• While there is only one global ocean, the vast body of water that covers 71
• percent of the Earth is geographically divided into distinct named regions.
• The boundaries between these regions have evolved over time for a variety of
• historical, cultural, geographical, and scientific reasons.
• Historically, there are four named oceans: the Atlantic, Pacific, Indian, and
• However, most countries - including the United States - now recognize the
• Southern (Antarctic) as the fifth ocean.
• The Pacific, Atlantic, and Indian are known as the three major oceans.
The Atlantic Ocean covers an area of
approximately 41,105,000 square miles.
As the second largest ocean basin, the Atlantic
Ocean borders the east coast of the U.S., while the
Pacific, Earth's largest ocean basin, borders the
U.S. West Coast.
The Arctic Ocean is the smallest of the world's five ocean
With an area of about 5.4 million square miles, the Arctic
Ocean is about 1.5 times as big as the United States. It is
bordered by Greenland, Canada, Norway, Alaska, and
Russia. The average depth of the Arctic Ocean is 12,000 feet
and it is 17,850 feet at its deepest point.
The Arctic Ocean is almost completely covered with ice for
the majority of the year and its average temperature seldom
rises above freezing. However, this ocean is anything but
A warming climate can cause seawater to expand and
ice over land to melt, both of which can cause a rise in
Sea level can rise by two different mechanisms with
respect to climate change.
First, as the oceans warm due to an increasing global
temperature, seawater expands—taking up more space
in the ocean basin and causing a rise in water level.
The second mechanism is the melting of ice over land,
which then adds water to the ocean.
Why is the Ocean Blue?
Big Sur coastline looking north to Bixby Canyon Bridge in California.
The ocean is blue because water absorbs colors in the
red part of the light spectrum. Like a filter, this leaves
behind colors in the blue part of the light spectrum for
us to see.
The ocean may also take on green, red, or other hues as
light bounces off of floating sediments and particles in
Most of the ocean, however, is completely dark. Hardly
any light penetrates deeper than 656 feet, and no light
penetrates deeper than 3,280 feet.
Runoff and Pollution
Although the ocean covers two-thirds of the surface of the
Earth, it is surprisingly vulnerable to human influences
such as overfishing, pollution from run-off, and dumping
of waste from human activity.
This kind of pollution can have serious economic and
health impacts by killing marine life and damaging
habitats and ecosystems.
Toxins from pesticides, fertilizers, and other chemicals
used on farms contaminate nearby rivers that flow into the
ocean, which can cause extensive loss of marine life in bays
and estuaries leading to the creation of dead zones.
The dumping of industrial, nuclear and other waste into
oceans was legal until the early 1970's when it became
regulated; however, dumping still occurs illegally
Oil and other chemicals can get into sediments, impacting
large coastal areas, threatening human health, and
reducing the economic well-being of regions that depend
on a healthy coastal environment.
Our ocean and coastal areas provide us with a lot – from
food, places to boat and swim, and wildlife to enjoy…the list
goes on. So when these areas become polluted and
unhealthy, it isn’t just bad for the environment, it’s also bad
for us. At NOS, scientists, economists, and other experts
are busy monitoring, assessing, and working to clean up
contaminants in the environment.
A wide range of chemicals can contaminate our water,
land, or air, impacting the environment and our
health. Most contaminants enter the environment
from industrial and commercial facilities; oil and
chemical spills; non-point sources such as roads,
parking lots, and storm drains; and wastewater
treatment plants and sewage systems.
Many hazardous waste sites and industrial facilities
have been contaminated for decades and continue to
affect the environment.
Contaminants in the environment can look and smell
pretty nasty, but their impacts go beyond just
aesthetics. Some pollutants resist breakdown and
accumulate in the food chain. These pollutants can be
consumed or absorbed by fish and wildlife, which in
turn may be eaten by us.
Chemicals can also get into sediments, impacting large
coastal areas, threatening human health, and reducing
the economic well-being of regions that depend on a
healthy coastal environment.
Eighty percent of pollution to the marine environment
comes from the land. One of the biggest sources is called
nonpoint source pollution, which occurs as a result of
Nonpoint source pollution includes many small sources,
like septic tanks, cars, trucks, and boats, plus larger
sources, such as farms, ranches, and forest areas.
Millions of motor vehicle engines drop small amounts of oil
each day onto roads and parking lots. Much of this, too,
makes its way to the sea.
Some water pollution actually starts as air pollution, which
settles into waterways and oceans.
Dirt can be a pollutant. Top soil or silt from fields or
construction sites can run off into waterways, harming fish
and wildlife habitats.
Eel grass, a type of submerged aquatic vegetation, supports
the life cycle of many fish and shellfish. The health of
submerged aquatic vegetation is an important
environmental indicator of overall ocean and estuary health.
Seagrasses in bays and lagoons, for instance, are vital to the
success of small invertebrates and fish. These small creatures are
a food source for commercial and recreational fish.
Seagrasses also stabilize sediments, generate organic material
needed by small invertebrates, and add oxygen to the
Underwater vegetation in shallow coastal waters also supports a
wide diversity of marine creatures by providing spawning,
nursery, refuge, and foraging grounds for many species.
There Importance to the Ecosystem
Hidden beneath the ocean waters, coral reefs team
with life. Fish, corals, lobsters, clams, seahorses,
sponges, and sea turtles are only a few of the
thousands of creatures that rely on reefs for their
Reef-building corals are restricted in their geographic
distribution by factors such as the temperature and the
salinity (salt content) of the water. The water must also
be clear to permit high light penetration.
Thousands of creatures rely on coral reefs for their
survival. Hidden beneath the ocean waters, reefs are
also some of the oldest ecosystems on the planet,
reflecting thousands of years of history.
Coral reefs are also living museums and reflect
thousands of years of history.
Today, these important habitats are threatened by a
range of human activities.
Many of the world’s reefs have already been destroyed
or severely damaged by water pollution, overfishing
and destructive fishing practices, disease, global
climate change, and ship groundings. However, we can
still protect and preserve our remaining reefs by acting
Are you aware Healthy coral reefs are
valuable to you.
Coral ecosystems are a source of food for millions; protect
coastlines from storms and erosion; provide habitat,
spawning and nursery grounds for economically important
fish species; provide jobs and income to local economies
from fishing, recreation, and tourism; are a source of new
medicines, and are hotspots of marine biodiversity.
These values contribute approximately $29.8 billion to
world economies each year. Continued decline of reefs will
have alarming consequences for people worldwide.
The top threats to coral reefs— change, unsustainable
fishing and land-based pollution—are all due to human
Coral, a sessile animal, relies on its
relationship with plant-like algae to build
the largest structures of biological origin on
Corals are sessile, which means that they permanently
attach themselves to the ocean floor, essentially "taking
root" like most plants do. We certainly cannot recognize
them by their faces or other distinct body parts, as we
can most other animals.
The corals benefit, in turn, as the algae produce oxygen,
remove wastes, and supply the organic products of
photosynthesis that corals need to grow, thrive, and
build up the reef.
More than merely a clever collaboration that has
endured between some of the tiniest ocean animals and
plants for some 25 million years, this mutual exchange is
the reason why coral reefs are the largest structures of
biological origin on Earth, and rival old-growth forests in
the longevity of their ecological communities.