Earth’s Oceans

Essential Standard 2.3

Explain the structures and processes

within the hydrosphere.

Learning Objective 2.3.1

Explain how water is an energy agent due

to the transfer of heat by ocean currents

and formation of sea and land breezes due

to high heat capacity of water.

I Can StatementsAt the end of this lesson, you should be

able to say, with confidence:

• I can explain how deep ocean currents form.

• I can explain how surface currents form.

• I can explain surface and deep ocean currents

interact to produce upwelling.

• I can explain how ocean currents help balance the

heat energy on Earth.

• I can explain how the high heat capacity of water

helps moderate coastal climates.

The Blue Planet71% of Earth is covered by oceans.

Most of the landmass

is in the northern

hemisphere.

All of the oceans are

actually one vast,

interconnected body

of water.

Northern Hemisphere

Southern Hemisphere

View from above the poles

Major OceansThere are three major oceans: the Pacific, the

Atlantic, and the Indian.

The smaller Arctic and Antarctic oceans are

located near the poles.

Polar OceansThe Arctic and Antarctic oceans are

covered by vast expanses of sea ice,

particularly during the winter.

Light AbsorptionMost light only penetrates about 100 m of seawater,

below that depth is total darkness.

Different wavelengths of light

are absorbed differently, with the

longer red light wavelengths

being absorbed first.

Below a certain depth, red

objects light giant shrimp,

appear black.

Why is the Ocean Blue? Because the ocean absorbs all the colors of light before

it absorbs blue light, the blue light gets scattered more,

making the ocean appear blue.

The sky is blue for the same reason.

PhytoplanktonWithin the region that light can penetrate, live

microscopic, photosynthetic algae called phytoplankton.

Phytoplankton are the base of the marine food web

and contribute between 50 to 80% of the oxygen in

Earth’s atmosphere.

ZooplanktonZooplankton are microscopic animals that drift in the

ocean and feed upon the phytoplankton.

Zooplankton are generally the second level in the

marine food web.

Green Ocean Water Photosynthetic phytoplankton, like terrestrial plants, use

chlorophyll pigments during photosynthesis. Chlorophyll

absorbs red and blue light but reflects green light. This

is why plants and phytoplankton appear green.

Ocean water rich in

photosynthetic

phytoplankton, like

the Gulf Stream,

appears green, rather

than blue.

Tropical Ocean Water Due to warmer temperatures, tropical ocean water has

very little phytoplankton and is also very shallow, so

most of the light is reflected. Because of this we see

clear, light blue water.

Coral Reefs The shallow, clear tropical water allows coral reef

systems to thrive due to high amount of light penetration.

Coral are tiny stationary

animals that live in

colonies and produce

calcium carbonate or

limestone skeletons.

Each individual coral animal

is called a polyp.

Coral Reefs Tiny, photosynthetic algae, called zooxanthellae,

live on top of the coral polyps.

Living on top of the

coral helps the

algae reach the

sunlight it needs to

perform

photosynthesis.

The coral benefits from the oxygen the algae

produces during photosynthesis.

Mutualism When two different species benefit from a

relationship it is called mutualism.

Biologically DiverseOvertime, the skeletons of the coral build up to form

a reef that provides habitat for a large variety of

marine life.

Coral reefs are the

most biologically

diverse ecosystems

in the ocean and

are homes to more

than 25% of all

marine life.

SalinityThe average salinity of the ocean is 35 parts

per thousand, ppt.

However, salinity can vary a lot depending

upon evaporation levels and fresh water input.

Three Categories of Salt WaterBriny water is found in brine

ponds and have a salinity

greater than 50 ppt.

Saline water with salinities

between 50 – 30 ppt can be

found in the oceans, seas,

and salt water lakes.

Brackish water with salinities

between 30 and 0.5 ppt can

be found in estuaries

(mouths of rivers).

Sources of Ocean SaltMost of the salt in the oceans come from the

weathering of rock on land and are carried through

runoff to the ocean.

But some of the

salts come from

the remains of

marine animals,

volcanoes, and

hydrothermal

vents.

Density of Ocean WaterFreshwater has an average density of 1.0 g/mL. But,

because salt ions add to the overall mass of the water it

is dissolved in, ocean water is more dense than

freshwater.

The higher the salinity, the

greater the density.

The colder the temperature,

the greater the density.

Due to the range of ocean

temperatures and salinity,

density can vary between 1.02

and 1.03 g/mL.

Egg in

SaltwaterEgg in

Freshwater

Ocean TemperaturesOcean surface temperatures range from – 2oC in

polar waters to 38oC in tropical waters.

Water temperatures,

however, decrease

significantly with depth.

Thus, deep ocean

water is always cold,

even in tropical oceans.

Deepwater MassesWhen seawater freezes near the poles, the salt is not

incorporated into the ice and collects under the ice.

As a result the

water under the

ice increases in

salinity.

The higher salinity increases the density of the water,

causing it to sink and form a deep water mass.

Density CurrentsAs more and more salty, cold, dense water is added

at the poles, the deep water mass is pushed towards

the equator in what is called a density current.

Surface CurrentsAt the ocean surface, the warmer waters are driven

by Earth’s global wind systems.

The global wind systems will be covered more in depth in the Atmosphere unit,

right now we are just going to focus on the direction of the winds.

Coriolis EffectBecause the Earth rotates on its axis, wind is

deflected to the right in the northern hemisphere

and towards the left in the southern hemisphere.

This deflection of

the wind is called

the Coriolis Effect.

Winds moving

towards the

equator travel

towards the west.

Coriolis EffectWinds traveling from the equator to the poles are

still deflected to the right in the northern hemisphere

and to the left in the southern hemisphere.

But now the winds are

traveling towards the

east, instead of the west.

Click on this link to

watch a short video on

the Coriolis Effect

Direction of Surface CurrentsRecall that surface currents are mostly determined by

the direction of the global wind systems.

Surface currents

traveling towards the

equator travel

westward.

Surface currents

traveling towards the

poles travel eastward.

GyresWhen ocean currents encounter a land mass, the

water is deflected towards the north or south.

As a result of both the

Coriolis Effect and

landmasses, ocean

currents travel in

circular systems called

gyres (Ji urz).

Gyres rotate clockwise in the northern hemisphere

and counter-clockwise in the southern hemisphere.

The Gulf StreamThe Gulf Stream is part of the North Atlantic gyre and

brings warm water up from the Equator; along the east

coast of the United States; by the southern shores of

Greenland; and over to the England.

The warm ocean

current keeps the

climate in those areas

warmer than it would be

just based on latitude.

The Canary CurrentThe Canary Current is also part of the North Atlantic

gyre, only in this case, it brings cold water down along

the western coast of Africa towards the equator.

In this case, the

cool ocean

currents keep the

climates cooler

than they would be

based on just

latitude.

Heat BalanceThe gyre system of surface ocean currents help

balance the heat on Earth, bringing warm water

and air towards the poles and cool water and air

towards the tropics.

Without the gyre

system ocean

currents, it would be

a lot colder near the

poles and a lot

hotter near the

equator.

UpwellingWinds blowing from the north, along the western coast

of continents, cause surface water to begin moving.

The Coriolis Effect

acts on the moving

water, deflecting it to

the right of its

direction of

movement.

As a result, the warm surface water is moved offshore.

UpwellingAs warm surface water is moved offshore, deeper, cooler

water rises to replace it, in a process called upwelling.

Because plant and

animal wastes drift

downward, the

deeper, cooler water

is full of nutrients.

Due to the high levels of nutrients, places that

experience upwelling generally have abundant fish life.

Sunlight EnergyAbout half or 50% of the sunlight energy that

reaches Earth is absorbed by the land and water on Earth’s surface.

Even though the water and the land receive the same amount of sunlight, they both absorb the heat at

different rates.

Different Rates

Heat CapacityThe reason has to do with what is called the heat

capacity of the material involved.

Heat capacity is the capacity a material has to gain or lose heat.

Materials with a high heat capacity can absorb

a lot of heat energy before it experiences an increase in temperature.

Materials with a low heat capacity will experience an

increase in temperature after very little heat

absorption.

High Heat Capacity of WaterWater has a very high heat capacity. So, water can absorb a lot of heat before the temperature of the

water actually increases.

Low Heat Capacity of SandSand has a very low heat capacity. So, the

temperature of the sand increases after just a little bit of heat absorption.

Heat CapacityOnce the heat source is removed, substances with low heat capacities will cool down faster than substances

with high heat capacities.

On the beach at night, the sand feels very cool, but the temperature of the water doesn’t change

much from what it was during the day.

Effect of Temperature on AirWarm land or warm water transfer heat to the air above. As the air is warmed, its molecules

begin moving faster and spread out, making the air less dense.

As the air becomes less

dense, it begins to rise.

Effect of Temperature on AirOne the other hand, cool sand or water tends to

cool the air above. As the air cools, the molecules slow down and become compacted,

making the air more dense.

As the air becomes more dense, it sinks.

Wind or BreezeAs hot air rises, it begins to cool. Once it is cool, it

begins to sink. The process repeats, creating a cycle of moving air.

This process is called convection and results in the creation of a gentle

wind or breeze.

Sea BreezeDuring the day, the hot air over the land rises and the

cooler air, over the sea, moves towards land to replace the hot air.

This movement of air creates a very gentle sea breeze.

Land BreezeDuring the night, the land cools down much faster

than the sea. So, the air over the sea is warmer and rises. The cooler air over the land then moves in to

replace the rising sea air.

This movement of air creates a very

gentle land breeze.

Moderate Coastal ClimatesDue the sea and land breezes that are a result of the high heat capacity of water, coastal climates tend to

be more moderate than inland climates.

The End