OceansMrs. Hutchcroft

6th Grade Science

Ocean Water

• Oceans are important because they provide homes to many organisms

• Oceans provide resources, such as food, salt, and transportation

• Oceans provide water for precipitation• Oceans provide oxygen (70% of Earth’s

oxygen!) produced by ocean organisms

Formation of Oceans

• More than three billion years ago, oceans formed from volcanic water vapor that collected in the atmosphere and then fell as torrential rains

Composition of Ocean Water

• Ocean water contains many dissolved substances, such as calcium, magnesium, and sodium that make it taste salty

• Two most abundant elements in the dissolved salts are sodium and chloride ions, which combine to form a salt called halite• Salinity: a measure of the amount of solids, or

salts, dissolved in seawater• Ocean water contains 35 grams dissolved

substances per kilogram of water• Erupting volcanoes add elements such as sulfur

and chlorine to ocean water

Composition of Ocean Water

Dissolved Gases

• Gases enter the ocean from the atmosphere• Oxygen enters the ocean from the

atmosphere and photosynthesis of ocean organisms

• Carbon dioxide enters from the atmosphere and from respiration of ocean organisms; forms carbonic acid, which controls ocean acidity

• Nitrogen provides nutrients for plants and is used in plant and animal tissues – most abundant dissolved gas

Water Temperature and Pressure

• Both vary with depth• Three layers:

• Warm surface layer: receives sun energy; warmest surface layer is near the equator

• Thermocline: begins at a depth of about 200 m; temperatures rapidly drop with increasing depth

• Deep-water layer – extremely cold

Water Layers

Water Temperature and Pressure• Pressure, or force per unity area,

increases about 1atmosphere for every 10 meter increase in depth• For example: at a depth of 20 m, a

scuba diver would experience a pressure of 3 atm (1 atm of air + 2 atm of water)

Ocean Currents and Climate

Ocean Currents and Climates

• Mass movement or flow of ocean water• River within the ocean• Two types

• Surface and Deep

Surface Currents:• Wind that moves only the upper few hundred meters of

water• Gulf Stream-100 km wide current of warm water flowing

east across the North Atlantic Ocean• Discovered in the 1500s by Ponce de Leon and his

pilot Anton de Alaminos• Flows from Florida northeastward toward North

Carolina where it curves toward the east and becomes slower and broader

Surface CurrentsControlled by three factors

• Global winds- Cause surface currents to flow in the direction the wind is blowing

• Coriolis Effect• Continental Deflections

Winds Driving CurrentsTrade Winds - Push equatorial currents westward

Westerly Winds - Push polar currents eastward

Winds Near India - Reverse directions between summer and winter producing monsoons

• Coriolis Effect • The apparent curving of moving objects due to

the Earth’s rotation• Northern Hemisphere = clockwise• Southern Hemisphere = counter clockwise• Western coasts currents – cold; prevent

excessive summer warming• Eastern coasts currents – warm ; keep northern

climates mild

• Continental Deflections• Shape of continents change the direction of

current flow

Deep/Density Currents• Stream like movement of ocean water far below

surface; forms when more dense sea water sinks beneath less dense water

• Density currents help regulate global rainfall patterns and temperatures

• North of Iceland, a density current flows along the ocean floor toward the Atlantic Ocean and spreads into the Pacific and Indian Oceans; warm Gulf Stream water replaces this cold current

• Decreasing the temperature of water increases density

• Increasing the salinity of water increases density

Upwelling• The movement of deep, cold, nutrient rich

water to the surface

• Nutrients promote growth of fish and plants

• Areas are important fishing grounds

• Affects climate of coastal areas

Question 1

• What is a surface current and what causes them?

Answer

• Surface currents move water horizontally – parallel to the Earth’s surface

• They are powered by wind

Question 2

• What is the Coriolis Effect?

Answer

• The Coriolis effect is the shifting of winds and surface currents caused by Earth’s rotation.

Question 3

• What is upwelling?

Answer

• Upwelling is a vertical circulation in the ocean that brings deep, cold water to the ocean surface.

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Waves

Rhythmic movement that carries energy through water and is 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

Still Water

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 unless the wave is breaking on shore.

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.

• Wave Erosion – wears away both rocky shores and beaches

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

Tides

• The rise and fall in sea level, caused by gravity from Earth, Moon, and Sun is called a tide.

• Caused by a giant wave.

• 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

What is the Tidal Range?

• HT = 30 ft, LT = 20 ft

• HT = 20 ft, LT = 12 ft

• HT = 50 ft, LT = 20 ft

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.

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Gravitational Effect of the Sun

• 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

Life in the Oceans

• Types of life are classified by WHERE organisms live in the ocean:• Plankton: tiny marine animals that float in the

upper ocean layers (e.g. eggs of ocean animals, very young fish, larvae jellyfish and crabs, and tiny adults of some organisms)

• Nekton: animals that swim rather than drift in the currents (e.g. fish, whales, shrimp, turtles, and squid)

• Bottom dwellers: can burrow in sediments, walk or swim on the bottom, or be attached to the seafloor (e.g. anemones, crabs, corals, sea cucumbers, sea star, sponges)

Ocean Ecosystems

• Community of organisms and nonliving factors such as sunlight, water, nutrients, sediment, and gases• Producers: organisms hat make their own food

through photosynthesis or chemosynthesis• Consumers: eat producers to get energy• Decomposers: break down materials and

release them back into the ecosystem• Energy is transferred from producers to

consumers and decomposers through food chains and webs

• Ocean nutrients are recycled through the ecosystem, particularly in coral reefs