THE DYNAMIC OCEAN

Ocean Circulation

Ocean Water is constantly in motion, powered by many different forces:Winds, Density differences, etc.

Ocean Circulation

Winds generate surface currents which influence coastal climate.

Winds produce waves, which carry energy to distant shores where their impact erodes the land.

Surface Circulation

Ocean currents are masses of ocean water that flow from one place to another.

Currents can be surface level or deep below.

Surface Circulation

The creation of the currents can be simple or complex.

In all cases, however, the currents that are generated involve water masses in motion.

Surface Currents

Surface currents are movements of water that flow horizontally in the upper part of the ocean’s surface.

Surface Currents

Surface currents develop from friction between the ocean and the wind that blows across its surface.

Surface Currents

Some currents do not last long and only affect small areas.

These water movements are responses to local or seasonal influences.

Surface Currents

Other currents are more permanent and extend over large portions of the ocean.

These are related to the general circulation of the atmosphere.

Gyres

Huge circular-moving current systems within an ocean basin that dominate the surfaces of the ocean.

Gyres

There are five main ocean gyres:North PacificSouth PacificNorth AtlanticSouth AtlanticIndian Ocean

Gyres

Another factor that influences the movement of ocean waters is the Coriolis Effect.

Coriolis Effect

The Coriolis Effect is the deflection of currents away from their original course as a result of Earth’s rotation.

Coriolis Effect

Because of Earth’s rotation, currents are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Gyres

The two different deflections from the Coriolis Effect is why currents in the south rotate differently from that of the north.

Gyres

There are four main currents within each gyre.

The tracking of floating objects reveal that it takes about six years to go all the way around the loop.

Question

Why do gyres in the Northern Hemisphere flow in the opposite direction of gyres in the Southern Hemisphere?

Ocean Currents and Climate

When currents from low-latitude regions move into higher latitudes, they transfer heat from warmer to cooler areas on the Earth.

Ocean Currents and Climate

The Gulf Stream, a warm water current brings water from the equator up to the North Atlantic.

Ocean Currents and Climate

This warmer water allows Great Britain and northwestern Europe to be warmer than one would expect.

Ocean Currents and Climate

The effects of the warm water currents are felt most in mid latitudes in winter.

The influence of cold currents are felt most in the tropics during the summer months.

Ocean Currents and Climate

As cold water currents travel toward the equator, they help moderate the warm temperatures of adjacent land areas.

Ocean Currents and Climate

Ocean currents play a major role in maintaining Earth’s heat balance.

They transfer heat from the tropics to the cold polar regions.

Ocean Currents and Climate

Ocean water movement accounts for about a quarter of the heat transport.

Winds account for the remaining three quarters.

Upwelling

Winds can also cause vertical movements.

Upwelling is the rising of the cold water from deeper layers to replace warmer surface water.

Upwelling

Upwelling is a common wind-induced vertical movement.

Upwelling

One type of upwelling, called coastal upwelling, is most characteristic along the west coasts of continents, such as California, western South America, and West Africa.

Upwelling

Coastal upwelling occurs when winds blow toward the equator and parallel to the coast.

Upwelling

Coastal winds combined with the Coriolis Effect cause surface water to move away from the shore.

As the surface layer moves away from the coast, it is replaced with water from below.

Upwelling

The slow upward movement of water from depths of 50 to 300 meters brings water that is cooler than the original surface water.

Upwelling

Upwelling brings greater concentrations of dissolved nutrients, such as nitrates and phosphates, to the ocean surface.

Upwelling

The nutrients from upwelling promote the growth of microscopic plankton, which in turn support

extensive populations of fish.

Upwelling

What is upwelling?

Deep-Ocean Circulation

In contrast to horizontal movement of surface currents, deep-ocean circulation has a significant vertical component.

Deep-Ocean Currents

The vertical component of deep-ocean currents accounts for the through mixing of deep-water masses.

Density Currents

Density currents are vertical currents of ocean water that results from density differences of water.

Density Currents

An increase in seawater density can be caused by a decrease in temperature or an increase in salinity.

Density Currents

Density changes due to salinity variations are important in very high latitudes, where water temperature remains low and relatively constant.

Density Currents

Most water involved in deep-ocean density currents begins in high latitudes at the surface.

When this water becomes dense enough it sinks, where its temperature and salinity remain largely unchanged.

Density Currents

By knowing the temperature, salinity, and density of a water mass, scientists are able to map the slow circulation of the water mass through the ocean.

Density Currents

Near Antarctica, surface conditions create the highest density water in the world.

This cold, salty water sinks to the sea floor, where it moves throughout the ocean basins in slow currents.

Density Currents

After sinking from the ocean surface, deeps waters will not reappear at the surface for an average of 500 to 2000 years.

Density Currents

These currents can also result from increased salinity of ocean water due to evaporation.

Density Currents

One example of evaporation causing a density current is when Mediterranean waters, which have a salinity of 38 ‰, flow into the Atlantic, salinity of 35 ‰.

Conveyor Belt

A simplified model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean through the Indian and Pacific oceans and back again.

Conveyor Belt

In the conveyor belt model, warm water in the ocean’s upper layers flows toward the poles.

When water reaches the poles it cools and drops to the bottom of the ocean.

Conveyor Belt

The water returns to the equator, as cold, deep water that eventually upwells to complete the circuit.

Conveyor Belt

As the conveyor belt moves around the globe, it influences global climate by converting warm water to cold water and releasing heat to the atmosphere.

Currents

Describe what the

“Conveyor Belt” is.

Waves and Tides

Waves created by storms release energy when they crash along the shoreline.

Sometimes this energy can be harnessed and used to generate electricity.

Waves

Ocean waves are energy traveling along the boundary between ocean and atmosphere.

Waves can transfer energy from a storm far out at sea over distances of several thousand kilometers.

Waves

The power of waves is noticeable along the shore, the area between land and sea where waves are constantly rolling in and breaking.

Waves

Some waves can be low and gentle, others can be are powerful as they pound the shore.

Waves

When observing waves, remember that you are watching energy travel through a medium, in this case water.

Waves

Most ocean waves obtain their energy and motion from the wind.

Waves

When a breeze is less than 3 km/hr, only small waves appear.

At greater wind speeds, more stable waves gradually form and advance with the wind.

Wave Terms

Crest—The high point on a waveTrough—The low point on a waveWave Height—The vertical distance

between trough and crest

Wave Terms

Wave Length—The horizontal distance between two successive troughs/crests

Wave Period—The time it takes one full wave to pass a fixed position.

Wave Terms

Waves

The height, length, and period that are eventually achieved by a wave depend on three factors:(1) wind speed(2) length of time wind has blown(3) Fetch

Waves

Fetch—The distance that the wave has travelled in the open water.

Waves

As the quantity of energy transferred from the wind to the water increases, both the height and steepness of the wave increases.

Waves

If enough energy is transferred into the wave, a critical point is reached where waves grow so tall that they topple over, forming breakers called whitecaps.

Wave Motion

Waves can travel great distances across ocean basins.

Waves were once tracked that formed in Antarctica, went through the Pacific Ocean.

Wave Motion

After traveling through the Pacific Ocean for more than 10,000 km, the waves finally expended their energy a week later along the shoreline of the Aleutian Islands of Alaska.

Wave Motion

The water itself does not travel the entire distance, but the wave does.

As the wave travels, the water particles pass the energy by moving in a circle.

Wave Motion

Observations of a floating object reveals that it moves not only up and down but also slightly forward and backward with each successive wave.

Wave Motion

Circular orbital motion allows energy to move forward through the water while the individual water particles that transmit the wave move around in a circle.

Wave Motion

The energy transmitted to a wave also is transmitted downward, where the circular motion diminishes until the movement of water particles becomes negligible.

Breaking Waves

As long as a wave is in deep water, it is unaffected by water depth.

As a wave approaches shore the water becomes shallower and influences the wave behavior.

Breaking Waves

The wave begins to “feel bottom” at a water depth equal to half of its wavelength.

Such depths interfere with the water movement as the wave slows its advance at the bottom.

Breaking Waves

As the wave advances toward the shore, the faster moving trailing waves catches up and decreases the wavelength and speed of the wave.

Breaking Waves

As the speed and length of the wave decrease the waves grows higher.

A critical point is reached when the wave is too steep to support itself, and the wave front collapses.

Breaking Waves

The turbulent water created by breaking waves is called surf.

The turbulent sheet of water from collapsing breakers, called swash, moves up the beach, then recedes back after it expends its energy

Breaking Waves

Waves

Tides

Tides are daily changes in the elevation of the ocean surface.

Their rhythmic rise and fall along coastlines have been noted throughout history.

Tides

Although known for centuries, tides were not well explained until Sir Isaac Newton applied the law of universal gravitation to them.

Tides

Newton showed that any two bodies are attracted to each other, and because the oceans and atmosphere are fluids, free to move, both are changed by this force.

Tides

Ocean tides result from the gravitational attraction exerted upon the Earth by the moon and, to a lesser extent, by the sun.

Tide-Causing Force

The primary body that influences the tides is the moon, which makes one complete revolution around Earth every 29.5 days.

Tide-Causing Force

The sun also influences the tides, but much less so than the moon.

The sun’s tide-generating effect is only about 46 % that of the moon’s

Tide-Causing Force

The force that produces tides on Earth is gravity.

Gravity is the force that attracts the Earth and the moon to each other.

Tide-Causing Force

On the side of the Earth closest to the moon, the force of gravity is greater.

At this time, water is pulled in the direction of the moon and produces a tidal bulge.

Tide-Causing Force

On the far side of the Earth, farthest from the moon, water is pulled from the Earth causing an equal bulge on the other side of the Earth, opposite the moon.

Tide-Causing Force

Because the position of the moon changes only moderately in a single day, the tidal bulges remain in place and the Earth rotates through them.

Tide-Causing Force

As the Earth rotates, the bulges produce high tide, and the troughs produce low tide.

Most places on Earth experience 2 high tide times, and 2 low tide times.

Tidal Cycle

Although the sun is farther away from the Earth than the moon, the gravitational attraction does play a role in producing tides.

Tidal Cycle

The sun’s influence produces smaller tidal bulges on Earth.

The influence of the sun on tides is most noticeable near the times of the full moon, and new moon.

Tidal Cycle

During the new and full moon phases the sun, Earth, and moon are aligned, and their forces are added together.

The combined forces result in higher high tides and lower low tides.

Tidal Cycle

The tidal range is the difference in height between successive high and low tides.

Tidal Cycle

Spring Tides are tides that have the greatest tidal range due to the alignment of the Earth, moon, and sun.

They are experienced during new and full moons.

Tidal Cycle

During first and third quarter moons, the sun and moon act at right angles of each other.

The gravitational influence of the two bodies partially offset each other.

Tidal Cycle

Neap Tides are the low tides near first and third quarter moons.

Each month there are two spring tides and two neap tides, each one about one week apart.

Tidal Cycle

Tides

What is the difference between neap tides and spring tides?

How are each formed?

Shoreline Processes and Features

Beaches and shorelines are constantly undergoing changes as the force of waves and currents act on them.

Shoreline Processes and Features

A beach is the accumulation of sediment found along the shore of a lake or ocean.

They are composed of whatever sediment is locally available.

Shoreline Processes and Features

Beaches may be made of mineral particles from erosion of beach cliffs or coastal mountains.

This sediment may be relatively coarse in texture.

Shoreline Processes and Features

Some beaches have a significant biological component.

Southern Florida beaches are composed of shell fragments and remains of organisms.

Shoreline Processes and Features

The sediment that makes up beaches doesn’t stay in one place.

Waves are constantly moving the sediments.

Forces on Shoreline

Waves along the shoreline are constantly eroding, transporting, and depositing sediment.

Many types of shoreline features can result from this activity.

Wave Impact

During calm weather, wave action is minimal.

During storms waves are capable of causing much erosion.

Wave Impact

Each breaking wave may hurl thousands of tons of water against the land, sometimes causing the ground to tremble.

Wave Impact

Cracks and crevices are quickly opened in cliffs, coastal structures, etc.

Water is forced into every opening, causing air in the cracks to become highly compressed.

Wave Impact

As the wave subsides, the air expands rapidly.

The expanding air dislodges rock fragments and enlarges and extends preexisting fractures.

Abrasion

In addition to erosion caused by wave impact and pressure, erosion by abrasion is also important.

Abrasion

Abrasion is the sawing and grinding action of rock fragments in the water.

Smooth, rounded stones and pebbles along the shore are evidence of continual grinding.

Abrasion

Waves are very effective at breaking down rock material and supplying sand to beaches.

Wave Refraction

Wave refraction, the bending of waves, plays an important part of shoreline processes.

Wave Refraction

Wave refraction affects the distribution of energy along the shore.

It strongly influences where and to what degree erosion, sediment transport, and deposition takes place.

Wave Refraction

Waves seldom approach the shore at right angles.

Most waves move toward the shore at a slight angle.

Wave Refraction

When they reach the shallow waters, of the smoothly sloping bottom, the wave crests are bent or refracted, and tend to line up nearly parallel to the shore.

Wave Refraction

The waves bend because as the wave approaches the shore the shallower bottom slows down that part of the wave, while the other part of the wave continues at full speed.

Wave Refraction

The change in speed causes the wave crests to become nearly parallel to the shore regardless of their original orientation.

Wave Refraction

Because of refraction, wave energy is concentrated against the sides and ends of headlands that project into the water, whereas wave action is weakened in bays.

Wave Refraction

As the waves enter into bays they reach the shallower areas near the headlands, and wave energy is concentrated more there than in the adjacent bays.

Wave Refraction

The refraction leads to erosion of the headlands, and deposition of sediments and the formation of sandy beaches in the bays.

Longshore Transport

Although waves are refracted, most still reach the shore at a slight angle.

These angled waves produce currents with the surf zone.

Longshore Transport

The current flow parallel to the shore move large amounts of sediment along the shore.

This type of current is called longshore current.

Longshore Transport

Turbulence in the surf zone allows longshore currents to easily move the fine suspended sand and to roll larger sand and gravel particles along the bottom.

Longshore Transport

Longshore currents can change direction because the direction that waves approach the beach changes with the seasons.

Longshore Transport

Longshore currents generally flow southward along both the Atlantic and Pacific shores of the United States.

Forces on the Shoreline

What is wave refraction?

What causes longshore currents?

Erosional Features

An assortment of shoreline features can be seen along the worlds coasts.

Erosional Features

The shoreline features vary depending on the type of exposed rock, the intensity of the waves, the nature of coastal currents, and what the coast is doing (stable, sinking, or rising)

Erosional Features

Shoreline features that originate primarily from the work of erosion are called erosional features.

Erosional Features

Sediment that is transported along the shore and deposited in areas where energy is low produce depositional features.

Erosional Features

Many coastal landforms owe their origin to erosional processes.

Such erosional features are common along the rugged irregular New England coast and steep shorelines of Western US.

Wave-Cut Cliffs and Platforms

Wave-cut cliffs result from the cutting action of the surf against the base of coastal land.

Wave-Cut Cliffs and Platforms

As the erosion progresses on the wave-cut cliffs, rocks that overhang the notch at the base of the cliff crumble into the surf, and the cliff retreats.

Wave-Cut Cliffs and Platforms

A relatively flat bench like structure, called a wave-cut platform, is left behind by the receding cliff.

Wave-Cut Cliffs and Platforms

The platform broadens as the wave attacks continue.

Some debris produced by the waves remains along the water’s edge as sediment on the beach, as the rest is transported further out.

Sea Arches and Sea Stacks

Headlands that extend into the sea are vigorously attacked by the waves because of refraction.

The surf erodes the rock selectively and wears away the softer rock at the fastest rate.

Sea Arches and Sea Stacks

At first, sea caves may form.When two sea caves from opposite

sides of a headland meet, a sea arch results.

Sea Arches and Sea Stacks

Eventually, the arch falls in, leaving an isolated remnant, or sea stack, on the wave-cut platform.

Depositional Features

Beachshore of a body of water that is covered in sand, gravel, or other larger sediments.

Depositional Features

Sediment eroded from the beach is transported along the shore and deposited in areas where wave energy is low.

These processes produce a variety of depositional features.

Splits, Bars, and Tombolos

Where longshore currents are active, several features related to the movement of sediment along the shore may develop.

Splits, Bars, and Tombolos

A spit is an elongated ridge of sand that projects from the land into the mouth of an adjacent bay.

Spits, Bars, and Tombolos

Often the end of a spit hooks landward in response to the dominant direction of the longshore current.

Spits, Bars, and Tombolos

Baymouth bar is a sandbar that completely crosses a bay, sealing it off from the open ocean.

Spits, Bars, and Tombolos

Bars tend to form across bays where currents are weak.

This weak current allows a spit to extend to the other side and form a baymouth bar.

Spits, Bars, and Tombolos

A tombolo is a ridge of sand that connects an island to the mainland or to another island.

A tombolo forms in much the same way as a spit.

Barrier Islands

The Atlantic and Gulf Coastal Plains are relatively flat and slope gently seaward.

The shore in these areas are characterized by barrier islands.

Barrier Islands

Barrier Islands are narrow sandbars parallel to, but separate from, the coast at distances from 3 to 30 km offshore.

Barrier Islands

From Cape Cod, Massachusetts, to Padre Islands, Texas, nearly 300 barrier islands rim the coast.

Barrier Islands

Some barrier islands begun as spits, that were later cut off from the mainland by wave erosion or by the general rise in sea level following the last glacial period.

Barrier Islands

Other barrier islands were created when turbulent waters in the line of breakers heaped up sand that had been scoured from the ocean bottom.

Barrier Islands

Other barrier islands may be former sand-dune ridges that began along the shore during the last glacial period, when sea level was lower.

As the ice melted, sea level rose and flooded the area behind the islands.

Stabilizing the Shore

Shorelines change rapidly in response to natural forces.

Storms are capable of eroding beaches and cliffs at rates that far exceed long-term average erosion.

Stabilizing the Shore

The bursts of erosion from storms effect the natural evolution of the coast and have a profound impact on people who reside in coastal areas.

Stabilizing the Shore

Erosion along the coast causes significant property damage.

Huge sums of money are spent anually to prevent erosion.

Protective Structures

Groins, breakwaters, and seawalls are some structures built to protect a coast from erosion or to prevent the movement of sand along a beach.

Protective Structures

Groins, barrier built at a right angle to a beach, are sometimes constructed to maintain or widen beaches that are losing sand.

Protective Structures

A breakwater, protective structure built parallel to the shore, protects boats form the force of large breaking waves by creating a quiet water zone near the shore.

Protective Structures

A seawall, designed to shield the coast and defend property from the forces of breaking waves, reduces energy of waves moving across an open beach, by reflecting the waves seaward.

Protective Structures

Protective structures are often only temporary solutions.

The structures themselves interfere with natural processes of erosion and deposition.

Protective Structures

As structures are built, often new structures need to be built to counteract the new problems that arise.

Scientists feel using these structures are more harmful than good.

Beach Nourishment

Beach nourishment is the addition of large quantities of sand to the beach system.

Beach Nourishment

Beach nourishment is an attempt to stabilize the shore without building protective structures.

By building the beach seaward, both beach quality, and storm protection are improved.

Beach Nourishment

The same processes that removed the sand in the first place will eventually wash away the replacement sand as well.

Beach Nourishment

Beach nourishment can be very expensive, due to the massive amount of sand that needs to be transported.

Beach nourishment can have detrimental effects, as well.

Beach Nourishment

In Hawaii they replaced the natural coarse beach sand with softer muddier sand, which resulted in increased cloudiness, which killed the offshore coral reefs.

Review

How do sea arches form?

What is a barrier island?