Marine Biology Chapter 20 - Tides, Waves, and Currents

Tide

The daily rise and fall of the ocean seen along the shore, produced by tidal change

Undersea earthquakes can generate a large wave, or __________.

Tsunami

Currents that move swiftly down the continental slope are...?

Turbidity Currents

Swells

Waves that have longer periods and more rounded crests

Tidal Bore

A lone wave formed by the incoming tide at sloping mouth of a river

Whitecap

A mixture of air and water from narrow wave crests blown by the wind

Current

A large mass of continuously moving ocean water

According to the diagram below of the moon and Earth, what would be the approximate time difference between one high tide and the next high tide?

6 Hours

Longshore Current

A current that moves parallel to shore, produced by waves that break at an angle to the shore

What is the difference between a rogue wave and a tsunami?

A rogue wave is a huge, lone wave that has very high crests and low troughs. They are formed when two or more large waves from a storm unite, or when waves meet opposing currents. A tsunami, on the other hand, is generated by a sudden disturbance in Earth's crust, such as seismic activity, like an earthquake, landslide, or volcanic eruption.

Wave Train

A series of waves, one followed by the other, moving in the same direction; produced when a steady wind blows

Explain why a wave breaks on the shore. What is the importance of its wavelength to this process?

A wave breaks onshore when the water depth is about half the wave's wavelength. Its wavelength is important to this process because it determines the point at which the wave will break onshore.

Which statement is correct?

An undertow is caused by wave action

Wave

An up-and-down movement of the ocean surface (a form of energy that moves across the water)

Gyres

Circular ocean currents caused by a deflection of water by the continents

Global ocean currents move...?

Clockwise north of the equator and counterclockwise south of the equator

What causes global ocean (surface) currents?

Currents are large masses of continuously moving ocean water. The largest currents are called global ocean currents. They are caused by a factor known as the Coriolis Effect, which states that the spinning Earth causes the winds and surface waters to move in a clockwise direction in the north and counterclockwise direction in the south. The winds help drive the movement of the ocean surface waters.

Rip Current

Fast, narrow current of waves moving seaward, formed when a sandbar breaks

Turbidity Current

Fast, subsurface current found along seep continental slope

Tsunami

Giant waves generated by sudden seismic activity in Earth's curst

A large current that moves across the ocean surface is called a...?

Global Ocean Current

Describe how the life cycles of the grunion and the horseshoe crab are timed to the rhythm of the tides.

Grunion (Leuresthes tenuis): life begins at high tide. During summer and spring, thousands of these fish swim up onto sandy beaches (carried in by high tide). This is called a grunion run, and it occurs ta night during the new moon and full moon when the tide is highest. The females wiggle into the sand and lay thousands of eggs as the males deposit sperm around them. Afterward, they are swept back into the sea. The spawning is timed so exactly that it occurs only on the second, third, and fourth days that follow a new or full moon. After the grunion eggs are fertilized, they incubate for two weeks until the next new or full moon occurs. Horseshoe Crab (Limulus polyphemus): during late May and early June, vast numbers of horseshoe crabs come together in shallow bays, marshes, and inlets along the Atlantic and Gulf coasts, waiting to come up on the beaches to spawn. The signal to begin is provided by the moon. During the new and full moons, when tide is highest, the crabs come ashore. The female produces a cluster of tiny eggs on her abdomen, and the eggs are fertilized by the male's sperm, and then deposited out in the sand by the female. The next two weeks, the eggs incubate until they hatch during the next full or new moon. When the high water reaches the eggs, they hatch and go out into the ocean.

All of the following can cause a tsunami except...?

Hurricane Winds

A coast that has two high tides and low tides each day, with the first set of tides being stronger than the second, has...?

Mixed Tides

The highest tides can occur during a...?

New Moon and Full Moon

Whirlpool

Rapid movement of surface waters in a circle; also called an "eddy"

A fast, narrow current that moves seaward is called a __________.

Rip Current

Large waves that form when waves meet opposing currents are...?

Rogue Waves

Sandbar

Sand eroded by wave action that gets deposited in a long hill offshore

Countercurrents

Slow, deep horizontal ocean currents that flow in opposite direction of surface currents

Coriolis Effect

States that the spin of Earth causes winds and surface waters to move clockwise in northern hemisphere and counterclockwise in the southern hemisphere

The whitecaps seen on waves at sea are caused by...?

Strong winds creating a mixture of air and water

Tidal Currents

Swift-moving currents parallel to shore, produced by tidal change

Rogue Waves

Tall, lone waves formed when waves meet other waves or currents

Spring Tides

The highest and lowest tides, produced twice each month by strong gravitational pull when sun, moon, and Earth are aligned

Turbidity

The measure of the level of clarity of murkiness of water

Why does the moon have a stronger influence on Earth's tides than the sun does?

The tides are caused because the moon pulls on Earth with a force called gravity. However, because the gravitational pull of the Moon is not strong enough to pull earth, it causes the ocean water facing the moon to be pulled towards it, producing a high tide. A low tide occurs on the side of the earth facing away from the tides. The sun also exerts a gravitational pull on Earth. Although the sun is much larger than the moon, its gravitational pull on earth is much less due to its distance from Earth.

Undertow

The returning current of water from a wave that breaks on the beach

Upwelling

The rising of a cold, nutrient-rich current from deep in the ocean

Which statement about the diagram is correct?

The ship's stern is in the trough of the wave

How do the moon and the sun cause Earth's tides?

The tides are caused because the moon pulls on Earth with a force called gravity. However, because the gravitational pull of the Moon is not strong enough to pull earth, it causes the ocean water facing the moon to be pulled towards it, producing a high tide. A low tide occurs on the side of the earth facing away from the tides. The sun also exerts a gravitational pull on Earth. Although the sun is much larger than the moon, its gravitational pull on earth is much less due to its distance from Earth.

Tidal Range

The vertical distance between low and high tide

Wave Height

The vertical distance between the top (crest) of a wave and the bottom (trough) of the preceding wave

A wave will break on the beach when...?

The water depth is less than half its wavelength

Vertical distance between low and high tides is the __________.

Tidal Range

Why are the spring tides the highest tides each month?

Twice each month, the moon, sun, and Earth are aligned, so the pulling forces are combined to produce the highest and lowest tides, called spring tides. This spring tide occurs during the new moon and full moon, which are exactly two weeks apart. They are the highest tides due to the amount of gravitational force exerted on the Earth.

As a result of wave action, in which direction will the boat move?

Up and down

The rising of nutrient-rich, deep waters is called an __________.

Upwelling

Convection currents in the ocean are characterized by...?

Warm water moving from the equator to the poles

What causes deep ocean currents (countercurrents)?

Warm water rises at the equator, flows until it cools, then sinks again at the poles. The cold-water currents (from the poles) that replace the rising currents at the equator flow below the surface. This causes deep ocean currents to be created.

How do temperature and salinity differences cause vertical ocean currents?

Water with high salinity is much denser, so it sinks below water with lower salinity. This causes a vertical ocean current to be created. In addition, the temperature differences can also produce vertical water currents. Cold water sinks because its molecules are closer together, making the water denser. Warm water rises because its molecules are in motion and are spaced farther apart, making it less dense.

A steady wind can produce a series of waves, or a __________.

Wave Train

Neap Tides

Weaker tides (not too high or low) that are produced twice each month

How do upwellings develop from vertical ocean currents?

When vertical currents rise to the surface from the depths, they often contain nutrient-rich sediments from the bottom. The rising of such waters from deep in the ocean is called an upwelling.

How are ocean swells different from whitecaps?

When waves extend beyond the windy area in which they are generated, they have longer periods and more rounded crests; these are called swells. A whitecap is formed when the narrow crests of a wave are blown off by the winds, creating a mixture of air and water.

How are waves formed? What determines their size and speed?

Wind blowing across the surface of the ocean causes waves to form. When the wind blows, it pushes on the ocean surface, causing the water to lift. A gentle wind produces smaller waves, but strong winds produce much larger waves. Generally, the wind's speed, length of time it blows, and distance it blows affects the size and speed of waves.

Use the Pythagorean Theorem to calculate the height of the wave in the diagram, given that side BC is 12 meters and side AC is 5 meters. Show all work.

a^2 + b^2 = c^2 (12)^2 + (5)^2 = c^2 144 + 25 = c^2 169 = c^2 Side AB = 13 meters, meaning that the wave height is 13 meters