Composition and motion
Oceans - Composition
Dissolved Gases
• Ocean water is a complex mixture of chemicals that
sustains a variety of plant and animal life.
• The two main gases in the atmosphere,
– nitrogen, N2, and
– oxygen, O2,
are also the main gases dissolved in ocean water.
• While carbon dioxide, CO2, is not a major
component of the atmosphere, a large amount of
this gas is dissolved in ocean water.
• Gases can enter the ocean from streams,
volcanoes, organisms, and the atmosphere.
Temperature and Dissolved
• Gases dissolve more readily in cold water
than in warm water.
• If the water temperature rises, gases will
be released into the atmosphere.
• Therefore, the ocean and the atmosphere
are continuously exchanging gases as
water temperature changes.
Dissolved Solids
• Ocean water is 96.5% pure water, or H2O.
• Dissolved solids make up about 3.5% of the mass of
ocean water.
• These dissolved solids, commonly called sea salts, give
the ocean its salty taste.
Most Abundant Elements
The six most abundant elements in ocean water are:
Dissolved Solids
• The salt halite, which is made of
sodium and chloride ions, makes
up more than 85% of the ocean’s
dissolved solids.
• Trace elements are elements that
exist in very small amounts.
Sources of Dissolved Solids
• Most of the elements that form sea salts
come from three main sources:
– volcanic eruptions,
– chemical weathering of rock on land, and
– chemical reactions between sea water and newly
formed sea-floor rocks.
• Each year, rivers carry about 400 billion
kilograms of dissolved solids into the ocean.
Sources of Dissolved Solids
• As water evaporates from the ocean, salts
and other minerals remain in the ocean.
Salinity of Ocean Water
• salinity a measure of the amount of dissolved
salts in a given amount of liquid
• Salinity is measured by the number of grams of
dissolved solids in 1,000 g of ocean water.
• The ocean is about 3.5% salts. (fresh water is
less than 0.1% salt or has a salinity of 1‰.)
(Modern instruments measure salinity by recording
the conductivity of water, or how easily electricity
moves through the water. The higher the salinity
of water, the better its conductivity.)
Factors that Change Salinity
• Where the rate of evaporation is high, the
salinity of surface water increases.
• Therefore, in equatorial water, where the rate of
precipitation is highest, the salinity is lower than
it is in subtropical water, where the rate of
evaporation is highest.
• Over most of the surface of the ocean, salinity
ranges from 33‰ to 36‰.
• Salinity at particular locations can vary greatly.
• September 2005
Temperature of Ocean Water
• Like ocean salinity, ocean temperature
varies depending on depth and location on
the surface of the oceans.
• The range of ocean temperatures is
affected by the amount of solar energy an
area receives and by the movement of
water in the ocean.
Surface Water
• The mixing of the ocean’s surface water
distributes heat downward to a depth of 100m to
• The temperature of surface water decreases as
latitude increases. Therefore, polar surface
waters are much cooler than the surface waters
in the tropics.
• Because ocean water freezes at about -1.9°C,
vast areas of sea ice exist in polar oceans.
• In the middle latitudes, the ocean surface
temperature varies depending on the seasons.
Density of Ocean Water
• density the ratio of the mass of a substance to
the volume of the substance;
• Two factors affect the density of ocean water:
salinity and the temperature of the water.
• The large amount of dissolved solids in ocean
water makes it denser than pure fresh water.
• Ocean water becomes denser as it becomes
colder and less dense as it becomes warmer.
Density of Ocean Water
• Water temperature affects the density of
ocean water more than salinity does.
• Therefore, the densest ocean water is
found in the polar regions, where the
ocean surface is the coldest.
– This cold, dense water sinks and moves
through the ocean basins near the ocean
World’s Ocean conveyor belt
Ocean Waves
• wave a periodic disturbance in a solid, liquid, or
gas as energy is transmitted through a medium
• One kind of wave is described as the periodic
up-and-down movement of water.
• A wave has two basic parts-a crest and a trough.
• The crest is the highest point of a wave.
• The trough is the lowest point between two
• The wavelength is the horizontal distance
between two consecutive crests or between two
consecutive troughs.
Draw a wave
Wave Energy
• The longer wind blows from a given direction,
the more energy is transferred from wind to
water and the larger the wave becomes.
• Because of their large surface area, larger
waves receive more energy from the wind than
smaller waves do.
• Thus, larger waves grow larger and smaller
waves die out.
(The energy is transferred from the wind to waves
by friction)
Why do waves break?
• As the wave moves in to shore, the bottom
gets shallower and shallower.
• If the bottom is shallower, the wave moves
slower. As the wave approaches the
shore, the leading edge of the wave is in
shallower water than the trailing edge.
Why do wave break?
The top of the wave tumbles forward, eventually
breaking over the leading edge.
• In this one limited situation, it is true that for a
short time the water is actually moving forward
with the wave; the water in the crest of the wave
is carried forward by its greater speed.
• The wave starts to break at the ‘depth of
disturbance, which is about half the wave
Ocean Currents
• current a horizontal movement of water in
a well-defined pattern, such as a river or
• Scientists place ocean currents into two
major categories:
– surface currents
– deep currents.
Surface current
• a horizontal movement of ocean water that is
caused by wind and that occurs at or near the
ocean’s surface
• Surface currents are controlled by three factors:
– air currents (wind)
– Earth’s rotation
– location of the continents
• Because wind is moving air, wind has kinetic
• As energy is transferred from the air to the
ocean, the water at the ocean’s surface begins
to move.
Factors That Affect Surface Currents:
Coriolis Effect
• Coriolis effect the apparent
curving of the path of a
moving object from an
otherwise straight path due to
Earth’s rotation
• Wind belts and ocean
currents follow a curved or
circular pattern that is caused
by Earth’s rotation.
Global Wind Belts
Global wind belts, such as
the trade winds and
westerlies, are a major
factor affecting the flow
of ocean surface water.
• In both hemispheres,
trade-wind belts push
currents westward
across the tropical
latitudes of all three
major oceans.
• Westerlies push ocean currents eastward in the higher latitudes
of the Northern and Southern Hemispheres.
Continental Barriers
• The continents act as
barriers to surface
• When a surface current
flows against a
continent, the current is
deflected and divided.
• The continents are
another major influence
on surface currents.
• gyre a huge circle of
moving ocean water
found above and below
the equator
• Wind belts and the
Coriolis effect cause
huge circles of moving
water, called gyres, to
• In the Northern Hemisphere, water flow in gyres is
to the right, or clockwise.
• In the Southern Hemisphere, the flow is to the left,
or counterclockwise.
Major Surface Currents
Major Surface Currents
Equatorial Currents
• Warm equatorial currents are located in
the Atlantic, Pacific, and Indian Oceans.
• Each of these oceans has two warm-water
equatorial currents that move in a
westward direction.
• Between these westward-flowing currents
lies a weaker, eastward-flowing current
called the Equatorial Countercurrent.
Major Surface Currents,
Currents in the Southern Hemisphere
• In the most southerly regions of the
oceans, constant westward winds produce
the world’s largest current, the Antarctic
Circumpolar Current, also known as West
Wind Drift.
• No continents interrupt the movement of
this current that completely circles
Antarctica and crosses all three major
Major Surface Currents,
Currents in the North Atlantic
• Gulf Stream the swift, deep, and warm Atlantic
current that flows along the eastern coast of the
United States toward the northeast
• South of Greenland, the Gulf Stream widens and
slows until it becomes a vast, slow-moving warm
current known as the North Atlantic Current.
• Near western Europe, the North Atlantic Current
Major Surface Currents,
Currents in the North Atlantic, continued
• The Gulf Stream, the North Atlantic
Current, the Canary Current, and the
North Equatorial Current form the North
Atlantic Gyre.
• At the center of this gyre lies a vast area of
calm, warm water called the Sargasso
Major Surface Currents,
Currents in the North Pacific
• The patterns of currents in the North Pacific is
similar to that in the North Atlantic.
• The warm Kuroshio Current, the Pacific
equivalent of the Gulf Stream, flows northward
along the east coast of Asia. This current then
flows toward North America as the North Pacific
• It eventually flows southward along the
California coast as the cool California Current.
Deep Currents
• deep current a streamlike movement of
ocean water far below the surface
• Deep currents form as cold, dense water
of the polar regions sinks and flows
beneath warmer ocean water.
• The movement of polar waters is a result
of differences in density.
• Temperature determines density. Salinity,
too, helps determines the density of water.
Deep Currents, continued
Antarctic Bottom Water
• The temperature of the water near
Antarctica is very cold, 2 °C. The water’s
salinity is high. These two factors make
the water off the coast of Antarctica the
densest and coldest ocean water in the
• This dense, cold water sinks to the ocean
bottom and forms a deep current called
the Antarctic Bottom Water.
Deep Currents, continued
Deep Currents, continued
North Atlantic Deep Water
• In the North Atlantic, south of Greenland,
the water is very cold and has a high
salinity. This cold, salty water forms a deep
current that moves southward under the
northward flowing Gulf Stream.
• The dense, highly saline water of the
Mediterranean Sea forms a deep current
as it flows through the strait of Gibraltar
and into the less dense Atlantic Ocean.
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