shoreward with the internal waves. Waters above an internal wave converge and sink in its trough and upwell and diverge over its crest. The convergence zones associated with internal wave troughs often accumulate oils and flotsam that occasionally progress shoreward with the slicks. These rafts of flotsam can also harbor high concentrations of larvae of invertebrates and fish an order of magnitude higher than

2320-447: The interface requiring continuity of mass and pressure. These conditions also give the dispersion relation : in which the reduced gravity g ′ {\displaystyle g^{\prime }} is based on the density difference between the upper and lower layers: with g {\displaystyle g} the Earth's gravity . Note that the dispersion relation

2378-510: The kitchen by slowly tilting back and forth a bottle of salad dressing - the waves exist at the interface between oil and vinegar. Atmospheric internal waves can be visualized by wave clouds : at the wave crests air rises and cools in the relatively lower pressure, which can result in water vapor condensation if the relative humidity is close to 100%. Clouds that reveal internal waves launched by flow over hills are called lenticular clouds because of their lens-like appearance. Less dramatically,

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2436-462: The littoral as those land areas (and their adjacent areas and associated air space) that are susceptible to engagement and influence from the sea . Internal wave Internal waves are gravity waves that oscillate within a fluid medium, rather than on its surface. To exist, the fluid must be stratified : the density must change (continuously or discontinuously) with depth/height due to changes, for example, in temperature and/or salinity. If

2494-437: The littoral in ways that are quite different from the definition used by marine biologists . The adjacency of water gives a number of distinctive characteristics to littoral regions. The erosive power of water results in particular types of landforms , such as sand dunes , and estuaries . The natural movement of the littoral along the coast is called the littoral drift . Biologically, the ready availability of water enables

2552-419: The littoral zone. Littoral areas of ponds and lakes are typically better oxygenated, structurally more complex, and afford more abundant and diverse food resources than do profundal sediments. All these factors lead to a high diversity of insects and very complex trophic interactions. The great lakes of the world represent a global heritage of surface freshwater and aquatic biodiversity. Species lists for 14 of

2610-401: The lower supralittoral. The eulittoral zone (also called the midlittoral or mediolittoral zone ) is the intertidal zone , known also as the foreshore . It extends from the spring high tide line, which is rarely inundated, to the spring low tide line, which is rarely not inundated. It is alternately exposed and submerged once or twice daily. Organisms living here must be able to withstand

2668-487: The oceanic thermocline can be visualized by satellite because the waves increase the surface roughness where the horizontal flow converges, and this increases the scattering of sunlight (as in the image at the top of this page showing of waves generated by tidal flow through the Strait of Gibraltar ). According to Archimedes principle , the weight of an immersed object is reduced by the weight of fluid it displaces. This holds for

2726-401: The periodic influx of high phytoplankton concentrations. Periodic depression of the thermocline and associated downwelling may also play an important role in the vertical transport of planktonic larvae. Large steep internal waves containing trapped, reverse-oscillating cores can also transport parcels of water shoreward. These non-linear waves with trapped cores had previously been observed in

2784-401: The potential itself satisfies Laplace's equation : Assuming the domain is unbounded and two-dimensional (in the x − z {\displaystyle x-z} plane), and assuming the wave is periodic in x {\displaystyle x} with wavenumber k > 0 , {\displaystyle k>0,} the equations in each layer reduces to

2842-420: The presence of human settlement has a demonstrated negative impact upon adjoining wetlands. An equally serious problem is the tendency to stabilize lake or river levels with dams. Dams removed the spring flood, which carries nutrients into littoral zones and reduces the natural fluctuation of water levels upon which many wetland plants and animals depend. Hence, over time, dams can reduce the area of wetland from

2900-484: The remarkable biodiversity and biotic integrity of large lakes will require better integration of littoral zones into our understanding of lake ecosystem functioning and focused efforts to alleviate human impacts along the shoreline. In freshwater situations, the littoral zone is the nearshore habitat where photosynthetically active radiation penetrates to the lake bottom in sufficient quantities to support photosynthesis. Sometimes other definitions are used. For example,

2958-407: The right. Most people think of waves as a surface phenomenon, which acts between water (as in lakes or oceans) and the air. Where low density water overlies high density water in the ocean , internal waves propagate along the boundary. They are especially common over the continental shelf regions of the world oceans and where brackish water overlies salt water at the outlet of large rivers. There

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3016-744: The rotation of the Earth as well as by the stratification of the medium. The frequencies of these geophysical wave motions vary from a lower limit of the Coriolis frequency ( inertial motions ) up to the Brunt–Väisälä frequency , or buoyancy frequency (buoyancy oscillations). Above the Brunt–Väisälä frequency , there may be evanescent internal wave motions, for example those resulting from partial reflection . Internal waves at tidal frequencies are produced by tidal flow over topography/bathymetry, and are known as internal tides . Similarly, atmospheric tides arise from, for example, non-uniform solar heating associated with diurnal motion . Cross-shelf transport,

3074-399: The spray region just above the high tide mark. From here, it moves to the intertidal region between the high and low water marks, and then out as far as the edge of the continental shelf . These three subregions are called, in order, the supralittoral zone , the eulittoral zone , and the sublittoral zone . The supralittoral zone (also called the splash , spray or supratidal zone ) is

3132-406: The surrounding waters. Thermoclines are often associated with chlorophyll maximum layers. Internal waves represent oscillations of these thermoclines and therefore have the potential to transfer these phytoplankton rich waters downward, coupling benthic and pelagic systems. Areas affected by these events show higher growth rates of suspension feeding ascidians and bryozoans , likely due to

3190-411: The varying conditions of temperature, light, and salinity. Despite this, productivity is high in this zone. The wave action and turbulence of recurring tides shape and reform cliffs, gaps and caves, offering a huge range of habitats for sedentary organisms. Protected rocky shorelines usually show a narrow, almost homogenous, eulittoral strip, often marked by the presence of barnacles . Exposed sites show

3248-470: The vertical. In particular, this shows that the buoyancy frequency is an upper limit of allowed internal wave frequencies. The theory for internal waves differs in the description of interfacial waves and vertically propagating internal waves. These are treated separately below. In the simplest case, one considers a two-layer fluid in which a slab of fluid with uniform density ρ 1 {\displaystyle \rho _{1}} overlies

3306-495: The water body, and tidal influences. Similarly to surface waves, internal waves change as they approach the shore. As the ratio of wave amplitude to water depth becomes such that the wave “feels the bottom,” water at the base of the wave slows down due to friction with the sea floor. This causes the wave to become asymmetrical and the face of the wave to steepen, and finally the wave will break, propagating forward as an internal bore. Internal waves are often formed as tides pass over

3364-416: The world's largest lakes reveal that 15% of the global diversity (the total number of species) of freshwater fishes, 9% of non-insect freshwater invertebrate diversity, and 2% of aquatic insect diversity live in this handful of lakes. The vast majority (more than 93%) of species inhabit the shallow, nearshore littoral zone, and 72% are completely restricted to the littoral zone, even though littoral habitats are

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