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Exam 2 Notes

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PROPERTIES OF SEAWATER
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High specific heat capacity
High solvent power, “universal solvent”
Covalent bonding
Asymmetry of covalent bond => dipole structure, hydrogen bonding – higher than
expected melting/boiling points, high heat capacity of water directly related to hydrogen
bonding, dipole structure
Density (as a solid) – Hydrogen bonding causes hexagonal shape to form when water
freezes- angle of separation between the hydrogen atoms widens, making ice less dense
than water.
Cation- positively charged ion
Anion- negatively charged ionk
Negative end of H2O molecule dislodges cation, positive dislodges anion, dissolution continues
until saturation or halilte has dissolved
Hydration- water molecules keeps ions separated
Polymers- loose aggregates of molecules that resemble the crystalline structure of ice persist
until 3.98 degrees Centigrade. Below this temp, density of water decreases as temp decreases
until it freezes. Above it, the density decreases with increasing temp.
Conservative Ions – major constituents (chloride, sodium, sulfate, magnesium, calcium,
potassium, bicarbonate, bromide, boric acid, strontium, and fluoride) very little over time
NUTRIENTS
Nutrients in seawater – Nitrogen, Phosphorous, Silicon
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Silicon used to make shells around diatoms/radiolaria
Seawater nutrients vary greatly compared to the conservative ions- non-conservative ions
GASES
Noble/Inert gases and rarely involved directly in plant photosynthesis. Non-conservative- levels
of O2/CO2 greatly influenced by photosynthesis/organic respiration.
TRACE ELEMENTS
-Occur in very small concentrations (ppm, ppb, ppt)
-Critically important for marine organisms- either by helping to promote life or by
retarding/killing life (toxicity)
ORGANIC COMPOUNDS
-large, complex molecules
-produced by metabolic and decay processes of organisms
SALINITY
Principle of Constant proportion- ratio of any two major constituents in seawater holds
constant. In theory, allowed salinity to be measured by measuring the amount of a single major
dissolved ion since the ratio would be fixed. Chemists measure ClChlorinity- total quantity of halogens dissolved in water, expressed as g/kg (0/00)
FACTORS THAT REGULATE SALINITY IN SEAWATER
H2O + CO2 yields H2CO3 yields H+ + HCO3When carbon dioxide is dissolved in water, it reacts with water to produce carbonic acid, which
separates into hydrogen and bicarbonate ions.
Steady-state equilibrium – balance between inputs/outputs of salt to the ocean.
Sources/sinks – inputs/outputs of material
Evaporation rates high in warm climates, over time, salinity rises, produces a brine. Leads to
super-saturation, which leads to precipitation of evaporite minerals like halite
(NaCl) and gypsum. This represents a sink
Winds blow onshore large amounts of sea spray, freshly extruded basalt lavas on the ocean floor
react and extract dissolved ions, adsorption (sticking of ions to a surface) of cations like K+ and
SO42- to clay minerals in the ocean, formation of ferromanganese nodules are all sinks of ions
dissolved in seawater.
Organisms help maintain steady-state as well
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Shells created from ions
Hard parts form oozes
Some species extract dissolved substances in seawater, these substances are
concentrated in fecal matter, incorporated in sediment
Salinity of ocean largely due to weathering and erosion of rocks on land
-difference in relative composition of solutes in seawater and river water is a result of the
residence time of ions in the ocean, which is simply the average length of time an ion remains in
solution there. Na and Cl have very long residence times. Can also explain the principle of
constant proportions- rapid mixing and very long residence times ensure uniformity.
-River water doesn’t mirror ocean waters because bicarbonates, calcium, and silica are involved
in biological processes, so are more common in river water and ocean water. Most common ions
in seawater have longest residence time
EFFECTS OF SALINITY ON WATER PROPERTIES
Lower freezing point – salt ions disrupt rearrangement of water molecules into ice crystal
Density increases with salinity
Vapor pressure – pressure exerted by a liquid’s own vapor when in a container at equilibrium.
As salinity increases, vapor pressure drops (freshwater evaporates at a faster rate than does
seawater) – again, salt ions ‘hold on’ to water molecules and disrupt evaporation
CHEMICAL/PHYSICAL STRUCTURE OF OCEANS
Insolation (solar energy hitting earth’s surface) strongly affected by latitude
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Surface water temps are greater in the tropics and decrease with distance from
equator
Isotherms (imaginary contour lines that connect points of equal water temp) trend parallel to
lines of latitude.
Oceans in the middle and lower latitudes have a layered thermal structure
Thermocline – temperature changes rapidly with depth, sharp gradient.
Salinity of surface water shows clear latitudinal dependence
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Salinity highest between 20 and 30 degrees north and south latitude, and decrease
toward the equator and the poles. Caused by addition/removal of H2O molecules
from seawater.
Evaporation, formation of ice = remove water molecules
Precipitation (rain, snow, sleet), river runoff, ice melting add water molecules
Halocline – sharp salinity gradient
Pycnocline- sharp density gradient
Water stratification – layering of waters, where a lens of high salinity surface water is
separated from less saline water below by a sharp halocline.
It is possible to have high salinity water over low salinity water, provided that the temperature
difference between the waters is large enough that the density of the higher salinity water is
lower than that of the lower salinity water underneath
Surface layer
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2% of ocean’s volume
Averages 100m depth
Light penetrates to bottom of this zone, allowing plant photosynthesis to occur (if
nutrients are adequately abundant)
Least dense water of the water column
In polar regions, cooling of surface waters produces dense water that sinks, which prevents a
pycnocline from forming in these regions.
Pycnocline layer
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18% of ocean’s volume
In low latitudes, corresponds to permanent thermocline created by heating of water by
sun
In midlatitudes, pycnocline weakens and corresponds with the halocline, created by
the rainfall that dilutes salinity of water in the surface layer.
Deep layer
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80% of the ocean’s volume
Mostly originates in high latitudes, where it is cooled while in contact with cold
atmosphere
Sinks to ocean floor
GASES IN SEAWATER
Saturation value- amount of gas at equilibrium that can be dissolved by a volume of water at
specific salinity, temp, and pressure. Higher saturation value is for a gas, the greater its
solubility.
Solubility of gas increases with a drop in either seawater temp or salinity, and a rise in pressure
Concentration of a gas dissolved in 1 liter of 0 degrees C water at 1atm
Surface water is near-saturation with respect to the common atmospheric gases (O2, N2, CO2)
Breaking waves, especially those in storms, drive air bubbles down.
Primary regulator of gas concentrations are organisms. When light and nutrients are sufficient,
photosynthesis will convert water and carbon dioxide, and liberate oxygen. Respiration results
in uptake of O2 and release of CO2 as organisms oxidize food. Dead organic matter and
excrement are decomposed by microbes, which consumes oxygen and releases CO2.
OXYGEN
Vertical distribution of oxygen in low and mid latitudes shows a distinct pattern. Warm surface
water layer with high oxygen content separated from cold, relatively well aerated deep water by
a distinct oxygen-minimum layer.
Sources of oxygen- gas diffusion across air-sea interface, and photosynthesis. Oxygen-minimum
layer coincides with the pycnocline, implying a connection. Organisms are drawn to the
pycnocline due to its food supply, respire, and reduce the 02. This combined with slow mixing,
leads to the oxygen-minimum layer being established at the pycnocline layer. Advection
(horizontal/vertical movement of liquid- in high latitudes, surface water is cooled, raises its
saturation value, sinks due to high density, flow equatorward, ventilating the depths of all the
ocean basins)
CARBON DIOXIDE
Reaction with water yields H+ ions, lower the pH of the water (makes it more acidic)
The CO2 system will react to changes in the system so that an equilibrium is always tended
towards. Example: removal of CO2 by plants during photosynthesis initiates chemical responses
which shift the reaction to the left, producing CO2. Respiration releases CO2 and shifts the
system to the right to increase the proportion of the other chemicals in response to the increase in
CO2.
Buffered solution- pH is hardly affected due to the nature of the CO2 system. Increasing H+ for
example would lower the pH (more acidic) which in turn would remove H+ as it buffers with
HCO3- to form H2CO3 and keeping the pH near original value.
Higher CO2 content = more acidic the water will be (lower the pH will be). High CO2
concentration in deep waters due to high pressure and lower temp which increases saturation
value, leads to acidic deep water that dissolves CaCO3 shells on the deep-sea floor. Shallow
waters have a higher pH, releases CO32- which bond to the abundant Ca2+ and buffer as they
precipitate CaCO3.
Hydrologic cycle- exchange of water among the ocean, atmosphere, and land.
Biochemical recycling of matter- inorganic nutrients converted to food by plant photosynthesis
in the surface-waters, animals eat plants and one another. When plants/animals die, their bodies
settle through the water column, where it is converted into simple nutrients by bacterial
decomposition. This nutritive water is then upwelled to the surface, completing the cycle.
CH 6
AIR PRESSURE
When density of air is lower than normal due to increase in water vapor current or temperature),
low pressure zone occurs. Converse for high pressure zones.
CORIOLIS DEFLECTION
Winds blow in response to pressure gradients on Earth
Uneven distribution of solar radiation causes winds (high solar radiation at equator produces hot
air, low density- rises, creating belt of low pressure air). Air sinks at poles and rises at equators.
Coriolis Effect – effect of earth’s rotation on wind direction
Looking down on earth from north pole- counterclockwise spin
Upward from south pole- clockwise spin
Moving objects relative to the ground experience a deflection to the right in the Northern
Hemisphere and to the left in the southern hemisphere.
Hadley Cells
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Heating at equator warms air, low pressure at surface occurs, rises, cools, loses
moisture, density increases, results in a high pressure zone above the equatorial zone,
winds move poleward in both directions North and South, air becomes very dense
around 30 degrees N and S latitutdes. Much of this air returns to the equator (one
‘cell’), becoming warmer, picking up moisture on the way. Deflected on its way back
due to Coriolis effect.
Ferrel Cells
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Air circulation in the mid-latitudes (30-60 degrees N and S)
At 30 degrees latitude, some descending air travels poleward while the other travels
back in to the Hadley Cell. These winds are deflected by the Coriolis effect to the
right, cause prevailing westerlies. Encounter cold, dense air at around 50 degrees
latitude (polar front). Equatorial-bound winds from the polar cell link up with the
descending currents at the 30 degrees latitude, completing the cell.
Polar Cells
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Upper air going poleward cools, becomes dense, sinks back to the surface at the
poles.
WIND DRAG
Drags surface water molecules through energy transfer by friction
If prolonged, can create waves and currents.
Surface winds blow in response to differential heating across Earth’s surface and Coriolis
deflection, creating zonal wind flow, the movement of air parallel or near-parallel to latitude
lines. These currents are deflected by the continents, causing circulation gyres to develop.
PRESSURE GRADIENTS
-change in pressure across a horizontal distance
-Water piled up in a mound creates high pressure zone, which causes a tendency for the water to
flow down the pressure gradient.
-Can be piled into a mound- gyres usually have higher levels than periphery. Produced by
converging/diverging of currents, as well as Coriolis deflection
CORIOLIS DEFLECTION
-water currents deflected by Earth’s rotation, bending to the right in the N. Hem and left in the S.
Hem.
-Water currents consequently flow at an angle down pressure gradients, similar to global winds.
TYPES OF SURFACE FLOWS
Ekman spiral- collision of air molecules with water molecules causes water current. Water
molecules on top exert frictional drag on water molecules beneath them, but in a deflected
direction due Coriolis deflection.
Ekman transport- (net water transport due to Coriolis) Ekman transport will be ninety degrees
to the right in N. Hem, to left in S. Hem
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Wind that’s close to shore going to the north along the coast, then Ekman transport
will be ninety degrees to the right, will cause downwelling.
Langmuir Circulation- when wind blows more strongly than about 3.5m/sec, water flows
parallel to the wind. The current motion becomes complex and resembles a corkscrew. Shortterm response to wind (several minutes- several hours), Ekman is long term (several hours to a
few days)
GEOSTROPHIC FLOW
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In N. Hem, westerlies/trade winds induce Ekman transport, which causes water to
flow towards the center of the ocean. Converging flow produces mounds, which has a
pressure gradient. As water begins to flow outward, Coriolis deflection causes the
current to bend to the right. Eventually a stable flow pattern (geostrophic current)
establishes a balance between the pressure gradient and the Coriolis deflection. This
creates a circulation gyre with currents that flow clockwise around the mound of
water. In the southern hemisphere, the geostrophic currents rotate counterclockwise
since Coriolis deflection is to the left.
Western-boundary intensification- swift flow associated with the western arm of all ocean
gyres, irrespective of hemisphere.
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Requires that the tilt of the water slope is steeper on the western than on the eastern
side, since the Coriolis effect’s magnitude is directly related to speed of the current,
and thus the faster the current, the more pronounced gradient and the steeper the
slope.
Steep slope- narrow, deep, strong currents
Gentle slope- broad, shallow, weak currents
Coriolis Effect increases with distance from the equator, which is why eastward-flowing ocean
currents beneath the westerly winds in the Northern Hemisphere turn to the south much more
strongly and quickly than the westward-flowing currents beneath trade winds in the Southern
Hemisphere turn to the north.
Vorticity- amount of circular rotation about a vertical axis that parcels of water undergo because
of planetary spin and current shear. Controls western-boundary intensification in a direct way.
Warm- core rings- clockwise rings
Cold-core rings- counter-clockwise rings
Thermohaline circulation- deep water currents. Arise from density differences due to salinity
and temperature.
Circulation in the Mediterranean Sea
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Evaporation exceeds precipitation and river runoff combined. Warm, salty water
sinks due to high density, filling the deeps, spilling over Gibraltar into N Atlantic.
This water is replaced by surface inflow of seawater from N. Atlantic. Nutrients are
transported out of the photic zone by the downwelling.
Circulation in the Black Sea
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Precipitation and river runoff exceed evaporation. Salinity is low at surface water, this
surface layer is separated by a sharp halocline. Surface water sharply isolated from
deep water, isolated from contact with the surface. Surface water has lots of oxygen,
decomposition of plant matter in the deep waters means a drastically lower oxygen
level. Sharp halocline doesn’t allow the water to turn over, and thus prevents oxygen
renewal at depth. Anoxia (water concentration essentially zero) – below 200m in the
Black Sea. As oxygen disappears with depth, a highly toxic gas, hydrogen sulfide,
appears, produced by anaerobic bacteria. This toxic gas kills life in the surface water
due to frequent mixing
CH 7
WAVES
Capillary-chop-swell-seiche-tsunami-tide
(Ordered by period length)
Waves begin in confused areas called the fetch
Fully developed sea- wave size determined by wind speed and nature of the fetch from the ‘old
sea’
WAVE MOTIONS
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Wind-generated waves are progressive waves because they travel across the sea
surface.
Wave energy, not water particles, travel across the sea surface.
Wave base is ½ wave length (1/2L). Wave-induced motion ceases at this point.
Water depth greater than or equal to 1/2L = deep water wave
Water depth between ½ and 1/20 wavelength = intermediate wave
Water depth less than 1/20 wavelength = shallow water wave
C = L/T, where C= celerity (speed), L is wavelength, and T is wave period. DEEP WAVE
SPEED
Wave speed in m/sec = 1.25sqrt (L)
C = 3.13sqrt (d) m/sec – SHALLOW WATER WAVE SPEED
At the front of a group of waves created by wind, the front wave will die as it expands energy to
set the undisturbed water in motion. However, the water-particle orbits set in motion will
propagate waves behind it. Wave group (wave energy) travels across the surface at a speed less
than the speed of the individual waves.
Rogue waves- unusually large breaking waves constructed of several large waves that have
merged briefly due to constructive interference.
Dispersion- process of wave separation. After the fetch period is over, each of the waves will
separate into a regular swell, since longer waves travel faster than shorter ones. Constructive int.
and destructive interference will occur, resulting in complex, irregular wave form (fetch) from
the interaction of regular waves.
SHALLOW WATER WAVES
Wave Refraction- bending of the wave crest in response to changes in wave speed. Usually, the
crests of waves aren’t exactly parallel to the shore, the crestline lies at some angle and so the
water depth along the crest varies. Different parts of the same crest travel towards shore at
different speeds, dependent upon depth
Wave rays/orthogonals – imaginary arrows drawn perpendicular to the wave crests that divide
an unrefracted wave into equal crestal segments.
SHORE BREAKERS
Steepness = Height/Length, when that’s equal to about 1/7, the wave breaks. At this point, the
crest is over steepened and unstable, and bottom friction makes the bottom of the wave move
slower, so the wave falls over.
Type of breaker determined by steepness of surf zone.
Very steep bottom- surging breaker- waves do not break, instead they move smoothly up and
then down the face of the beach, reflecting much energy seaward. Never attains critical wave
steepness.
Steep – plunging breaker- entire wave front steepens, curls, and collapses, releasing most of its
energy simultaneously.
Relatively flat – spilling breaker – upper part of crest over steepens and spills down the front
side of the wave, continually breaking and slowly losing its energy
SHORELINE UNDER STORM CONDITIONS
Storm Surges- sudden change in coastal water levels produced by storms. Most severe when
coinciding with spring tides. Lead to flooding of low lying coastal areas, contribute to overwash
of barrier islands. Can contribute to the formation of tidal inlets due to the fragmentation of
barrier islands.
Standing waves- remain stationary, oscillate about a node. Maximum vertical displacement
occurs at the antinodes of the wave.
Period in a container for a standing wave = 2L sqrt (gd) sec, where L is the length of the
container
Seiche – standing wave in a lake, harbor, or estuary. When wind dies after a storm, waves slosh
back and forth and can create a seiche. Can become dangerous under conditions that produce
resonance, whenever the period of the force that stacks the water equals the natural period of
oscillation of the basin.
Internal waves- underwater wave, moves along the pycnocline (surfaces that separate water into
different densities).
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Apparently caused by tidal movement of water over an uneven bottom can cause flow
instability and create waves along pycnoclines. Also, friction from one water mass
slipping over another is sometimes enough to cause internal waves.
Tsunami-
Waves are usually shallow-water waves for entire life except over trenches.
CH 8
TIDES
CHARACTERISTICS
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Tidal Range- difference between highest mark and lowest mark due to tides
Tides are single waves that stretch across ocean basins. Behave as shallow water
waves because their wavelengths greatly exceed the depth of the ocean
Diurnal- one high tide, one low
Semidiurnal- two highs and two lows
Mixed- two highs and two lows, but the amplitude from one to the next differs
Strength of gravity varies:
o Inversely as the square of the distance. Directly with masses of interacting
bodies
Spring Tide- when tidal range is at a maximum (highest high and lowest low)
Neap Tide- tidal range is at a minimum
ORIGIN OF TIDES
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Tides, unlike waves, which are driven by wind, are driven by centrifugal force and
gravitational attraction
Strength of gravity varies:
o Inversely as the square of the distance. Directly with masses of interacting
bodies
Moon affects earth more than sun.
Tide producing force varies as distance cubed, so distance matters a lot
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Centrifugal forces arise as earth and moon revolve around common center of mass.
Unequal masses means the center of mass is beneath the earth’s surface,
counteracting the forces of gravitational attraction.
Tidal Bulges
-Centrifugal bulge occurs due to the attraction of the common center of mass between the
Moon and Earth- this is under the Earth’s surface, so the bulge of seawater is away from
the moon as it attempts to correct for this center of mass.
- Gravitational bulge occurs due to the pull of gravity on the earth by the moon. Water is
pulled towards the moon.
-These two bulges form the tides.
Rotary wave- a progressive wave because it progresses around the basin according with the spin
of the Earth.
Amphidromic System- in the northern hemisphere, the tidal bulge created by the tide-raising
forces circulates counter-clockwise around the basin. Once daily for diurnal, twice for
mixed/semidiurnal tides. Water level does not change at the center of the basin, which is a node
referred to as the amphidrophic point. In this way, tides are standing waves.
Cotidal lines- lines on the map that radiate outward from the node of an amphidrophic system
Corange lines- link points of equal tidal ranges
Tidal Bores- a ‘wall’ of water surging upriver with the advancing tide.
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Due to:
Large tidal range greater than 5m, tapering basin geometry, and water depths that
decrease systematically upriver.
Flood Currents- transfer water to the coast, and the tide rises. Ebb currents are the opposite.
Internal tides –when the angle of propogation of internal tides and the gradient of the margin
are equal, internal tidal energy becomes trapped against the seafloor, producing bottom
turbulence.
CH 11
COASTAL PROCESSES
Longshore current- created by the longshore component flow due to the oblique angle of the
incoming wave.
Swash – pushes sand grains at an angle to the beach trend, whereas the returning backwash of
water moves sand straight down the slope of the beach. The result of these interactions is
longshore drift of sand.
The greater the angle of wave approach, the stronger the longshore current will be for the same
wave height.
When wave crests are parallel to the shore, in theory, longshore currents shouldn’t exist.
However, they develop due to wave setup, a process that creates piles of water in the surf zone.
Differing water elevation along the crest can give rise to these currents. They can also come from
wave refraction
Rip Current- if a stretch of shoreline has variable wave setup due to uneven breaker heights, a
nearshore circulation develops. It will consist of a series of diverging and converging longshore
currents. Longshore currents move away from the piles of water due to wave setup, between
these piles, longshore currents converge, and the water is forced to flow out to sea in the rip
current that drains the excess water out of the surf zone.
Excess water is moved parallel to the shore by the longshore currents then flushed out by rip
currents.
BEACHES
Nearshore zone- extends from the breaker zone across the surf zone (where most wave energy
is expanded) to the swash zone (where the beach is constantly covered/uncovered by water with
each wave surge).
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Shifts back and forth as the tide ebbs and floods
Offshore zone – open water that lies seaward of the nearshore zone
Backshore zone- land that adjoins the near-shore zone
BEACH PROFILES
Dunes – formed by wind blowing sand off the dry part of the beach
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Vegetation can influence formation of dunes (salt tolerant, deep root systems, cause
sand to be deposited in their wind shadows)
Saltation- process of sand grain movement across the ground
Sand Spit- tongue of sand created by longshore drift. Other barrier islands seem to have
developed from these. Spit is breached by tidal storms, cutting it off from the mainland.
Barrier islands- large deposits of sand that are separated from the mainland by the water of
estuaries, bays, and lagoons.
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Persistent overwash fans (created by overwash, where large storm waves overtop the
low-lying parts of the Barrier Island and transfer beach and dune sand into the
backshore zone) can move the barrier island landward in response to the rise of sea
level. Bayward side is usually low-energy.
Originated about 5,000 years ago when elongated coastal sand ridges were submerged
during the Holocene rise of sea level. As sea level rose the barriers migrated landward
and the shoreline shifted position
Tidal Inlets- gaps between barrier islands
Erosion at the headlands, embayment on the inlands
Beaches respond to changes in wave energy- bigger waves can erode the beach face and change
its face
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