Ocean Motion

Chapter 16

Why are oceans important?

• Food

• Minerals

-diamonds off the coasts of South Africa and Namibia as

well as deposits of tin, titanium and gold along the shores of Africa, Asia and South America. Oil and gas as well.

• Transporation

• Weather

-ocean currents keep some places warm and others cool.

Hurricanes develop over tropical water

How did oceans first form?

During Earth’s youth (it’s first billion years), Earth was more volcanically active than it is today. When volcanoes erupt they spew not only lava and ash but also water vapor. Scientists believe that this water vapor began to be stored in the atmosphere and over millions of years cooled enough to form storm clouds that led to A LOT of rain. This rain collected in basins (low areas on Earth) and formed oceans.

What makes up oceans?

• Dissolved gases

-oxygen, carbon dioxide, nitrogen

How would oxygen enter the ocean?

1. directly from the atmosphere

2. photosynthesis

How would carbon dioxide enter the ocean?

1. directly from the atmosphere

2. from organisms during respiration

Nitrogen enters the ocean only from the atmosphere.

Why is the ocean salty?

• Ocean water contains many dissolved salts

• These salts (chloride, sodium, sulfate, magnesium, calcium, potassium) exist in the ocean as ions

What are ions?

Atoms that carry a charge

Where did these ions come from?

-rocks that dissolve by rivers and groundwater

-erupting volcanoes can add ions like sulfate and chloride

The most common ions found in oceans are sodium and chloride. These ions combine to form halite, table salt.

Salinity

The measure of the amount of salts dissolved in seawater (grams salt/ kg seawater)

Ocean water is about 3.5% salt (35 grams dissolved salt per kilogram of ocean water)

The composition of the oceans is in balance, the amount of dissolved salts have stayed the same for hundreds of millions of years. The oceans are not getting saltier.

Desalination Plants

One example of how water is desalinated today

https://www.youtube.com/embed/aysj7696b0A

Ocean Currents

Section 2

Currents • What are currents?

- “Rivers” of circulating water

• Causes - Wind

- Rotating Earth

- Density Changes

Surface Ocean Currents • Broad, slow drift- water moves horizontally, parallel to the Earth’s surface

• never cross equator

• Wind generated

• circular paths

•Move only the upper part of seawater

•Can carry seeds and plants between continents •Surface currents and winds are affected by the Coriolis effect

Coriolis Effect

• The Coriolis effect also cases fluids to curve to the left in the southern hemisphere, in a counterclockwise direction

The Coriolis Effect is the movement of wind and water to the right or left that is caused by Earth’s rotation.

It causes fluids such as air and water to curve to the right in the northern hemisphere, in a clockwise direction.

Coriolis Effect

• The shapes of continents and other land masses affect the flow and speed of currents.

• Currents form small or large loops and move at different speeds, depending on the land masses they contact.

The Gulf Stream

• The Gulf Stream is a warm-water current that affects coastal areas of the southwestern United States by transferring lots of thermal energy and moisture to the surrounding air.

The cold California Current affects coastal areas of the southwestern United States.

Warm and cold surface currents

• Cold Surface Currents

-currents on the west coasts of continents originate at the poles where the water is colder (example: California Current)

• Warm Surface Currents

-currents on the east coasts of continents originate near the equator where the water is warmer (example: Gulf Stream)

More about warm and cold surface currents

Warm surface currents bring warm water from the equatorial regions to other areas of Earth.

As the warm water flows away from the equator, heat is released into the atmosphere warming it.

This transfer of heat influences the climate.

Upwelling

• Upwelling is the vertical movement of water toward the ocean’s surface.

• Upwelling occurs when wind blows across the ocean’s surface (due to Coriolis effect) and pushes water away from an area. Deeper colder water then rises to replace it.

Upwelling often occurs along

coastlines.

Upwelling brings cold, nutrient-rich water from deep in the ocean to the ocean’s surface.

Creates fishing grounds

Density Currents

• Density Currents are a type of vertical current that carries water from the surface to deeper parts of the ocean.

Density Currents are caused by changes in density rather than wind.

Density currents circulate thermal energy, nutrients and gases.

What makes water become more dense?

1. Increases in salinity (the amount of dissolved salts in water)

2. Decrease in temperature

How do temperature changes affect the density of water?

Heating a substance causes molecules to speed up and spread slightly further apart, occupying a larger volume that results in

a decrease in density.

Cooling a substance causes molecules to slow down and get slightly closer together, occupying a smaller volume that results

in an increase in density.

Density Currents continued

The denser water sinks to the bottom and is replaced by warmer, less dense water. This creates the current.

Density currents circulate ocean water slowly, a few meters a month

Ocean Waves and Tides

Section 3

Waves

•A Wave is a rhythmic movement that carries energy through matter or space.

• In oceans, waves move through seawater

Waves

Caused by:

•Wind

•Earthquakes

•Gravitational force of the Moon and Sun.

Parts of a Wave

• Crest – highest point of a wave

• Trough – lowest point of a wave

• Wave Height – vertical distance between the crest and the trough

• Wavelength – horizontal distance between two crests or two troughs

Wavelength

Wave Height

Crest

Trough

Wave Parts

Wave Movement

•When a wave passes through the ocean, individual water molecules move up and down but they do not move forward or backward.

Wave Movement

•When a wave breaks against the shore, the crest outruns the trough and the crest collapses.

•Called a breaker.

• In this case, water does move forward and backward.

•After the wave breaks, gravity pulls the water back to sea

Waves Caused by Wind

• When wind blows across a body of water, friction causes the water to move along with the wind.

• Wave Height depends on –

– Wind speed

– Distance over which the wind blows

– Length of time the wind blows

When the wind stops blowing, waves stop forming, however, existing waves continue moving for long distances even if the wind stops

Tides

• The rise and fall in sea level is called a tide.

• Caused by a giant wave produced by the gravitational pull of the sun and moon

• High tide is the rise in sea level

• Low tide is the drop in sea level

• One low-tide/high-tide cycle takes about 12 hrs and 25 min.

• Tidal range is the difference in ocean level between high-tide and low-tide

Tidal bores

• Tidal bore- tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travels up a river or narrow bay against the direction of the river or bay's current.

• Most often found in places with large tidal ranges

Gravitational Effect of the Moon

•Two big bulges of water form on the Earth:

–one directly under the moon

–another on the exact opposite side

•As the Earth spins, the bulges follow the moon.

http://rds.yahoo.com/S=96062883/K=Tides/v=2/l=IVI/*-http:/static.howstuffworks.com/gif/tides.gif

Gravitational Effect of the Sun

•The sun can strengthen or weaken the moon’s effects

•Spring Tides

–Earth, Moon, and Sun are lined up

–High tides are higher and low tides are lower than normal

Gravitational Effect of the Sun

•Neap Tides

–Earth, Moon, and Sun form right angles

–High tides are lower and low tides are higher than normal