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INDEX

OCEAN CURRENTS
1. PREFACE
2. CAUSES
3. TYPES
4. SOME IMPORTANT CURRENT
5. IMPORTANCE OF OCEAN CURRENT
6. OCEAN CURRENT AS ALTERNATIVE ENERGY
7. ATLANTIC OCEAN CURRENT
8. PACIFIC OCEAN CURRENT
9. INDIAN OCEAN CURRENT

OCEAN TIDE
1. PREFACE
2. CAUSES
3. TYPES OF TIDE
4. EFFECTS
5. GLOBAL DISTRIBUTION
6. IMPORTANCE
7. REFERENCE
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OCEAN CURRENTS
PREFACE:
Ocean currents are the vertical or horizontal movement of both surface and deep water
throughout the world’s oceans. Currents normally move in a specific direction and aid
significantly in the circulation of the Earth’s moisture, the resultant weather, and water pollution.

Oceanic currents are found all over the globe and vary in size, importance and strength. Some of
the more prominent currents include the California and Humboldt Currents in the Pacific, the
Gulf Stream and Labrador Current in the Atlantic and the Indian Monsoon Current in the Indian
Ocean. These are just a sampling of the seventeen major surface currents found in the world’s
oceans.

CAUSES:
Ocean currents are influenced by a variety of different forces that act to propel the water both on
the surface and in deep ocean waters. This movement has a significant effect on the earth's
weather.

Surface current:
Currents found in the upper 1,300 feet of the ocean are called surface currents. Let's examine
some of the forces that determine the direction of these currents.

1. Gravity
The surface of the ocean is not even. Due to this, gravity has an impact on the flow of water in
the ocean. The earth's gravity pulls at water, causing it to flow downward from higher surface
levels. You will notice the impact of gravity as it is mentioned alongside various other forces
throughout this lesson.
2. Wind
Wind is the driving force behind our oceans' surface currents. In other words, most surface
currents are caused by wind, which has the greatest impact on these currents. As the wind blows
over the water's surface, it produces friction. This friction pushes the water along and forms a
current moving in the same direction the wind is blowing. The current will continue in the
direction of the wind until other factors, such as nearing a land mass or colliding with another
ocean current, cause the water to build up and move in different ways.
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The general flow of ocean surface currents

and the gyres that are formed.

3. Coriolis effect
The spinning of the earth deflects movement. This is called the Coriolis effect. We usually see no
impact from the spinning of the earth, but we do notice its effect on surface currents because they
are large and move over long distances. The Coriolis effect comes into play when water being
pushed by the wind piles up into mounds. As gravity pulls the water down the slope of the
mound, the Coriolis effect forms a current that creates spiral patterns called gyres that help push
the current forward. These gyres move clockwise in the Northern Hemisphere and
counterclockwise in the Southern Hemisphere.
4. Continental deflection
We briefly mentioned earlier that nearing a land mass is one factor that causes water to build up
and change direction. When this occurs near a very large land mass, or continent, it is
called continental deflection. Since the earth is not completely covered in water, continental
deflection plays a large role in the overall direction of surface currents. The water can't travel
over or through the continent so it is forced to move around it.

5. The rise and fall of the tides.

Tides create a current in the oceans, which are strongest near the shore, and in bays and estuaries
along the coast. These are called "tidal currents." Tidal currents change in a very regular pattern
and can be predicted for future dates. In some locations, strong tidal currents can travel at
seppeds of eight knots or more.

Deep water current:

Deep water currents, also called thermohaline circulation, are found below 400 meters and make
up about 90% of the ocean. Like surface currents, gravity plays a role in the creation of deep
water currents but these are mainly caused by density differences in the water.
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1.Thermohaline circulation

This is a process driven by density differences in water due to temperature (thermo) and salinity
(haline) variations in different parts of the ocean. Currents driven by thermohaline circulation
occur at both deep and shallow ocean levels and move much slower than tidal or surface
currents.

Density differences are a function of temperature and salinity. Warm water holds less salt than
cold water so it is less dense and rises toward the surface while cold, salt laden water sinks. As
the warm water rises though, the cold water is forced to rise through upwelling and fill the void
left by the warm. By contrast, when cold water rises, it too leaves a void and the rising warm
water is then forced, through downwelling, to descend and fill this empty space, creating
thermohaline circulation.

2. Global Conveyor Belt

Thermohaline circulation is known as the Global Conveyor Belt because its circulation of warm
and cold water acts as a submarine river and moves water throughout the ocean.

3. Topography

seafloor topography and the shape of the ocean’s basins impact both surface and deep water
currents as they restrict areas where water can move and "funnel" it into another.
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TYPES:
Oceanographers have developed a number of methods of classifying currents in order to
facilitate descriptions of their physics and geography. Currents may be referred to according to
their forcing mechanism as either wind driven or thermohaline.

Alternatively, they may be classified according to their depth (surface, intermediate, deep or
bottom). The surface circulation of the world’s oceans is mostly wind driven. Thermohaline
currents are driven by differences in heat and salt and are associated with the sinking of dense
water at high latitudes; the currents driven by thermohaline forces are typically subsurface.

This classification scheme is not unambiguous; the circumpolar current, which is wind driven,
extends from the surface to the bottom. A periodic current is one for which the speed or
direction changes cyclically at somewhat regular intervals, such as a tidal current. A seasonal
current is one which changes in speed or direction due to seasonal winds. The mean circulation
of the ocean consists of semi-permanent currents which experience relatively little periodic or
seasonal change. A coastal current flow roughly parallel to a coast, outside the surf zone, while a
longshore current is one parallel to a shore, inside the surf zone, generated by waves striking the
beach at an angle. Any current some distance from the shore may be called an offshore current,
and one close to the shore an inshore current. Rip currents are another type of coastal current
that form where underwater land formations prevent waves from flowing straight back out to sea.
They result from spent waves (or waves that have already crashed) funneling out of a narrow
opening, like a break in a sandbar, with great force.

Yet another type of coastal current called upwelling occurs when winds displace surface water
by blowing it away and deeper water rises up to replace it. The opposite process, downwelling,
occurs when wind blows surface water towards a barrier, like the coastline, and the resulting
accumulation of water forces the water on top to sink. Both of these processes can occur in the
open ocean as well.

Upwelling and downwelling are crucial to the cycling of nutrients in the ocean. The cold, deeper
layers of water are rich in nutrients and carbon dioxide, while the warmer surface waters are rich
in oxygen. When the layers trade places, the nutrients and gases do too.

Some important currents:

Antarctic circumpolar

The ocean body surrounding the Antarctic is currently the only continuous body of water where
there is a wide latitude band of open water. It interconnects
the Atlantic, Pacificand Indian oceans, and provide an uninterrupted stretch for the prevailing
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westerly winds to significantly increase wave amplitudes. It is generally accepted that these
prevailing winds are primarily responsible for the circumpolar current transport. This current is
now thought to vary with time, possibly in an oscillatory manner.

Deep ocean
In the Norwegian Sea evaporative cooling is predominant, and the sinking water mass, the North
Atlantic Deep Water (NADW), fills the basin and spills southwards through crevasses in
the submarine sills that connect Greenland, Iceland and Britain. It then flows along the western
boundary of the Atlantic with some part of the flow moving eastward along the equator and then
poleward into the ocean basins. The NADW is entrained into the Circumpolar Current, and can
be traced into the Indian and Pacific basins. Flow from the Arctic Ocean Basin into the Pacific,
however, is blocked by the narrow shallows of the Bering Strait.
Also see marine geology about that explores the geology of the ocean floor including plate
tectonics that create deep ocean trenches.
Western boundary
An idealised subtropical ocean basin forced by winds circling around a high pressure
(anticyclonic) systems such as the Azores-Bermuda high develops a gyre circulation with slow
steady flows towards the equator in the interior. As discussed by Henry Stommel, these flows are
balanced in the region of the western boundary, where a thin fast polewards flow called
a western boundary current develops. Flow in the real ocean is more complex, but the Gulf
stream, Agulhas and Kuroshio are examples of such currents. They are narrow (approximately
100 km across) and fast (approximately 1.5 m/s).
Equatorwards western boundary currents occur in tropical and polar locations, e.g. the East
Greenland and Labrador currents, in the Atlantic and the Oyashio. They are forced by winds
circulation around low pressure (cyclonic).
Gulf stream
The Gulf Stream, together with its northern extension, North Atlantic Current, is a powerful,
warm, and swift Atlantic ocean current that originates in the Gulf of Mexico, exits through the
Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland to the
northeast before crossing the Atlantic Ocean.
Kuroshio currents
The Kuroshio Current is an ocean current found in the western Pacific Ocean off the east coast
of Taiwan and flowing northeastward past Japan, where it merges with the easterly drift of
the North Pacific Current. It is analogous to the Gulf Stream in the Atlantic Ocean, transporting
warm, tropical water northward towards the polar region.
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The Importance of Ocean Currents

Because ocean currents circulate water worldwide, they have a significant impact on the
movement of energy and moisture between the oceans and the atmosphere. As a result, they are
important to the world’s weather. The Gulf Stream for example is a warm current that originates
in the Gulf of Mexico and moves north toward Europe. Since it is full of warm water, the sea
surface temperatures are warm, which keeps places like Europe warmer than other areas at
similar latitudes.

The Humboldt Current is another example of a current that affects weather. When this cold
current is normally present off the coast of Chile and Peru, it creates extremely productive waters
and keeps the coast cool and northern Chile arid. However, when it becomes disrupted, Chile’s
climate is altered and it is believed that El Niño plays a role in its disturbance.
Like the movement of energy and moisture, debris can also get trapped and moved around the
world via currents. This can be man-made which is significant to the formation of trash
islands or natural such as icebergs. The Labrador Current, which flows south out of the Arctic
Ocean along the coasts of Newfoundland and Nova Scotia, is famous for moving icebergs into
shipping lanes in the North Atlantic.
Currents plan an important role in navigation as well. In addition to being able to avoid trash and
icebergs, knowledge of currents is essential to the reduction of shipping costs and fuel
consumption. Today, shipping companies and even sailing races often use currents to reduce
time spent at sea.

Finally, ocean currents are important to the distribution of the world’s sea life. Many species rely
on currents to move them from one location to another whether it is for breeding or just simple
movement over large areas.

Ocean Currents as Alternative Energy

Today, ocean currents are also gaining significance as a possible form of alternative energy.
Because water is dense, it carries an enormous amount of energy that could possibly be captured
and converted into a usable form through the use of water turbines. Currently this is an
experimental technology being tested by the United States, Japan, China, and some European
Union countries.

Whether ocean currents are used as alternative energy, to reduce shipping costs, or in their
natural to state to move species and weather worldwide, they are significant to geographers,
meteorologists, and other scientists because they have a tremendous impact on the globe and
earth-atmosphere relations.
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Atlantic Ocean Currents

The trade winds set up a system of equatorial currents which at times extends over as much as
50° of latitude or more. There are two westerly flowing currents conforming generally with the
areas of trade winds, separated by a weaker, easterly flowing countercurrent.

The North Equatorial Current originates to the northward of the Cape Verde Islands and flows
almost due west at an average speed of about 0.7 knot

. The South Equatorial Current is more extensive. It starts off the west coast of Africa, south of
the Gulf of Guinea, and flows in a generally westerly direction at an average speed of about 0.6
knot. However, the speed gradually increases until it may reach a value of 2.5 knots, or more, off
the east coast of South America. As the current approaches Cabo de Sao Roque, the eastern
extremity of South America, it divides, the southern part curving toward the south along the
coast of Brazil, and the northern part being deflected northward by the continent of South
America.

Between the North and South Equatorial Currents, the weaker North Equatorial Countercurrent
sets toward the east in the general vicinity of the doldrums. This is fed by water from the two
westerly flowing equatorial currents, particularly the South Equatorial Current.
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The Gulf Stream follows generally along the east coast of North America, flowing around
Florida, northward and then northeastward toward Cape Hatteras, and then curving toward the
east and becoming broader and slower. After passing the Grand Banks, it turns more toward the
north and becomes a broad drift current flowing across the North Atlantic. The part in the Straits
of Florida is sometimes called the Florida Current.

As the Gulf Stream continues eastward and northeastward beyond the Grand Banks, it gradually
widens and decreases speed until it becomes a vast, slowmoving current known as the North
Atlantic Current, in the general vicinity of the prevailing westerlies. In the eastern part of the
Atlantic it divides into the Northeast Drift Current and the Southeast Drift Current.

The Northeast Drift Current continues in a generally northeasterly direction toward the
Norwegian Sea. As it does so, it continues to widen and decrease speed. South of Iceland it
branches to form the Irminger Current and the Norway Current.

The Southeast Drift Current curves toward the east, southeast, and then south as it is deflected by
the coast of Europe. It flows past the Bay of Biscay, toward southeastern Europe and the Canary
Islands, where it continues as the Canary Current. In the vicinity of the Cape Verde Islands, this
current divides, part of it curving toward the west to help form the North Equatorial Current, and
part of it curving toward the east to follow the coast of Africa into the Gulf of Guinea, where it is
known as the Guinea Current. This current is augmented by the North Equatorial Countercurrent.

Pacific Ocean currents

Pacific Ocean currents follow the general pattern of those in the Atlantic. The North Equatorial
Current flows westward in the general area of the northeast trades, and the South Equatorial
Current follows a similar path in the region of the southeast trades. Between these two, the
weaker North Equatorial Countercurrent sets toward the east, just north of the equator.

After passing the Mariana Islands, the major part of the North Equatorial Current curves
somewhat toward the northwest, past the Philippines and Taiwan. Here it is deflected further
toward the north, where it becomes known as the Kuroshio, and then toward the northeast past
the Nansei Shoto and Japan, and on in a more easterly direction. Part of the Kuroshio, called the
Tsushima Current, flows through Tsushima Strait, between Japan and Korea, and the Sea of
Japan, following generally the northwest coast of Japan.
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The Kuroshio (Japanese for “Black Stream”) is so named because of the dark color of its water.
It is sometimes called the Japan Current. In many respects it is similar to the Gulf Stream of the
Atlantic. Like that current, it carries large quantities of warm tropical water to higher latitudes,

and then curves toward the east as a major part of the general clockwise circulation in the
Northern Hemisphere. As it does so, it widens and slows, continuing on between the Aleutians
and the Hawaiian Islands, where it becomes known as the North Pacific Current.

As this current approaches the North American continent, most of it is deflected toward the right
to form a clockwise circulation between the west coast of North America and the Hawaiian
Islands called the California Current. This part of the current has become so broad that the
circulation is generally weak. Near the coast, the southeastward flow intensifies and average
speeds are about 0.8 knot.

The South Equatorial Current, extending in width between about 4°N latitude and 10°S, flows
westward from South America to the western Pacific. After this current crosses the 180th
meridian, the major part curves in a counterclockwise direction, entering the Coral Sea, and then
curving more sharply toward the south along the east coast of Australia, where it is known as the
East Australian Current. The East Australian Current is the weakest of the subtropical western
boundary currents and separates from the Australian coast near 34°S. The path of the current
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from Australia to New Zealand is known as the Tasman Front, which marks the boundary
between the warm water of the Coral Sea and the colder water of the Tasman Sea. The
continuation of the East Australian Current east of New Zealand is the East Auckland Current.
The East Auckland Current varies seasonally: in winter, it separates from the shelf and flows
eastward, merging with the West Wind Drift, while in winter it follows the New Zealand shelf
southward as the East Cape Current until it reaches Chatham Rise where it turns eastward, thence
merging with the West Wind Drift

Near the southern extremity of South America, most of this current flows eastward into the
Atlantic, but part of it curves toward the left and flows generally northward along the west coast
of South America as the Peru Current or Humboldt Current.

Indian Ocean Currents

Indian Ocean currents follow generally the pattern of the Atlantic and Pacific but with
differences caused principally by the monsoons, the more limited extent of water in the Northern
Hemisphere, and by limited communication with the Pacific Ocean along the eastern boundary.

During the northern hemisphere winter, the North Equatorial Current and South Equatorial
Current flow toward the west, with the weaker, eastward Equatorial Countercurrent flowing
between them, as in the Atlantic and Pacific (but somewhat south of the equator). But during the
northern hemisphere summer, both the North Equatorial Current and the Equatorial
Countercurrent are replaced by the Southwest Monsoon Current, which flows eastward and
southeastward across the Arabian Sea and the Bay of Bengal.

Near Sumatra, this current curves in a clockwise direction and flows westward, augmenting the
South Equatorial Current, and setting up a clockwise circulation in the northern part of the Indian
Ocean. Off the coast of Somalia, the Somali Current reverses direction during the northern
hemisphere summer with northward currents reaching speeds of 5 knots or more. Twice a year,
around May and November, westerly winds along the equator result in an eastward Equatorial
Jet which feeds warm water towards Sumatra.
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As the South Equatorial Current approaches the coast of Africa, it curves toward the southwest,
through the Mozambique Channel between Madagascar and the mainland, and part flowing
along the east coast of Madagascar. At the southern end of this island the two join to form the
strong Agulhas Current, which is analogous to the Gulf Stream. This current, when opposed by
strong winds from Southern Ocean storms, creates dangerously large seas.

South of South Africa, the Agulhas Current retroflects, and most of the flow curves sharply
southward and then eastward to join the West Wind Drift; this junction is often marked by a
broken and confused sea, made much worse by westerly storms. A small part of the Agulhas
Current rounds the southern end of Africa and helps form the Benguela Current; occasionally,
strong eddies are formed in the retroflection region and these too move into the Southeastern
Atlantic.

The eastern boundary currents in the Indian Ocean are quite different from those found in the
Atlantic and Pacific. The seasonally reversing South Java Current has strongest westward flow
during August when monsoon winds are easterly and the Equatorial jet is inactive. Along the
coast of Australia, a vigorous poleward flow, the Leeuwin Current, runs against the prevailing
winds.
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OCEAN TIDE
PREFACE:
Tides are one of the most reliable phenomena in the world. As the sun rises in the east and the
stars come out at night, we are confident that the ocean waters will regularly rise and fall along
our shores. The following pages describe the tremendous forces that cause the world’s tides, and
why it is important for us to understand how they work.

Basically, tides are very long-period waves that move through the oceans in response to the
forces exerted by the moon and sun. Tides originate in the oceans and progress toward the
coastlines where they appear as the regular rise and fall of the sea surface. When the highest part
or crest of the wave reaches a particular location, high tide occurs; low tide corresponds to the
lowest part of the wave, or its trough. The difference in height between the high tide and the low
tide is called the tidal range.

A horizontal movement of water often accompanies the rising and falling of the tide. This is
called the tidal current. The incoming tide along the coast and into the bays and estuaries is
called a flood current; the outgoing tide is called an ebb current. The strongest flood and ebb
currents usually occur before or near the time of the high and low tides. The weakest currents
occur between the flood and ebb currents and are called slack tides. In the open ocean tidal
currents are relatively weak. Near estuary entrances, narrow straits and inlets, the speed of tidal
currents can reach up to several kilometers per hour.

CAUSES:
Tides are really all about gravity, and when we’re talking about the daily tides, it’s the moon’s
gravity that’s causing them.

As Earth rotates, the moon’s gravity pulls on different parts of our planet. Even though the moon
only has about 1/100th the mass of Earth, since it’s so close to us, it has enough gravity to move
things around. The moon’s gravity even pulls on the land, but not enough for anyone to really
tell.

When the moon’s gravity pulls on the water in the oceans, however, someone’s bound to notice.
Water, being a liquid and all, has a much easier time moving around. It bulges toward the moon,
and that bulge follows the moon as Earth turns beneath it.
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Water bulges toward the moon because of gravitational pull.

The ocean also bulges out on the side of Earth opposite the moon. If the moon's gravity is pulling
the oceans toward it, how can the ocean also bulge on the side of Earth away from the moon? It
does seem a little weird.

Gravity is the major force causing tides, but inertia is playing a part too. Inertia is matter’s
resistance to change. It wants to keep doing whatever it’s doing, whether that’s moving in a
straight line or staying still, until another force acts on it.

While the water closest to the moon is getting pulled, the water farthest from the moon is staying
right where it is. Both sides are experiencing gravity and inertia, but one always overpowers the
other.

On the side by the moon, gravity wins. On the side away from the moon, inertia wins.

These two bulges explain why in one day, there are two high tides and two low tides.

If Earth were perfectly round and completely covered in water, then high and low tides would be
equally proportioned everywhere. But Earth is not a perfect sphere, and there are big continents
getting in the way of water flowing and bulging in the direction of the moon. That’s why in some
places, the difference between high and low tide isn’t very big, and in other places, the difference
is drastic.

The sun has a part to play in tides as well. For instance, when the sun’s gravitational pull lines up
with the moon’s gravitational pull, the tides are more extreme.
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Gravitational pull of the sun and moon are combined

TYPES OF TIDE:
Diurnal tide cycle

An area has a diurnal tidal cycle if it experiences one high and one low tide every lunar day.
Many areas in the Gulf of Mexico experience these types of tides.

Semidiurnal tide cycle

An area has a semidiurnal tidal cycle if it experiences two high and two low tides of
approximately equal size every lunar day. Many areas on the eastern coast of North America
experience these tidal cycles.
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Mixed Semidiurnal tide cycle

An area has a mixed semidiurnal tidal cycle if it experiences two high and two low tides of
different size every lunar day. Many areas on the western coast of North America experience
these tidal cycles.

Spring Tides

The amplitude and frequency of such tides is affected by the moon's location as it revolves
around the Earth. The gravitational pull of the moon creates a tidal "bulge" at the location
directly beneath its location. Every two weeks or so, the moon aligns with the Earth and sun in a
straight line -- the new and full moon phases -- resulting in the maximum gravitational force on
our planet's oceans. These periods are referred to as "spring tides." During such times, high tides
are at their highest and low tides are at their lowest points of the two-week cycle.

Neap Tides

During the moon's first and third quarters, the sun's gravitational pull is at a right angle to the
moon's gravitational force. The result is a neap tide, which occurs about once a fortnight. Neap
tide is the period during which water levels are at their minimum tidal range: high tides are at
their lowest levels and low tides are at their highest levels. The moon's elliptical orbit also results
in varying tidal levels. When the moon is closest to Earth, tidal forces are strongest; when the
moon reaches its monthly apogees, tidal forces are at their weakest.

Other Tides

As high tide is building, the incoming flow of water is referred to as a flood tide or flood current.
When the tide flows out, the phenomenon is called an ebb tide or current. Slack tide occurs
between two such periods, when little or no tidal current exists. When tidal currents collide with
each other or with other currents such as those from rivers, estuaries or partially enclosed bays,
their flows can become aberrant. A strong tidal current that conflicts with other flows can cause a
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riptide below the water's surface. Riptides are often visible as a patch of dark, calm water among
incoming surf. A violent tidal disturbance on the water's surface is referred to as a tide rip. Tide
rips are characterized by choppy water that may look like whitewater rapids surrounded by
otherwise calm or even glassy seas.

EFFECTS:
Tides and currents affect and influence the natural world and human society. Tides and
currents carry nutrients, moderate temperatures, and influence conditions in numerous
ecosystems.The relationship between society and tides and currents is obvious as coastal
cities built to withstand prescribed levels of tidal surge are now being impacted by record
breaking tidal surges, and the building of solid coastal structures do not allow waves to
dissipate energy on land but deflect their energy to other coastal areas along the shore.

Climate Change

There is no doubt that Earth's climate plays a vital role in determining which organisms thrive in
different areas across the world. As environmental conditions change, then organisms will be
affected. This is especially true for ecosystems along the land/ocean margin. As global
temperature and sea levels rise, the location, strength, and extent of tides, tidal surges, and
currents will be effected. As sea level rises, water will push across low-lying coastal areas and
modify existing shorelines. One example of how climate affects and has affected currents is
when thermohaline circulation was slowed or stalled during the last ice age.

As a large volume of fresh water accumulated in the North Atlantic, major ocean currents were
disrupted, diminishing the ocean's capacity to distribute heat around the entire planet. This
disruption impacted world climate, which influenced glaciers' extent on land. The glacier's
forming displaced the location of shorelines worldwide. Much of the coastal land area in the
Northern Hemisphere went from being under water to above water and exposed the previously
underwater continental shelf to the air. Mud on the continental shelf, then exposed to the
atmosphere, was eroded by winds increasing the concentration of particulate mater in the
atmosphere. This disrupted the amount of sunlight reaching Earth's surface further impacting
climate.

Warm surface waters in the ocean also provide the energy source for tropical storms. As the
surface waters of the ocean have warmed, so too has the energy source for storms. This may also
impact the severity and frequency of future storm systems. Although more storms may provide
increased regional mixing of ocean water and, an increased supply of nutrients for marine
organisms, human populations and infrastructure will likely be more adversely impacted.
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Ecosystems

Ecosystems that span several tidal zones include anchored plants, and animals, and ephemeral
species that move with the daily tides or during some portion of their life cycle. Intertidal
ecosystems can be found in estuarine environments and shallow water coastal communities.
Organisms that live in intertidal zones must be able to live both above and below water
depending on the tide. Other organisms depend on currents for survival. Coral reefs are
dependent on ocean currents to deliver their food to them (zooplankton) and disperse their
larvae. Reefs located in shallow waters are most at risk from tidal emersions which can lead to
bleaching and death. Without tides and currents these ecosystems would not exist.So, tide has
great influence in:
 Estuaries,
 Intertidal Zones,
 Coral Reefs, etc

Society

Tides and currents affect society directly and indirectly. Settlements in new lands were often
established along the coast and in safe harbors created at the mouth of tidal rivers. These rivers
provided freshwater, and access to fish populations that supported the growing coastal
communities and their wealth. These ports also grew into transportation hubs that received
manufactured goods and returned local bounty in the form of timber, fur, and fish.
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Global Distribution of Tides

Global distribution of tide of diurnal, semidiurnal and mixed tide has given below in the figure:

IMPORTANCE:
Important for commerce and science for thousands of years

• Tidal heights are necessary for navigation.

• Tides affect mixing, stratification and, as a result biological activity.

• Tides produce strong currents, up to 5m/s in coastal waters.

• Tidal currents generate internal waves over various topographies.

• The Earth's crust “bends” under tidal forces.

• Tides influence the orbits of satellites.

• Tidal forces are important in solar and galactic dynamics.

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REFERENCE:
1. Reddy, M.P.M. & Affholder, M. (2002). Descriptive physical oceanography: State of
the Art. Taylor and Francis. p. 249. ISBN 90-5410-706-5. OCLC 223133263.
2. Hubbard, Richard (1893). Boater's Bowditch: The Small Craft American Practical
Navigator. McGraw-Hill Professional. p. 54. ISBN 0-07-136136-7. OCLC 44059064.
3. Coastal orientation and geometry affects the phase, direction, and amplitude
ofamphidromic systems, coastal Kelvin waves as well as resonant seiches in bays. In
estuaries seasonal river outflows influence tidal flow.
4. "Tidal lunar day". NOAA. Do not confuse with the astronomical lunar day on the Moon.
A lunar zenith is the Moon's highest point in the sky.
5. Mellor, George L. (1996). Introduction to physical oceanography. Springer.
p. 169.ISBN 1-56396-210-1.
6. Tide tables usually list mean lower low water (mllw, the 19 year average of mean lower
low waters), mean higher low water (mhlw), mean lower high water (mlhw), mean
higher high water (mhhw), as well as perigean tides. These are mean values in the sense
that they derive from mean data."Glossary of Coastal Terminology: H–M". Washington
Department of Ecology, State of Washington. Retrieved 5 April 2007.
7. "Types and causes of tidal cycles". U.S. National Oceanic and Atmospheric
Administration (NOAA) National Ocean Service (Education section).
8. Swerdlow, Noel M.; Neugebauer, Otto (1984). Mathematical astronomy in Copernicus's
De revolutionibus 1. Springer-Verlag. p. 76. ISBN 0-387-90939-7.
9. "neap²". Oxford English Dictionary (2nd ed.). Oxford University Press. 1989. Old
English (example given from AD 469: forđganges nip - without the power of advancing).
The Danish niptid is probably from the English. The English term neap-flood (from
which neap tide comes) seems to have been in common use by AD 725.
10. Plait, Phil (11 March 2011). "No, the "supermoon" didn't cause the Japanese
earthquake". Discover Magazine. Retrieved 16 May 2012.