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Oceanography
8th Grade
What are Earth’s five main oceans?
Almost three-fourths of Earth is covered by ocean water.
On a map, the continents appear as huge islands
surrounded by a vast global ocean.
Earth’s global ocean is divided into five main oceans.
In decreasing order of size, they are the Pacific Ocean,
Atlantic Ocean, Indian Ocean, Southern Ocean, and
Arctic Ocean.
What are some characteristics of ocean
water?
The chemical characteristics of ocean water include
salinity, or the amount and type of dissolved salts.
Chemical characteristics also include the amount and
type of gases in the seawater.
The physical characteristics of ocean water include
temperature and density.
The overall salinity of seawater is about 3.5 percent.
The salinity of seawater has remained relatively
steady, but it varies from place to place depending
on the entry of freshwater streams, precipitation, and
rate of evaporation.
The ocean has three temperature layers by depth.
The top layer, or surface zone, is the warmest layer.
In the next layer, the thermocline, water temperature
drops with increased depth faster than it does in other
layers.
The deep zone is the deepest layer and the coldest.
By latitude, surface water is warmest near the equator
and coldest near the poles.
By season, surface water is warmest in summer and
coldest in winter.
Density is a measure of the mass of a substance
divided by its volume. The density of ocean water
depends on temperature and salinity.
How is the ocean floor studied?
To learn about the ocean floor, scientists use
technology such as sonar, drills, underwater
exploration vessels, and satellites.
Sonar, which stands for sound navigation and ranging,
uses sound waves to measure distances. Sonar data
can be used to make maps of the ocean floor.
Satellites can measure variations in the height of the
ocean’s surface. The ocean floor’s features can affect
the height of the water above them.
To explore the oceans, scientists use underwater vessels,
some of which have pilots and researchers. Other vessels
are remotely operated.
Using equipment on large ships, scientists can drill and
collect cores, or long tubes of rock and sediment, from
the sea floor.
What are the two main regions of the
ocean floor?
The two main regions of the ocean floor are the
continental margin and the deep-ocean basin.
The continental margin is the edge of the continent
that is covered by the ocean.
The continental margin is divided into the continental
shelf, the continental slope, and the continental rise.
The deep-ocean basin begins at the end of the
continental margin and extends under the deepest
parts of the ocean.
The deep-ocean basin includes narrow depressions
and flat, smooth plains.
What are the features of the ocean floor?
A long, undersea mountain chain that forms along the
floor of the ocean is called a mid-ocean ridge.
Mid-ocean ridges occur at the boundaries of Earth’s
tectonic plates, where plates move apart from each
other.
This motion creates a crack in the ocean floor called
a rift, allowing hot magma to move upward through
the rift and cool to form new rock.
The large, flat, almost level area of the deep- ocean
basin is called the abyssal plain. This area is covered
with layers of fine sediment.
A long, narrow depression in the deep-ocean basin is
called an ocean trench. It forms where one tectonic
plate subducts another plate.
Volcanoes and earthquakes are common in and along
subduction zones.
Submerged volcanic mountains on the ocean floor
are called seamounts.
They may form at tectonic plate boundaries and also
far from plate boundaries over places called hot
spots.
If a seamount grows above sea level, it becomes a
volcanic island.
What are some properties of a wave?
A wave is any disturbance that transfers energy
through matter or empty space.
An ocean wave is a disturbance that transfer
energy through ocean water.
A wave is made up of two main parts: a crest,
which is the highest point of the wave, and a
trough, the lowest point of the wave.
The distance between two adjacent wave crests
or troughs is a wavelength.
Wave amplitude is half the distance between the
crest and the trough.
Frequency is the number of waves produced in a
given amount of time.
Wave period is a measurement of how much time it
takes for a wave to pass a fixed point. It is the
inverse of frequency.
Wave speed is how fast a wave travels. To calculate
a wave’s speed, multiply its wavelength by its
frequency.
What causes ocean waves?
Ocean waves are a type of wave known as a
mechanical wave. Mechanical waves carry energy
through matter, such as water.
Most ocean waves form when energy in the
atmosphere is transferred to the ocean’s surface.
Wind blows across the water’s surface and transfers
energy to the water, and this energy is carried by the
wave.
Ocean waves can also be produced by underwater
earthquakes, underwater landslides, and underwater
volcanoes.
If a meteorite or an asteroid landed in the ocean, it
could displace enough water to cause large waves.
What happens when a wave moves
through the water?
Ocean waves are formed when wind transfers energy
to the water. As the energy moves through the water,
so do the waves.
The water itself does not travel with the energy. But
water at the surface undergoes circular movement.
Wave energy affects surface water to a depth of
about half a wavelength.
What happens when a wave reaches the
shore?
Ocean waves transfer energy to the shore; water at
the wave bottom slows, but water at the top travels at
the original speed.
Waves break as gravity pulls crests down.
What is a tsunami?
A tsunami is a series of waves that form when a large
volume of ocean water is suddenly moved up or down.
This movement can be caused by earthquakes,
volcanic eruptions, landslides, or the impact of a
meteorite or asteroid.
When a tsunami approaches land, the waves slow down
and get taller as they interact with the ocean floor.
What are ocean currents?
Ocean currents are stream-like paths of
water in the ocean. A surface current is an
ocean current near the surface caused by
wind.
What affects surface currents?
The Coriolis effect causes surface currents to
curve right or left.
Continental deflection causes currents to
change direction when flowing toward land.
Energy from surface winds can transfer to
water, causing surface currents.
How do deep currents form?
A deep current is a stream-like movement of
ocean water far below the surface. It forms
when surface water becomes denser than
water below, causing it to sink and become
a deep current.
What are convection currents and how do
they transfer energy?
A convection current is any movement of
matter resulting from density differences.
Convection currents transfer energy when
warm water is moved to colder regions.
What is upwelling?
Upwelling is the movement of deep, cold,
nutrient-rich water to the surface.
Upwelling brings nutrients from the deep
ocean to the surface.
What do ocean currents transport?
Surface and deep currents and upwelling
move ocean water through ocean basins.
Matter transported by currents includes
water and dissolved solids and gases. Energy
is transported from areas near the equator
toward Earth’s poles.