Have
1,100 times the heat capacity of the atmosphere (99.9% of the heat
capacity of the Earth's fluids)
Contain
90,000 times as much water as the atmosphere (97% of the free water on the
planet)
Receive
78% of global precipitation
Origins of Oceans
NationalGeographic
Today 71% of the Earth is covered
with water, 29% by the 7 continents. The percentage covered by water will
increase as the Earth continues to warm and polar ice caps melt.
The
great body of water embracing the continents of the Earth is also known
as the world ocean. Its major subdivisions are the Pacific, the
Atlantic, the Arctic, the Indian, and the Southern oceans.
More
than one-half of the world's population lives within 60 miles (100 km)
of the ocean.
The
NOAA polar-orbiting satellites (POES) have been collecting sea surface
temperature data for over 22 years. This animation is a compilation of that data
from January 1985 - January 2007. Of note are the changes in the Gulf Stream, El
Nino and La Nina cycles in the Pacific, and the seansonal changes in sea ice
cover.
In
ancient times, the term seven seas was used to describe all known large
bodies of water. These were: the Indian Ocean, the Red Sea, the Persian
Gulf, the Black Sea, the Sea of Azov, the Adriatic Sea, and the Caspian
Sea. Today, the term seven seas is used to refer to the Arctic,
Antarctic, North Pacific, South Pacific, North Atlantic, South Atlantic,
and Indian Oceans.
Layers
of the Ocean
U.S.
Weather Service Graphic
Epipelagic Zone
This
surface layer is also called the sunlight zone and
extends from the surface to 660 feet (200 m). It is in this zone that most
of the visible light exists. With the light comes heating from sun. This
heating is responsible for wide change in temperature that occurs in this
zone, both in the latitude and each season. The sea surface temperatures
range from as high as 97°F (36°C) in the Persian Gulf to 28°F (-2°C)
near the north pole.
The sea surface temperature also "follows the sun". From the
earth's perspective, the sun's position in the sky moves higher each day
from winter to summer and lower each day from summer to winter. This change
in the sun's position from winter to summer means that more energy is
reaching the ocean and therefore warms the water.Interaction with the wind
keeps this layer mixed and thus allows the heating from the sun to be
distributed vertically. At the base of this mixing layer is the beginning of
the thermocline. The thermocline is a region where water temperature
decreases rapidly with increasing depth and transition layer between the
mixed layer at the surface and deeper water.
The depth and strength of
the thermocline varies from season to season and year to year. It is
strongest in the tropics and decrease to non-existent in the poler winter
season.
Mesopelagic
Zone
Below the epipelagic zone is
the mesopelagic zone, extending from 660 feet (200 meters) to 3,300 feet
(1,000 meters). The mesopelagic zone is sometimes referred to as the twilight
zone or the midwater zone as sunlight this deep is very faint.
Temperature changes the greatest in this zone as this is the zone with
contains the thermocline.
Because of the lack of light, it is within this zone that bioluminescence
begins to appear on life. The eyes on the fishes are larger and generally
upward directed, most likely to see silhouettes of other animals (for food)
against the dim light.
Bathypelagic Zone
The depths from 3,300 - 13,100
feet (1,000-4,000 meters) comprise the bathypelagic zone. Due to its
constant darkness, this zone is also called the midnight zone.
The only light at this depth (and lower) comes from the bioluminescence of
the animals themselves.
The temperature in the bathypelagic zone, unlike that of the mesopelagic
zone, is constant. The temperature never fluctuates far from a chilling 39°F
(4°C). The pressure in the bathypelagic zone is extreme and at depths of
13,100 feet (4,000 meters), reaches over 5850 pounds per square inch! Yet,
sperm whales can dive down to this level in search of food.
Abyssopelagic Zone
The Abyssopelagic Zone (or
abyssal zone) extends from 13,100 feet (4,000 meters) to 19,700 feet (6,000
meters). It is the pitch-black bottom layer of the ocean. The name (abyss)
comes from a Greek word meaning "no bottom" because they thought
the ocean was bottomless. Three-quarters of the area of the deep-ocean floor
lies in this zone. The water temperature is constantly near freezing and
only a few creatures can be found at these crushing depths. The deepest a
fish have ever been found was in the Puerto Rico Trench at 27,460 feet (8372
meters).
Hadalpelagic Zone
The deepest zone of the ocean,
the hadalpelagic zone extends from 19,700 feet (6,000 meters) to the very
bottom at 35,797 feet (10,911 meters) in the Mariana Trench off the coast of
Japan. The temperature is constant at just above freezing. The weight of all
the water over head in the Mariana Trench is over 8 tons per square inch
(the weight of 48 Boeing 747 jets).
Even at the very bottom life exists. In 2005, tiny single-celled organisms,
called foraminifera, a type of plankton, were discovered in the Challenger
Deep trench southwest of Guam in the Pacific Ocean.
The ocean has four
types of motion:
surface currents
The ultimate
reason for the world's surface ocean currents is the sun. The
heating of the earth by the sun has produced semi-permanent
pressure centers near the surface. When wind blows over the
ocean around these pressure centers, surface waves are generated
by transferring some of the wind's energy, in the form of
momentum, from the air to the water. This constant push on the
surface of the ocean is the force that forms the surface
currents.
Around the world,
there are some similarities in the currents. For example, along
the west coasts of the continents, the currents flow toward the
equator in both hemispheres. These are called cold currents as
they bring cool water from the poler regions into the topical
regions. The cold current off the west coast of the United
States is called the California Current.
Likewise, the
opposite is true as well. Along the east coasts of the
continents, the currents flow from the equator toward the poles.
There are called warm current as they bring the warm tropical
water north. The Gulf Stream, off the southeast United States
coast, is one of the strongest currents known anywhere in the
world, with water speeds up to 3 mph (5 kph).
These currents
have a huge impact on the long-term weather a location
experiences. The overall climate of Norway and the Bristish Isle
is about 18°F (10°C) warmer in the winter than other cites
located at the same latitude due to the Gulf Stream.
deep circulation
While ocean
currents are a shallow level circulations, there is global
circulation which extends to the depths of the sea called the
Great Ocean Conveyor. Also called the thermohaline circulation,
it is driven by differences in the density of the sea water
which is controlled by temperature (thermal) and salinity (haline).
In the northern
Atlantic Ocean, as water flows north it cools considerably
increasing its density. As it cools to the freezing point, sea
ice forms with the "salts" extracted from the frozen
water making the water below more dense. The very salty water
sinks to the ocean floor.
It is not static,
but a slowly southward flowing current. The route of the deep
water flow is through the Atlantic Basin around South Africa and
into the Indian Ocean and on past Australia into the Pacific
Ocean Basin.
National
Weather Service Graphic
If the water is
sinking in the North Atlantic Ocean then it must rise somewhere
else. This upwelling is relatively widepsread. However, water
samples taken around the world indicate that most of the
upwelling takes place in the North Pacific Ocean.
It is estimated
that once the water sinks in the North Atlantic Ocean that it
takes 1,000-1,200 years before that deep, salty bottom water
rises to the upper levels of the ocean.
tides
The change in the
water level with the daily tides from location to location
results from a many factors. The oceans and shorelines have
complex shapes and the depth, and configuration, of the sea
floor varies considerably.
As a result, some
locations only experience one high and low tide each day, called
a diurnal tide. Other locations experience two high and low
tides daily, called a semi-diurnal tide. Still, other sites have
mixed tides, where the difference in successive high-water and
low-water marks differ appreciably.
Another factor in
the variation of tides is based on the orbit of the moon around
the earth and the earth around the sun. Both orbits are not
circles but ellipses. The distance between the earth and moon
can vary by up to 13,000 miles (31,000 km). Since the tidal
force increase with decreasing distance then tides will be
higher than normal when the moon is at its closest point (called
perogee) to the earth, approximately every 28 days.
Likewise, the
earth's elliptical orbit also causes variations in the sun's
pull on the tides as we move from the closest point to the
farthest point (called apogee) over the course of a year. And
just to complicate things even more, the moon's orbit is
inclined 5° to the earth's rotation. So the north/south
orientations of the bulge also varies between the northern and
southern hemisphere over this same 28-day orbital period.
As the moon
completes one orbit around the earth (about every 28 days),
there are two times in each orbit when the earth, moon and and
sun are inline with each other and two times when the earth,
moon and sun are at right angles.
When all three
are inline (around full and new moons), the combined effect of
the moon's and sun's pull on the earth's water is at its
greatest resulting in the greatest ranges between high and low
tide. This called a "spring" tide (from the water
springing or rising up).
Seven days after
either full or new moon, the earth, moon and sun are at right
angles to each other. At this time the pull of the moon and the
pull of the sun partially cancel each other out. The resulting
tide, called a "neap" tide, has the smallest range
between high and low tide
tsunamis
The word is
Japanese and means "harbor wave," because of the
devastating effects these waves have had on low-lying Japanese
coastal communities. The word tsunami (pronounced tsoo-nah'-mee)
is composed of the Japanese words "tsu" (which means
harbor) and "nami" (which means
"wave").Tsunamis are often incorrectly referred to as
tidal waves, but a tsunami is actually a series of waves that
can travel at speeds averaging 450 (and up to 600) miles per
hour in the open ocean.
Tsunamis are a
series of very long waves generated by any rapid, large-scale
disturbance of the sea. Most are generated by sea floor
displacements from large undersea earthquakes. Tsunamis can
cause great destruction and loss of life within minutes on
shores near their source, and some tsunamis can cause
destruction within hours across an entire ocean basin.
Credit:
Office of Naval Research (not
to scale)
Most tsunamis
occur in the Pacific region but they are known to happen in
every ocean and sea. Although infrequent, tsunamis are a
significant natural hazard with great destructive potential
Different sources provide energy
for these different types of motion. Surface and deep currents are powered by
solar radiation. The energy source for the tides is gravitational attraction of
the Earth and Moon. The Earth's internal heat provides energy for
tsunamis.
Wind
and the rotation of the Earth are important in determining the flow of
surface currents and local areas of upwelling and downwelling, but the
true driving force of deep water movement is thermohaline circulation.
Sometimes called the ocean conveyer belt, this mechanism is responsible
for bringing the oxygen that sustains life to the deepest reaches of the
sea, and in moving warmer waters from the tropics towards the poles.
Movement of this conveyer belt depends on sinking of cold water in
certain polar regions, thereby triggering the global thermohaline
circulation.
Oceanic
Circulation Patterns Source: Office of Naval Research. Oceanography
The
Gulf Stream merges into the North Atlantic Current. This warm water then
flows up the Norwegian coast, with a westward branch warming Greenland's
tip, at 60°NIt keeps northern Europe about nine to eighteen degrees
warmer in the winter than comparable latitudes elsewhere.
NASA
GSFC Satellite: TOPEX/Poseidon
Global warming
could alter this. Because freshwater is less dense than seawater,
increased precipitation, melting of polar glaciers and ice caps could
block the system by reducing the amount of cold water that sinks
downwards.
As
water travels through the water cycle, some water will become part of
The Global Conveyer Belt and can take up to 1,000 years to complete this
global circuit. It represents in a simple way how ocean currents carry
warm surface waters from the equator toward the poles and moderate
global climate. NASA Graphic
In
the Atlantic, warm, high-salinity water flows northward in the Gulf
Stream along the east coast of North America. Some of this water
continues northeastward in the North Atlantic Current toward Iceland and
Norway.
THE
ARCTIC HALOCLIINE—When sea ice forms, it releases salt into surface waters.
These waters become denser and sink to form the Arctic halocline—a layer of
cold water that acts as barrier between sea ice and deeper warmer water that
could melt the ice. (Illustration by Jayne Doucette, WHOI)
Off the coast of Greenland, a portion of the surface water
cools, becomes dense, and sinks. A further portion of surface water
continues into the Arctic Ocean before also cooling and sinking.
Together these sinking plumes off Greenland and in the Arctic form
"deep water" that plays an important role in global oceanic
circulation.
Sea
Water Salinity
Bigelow
Laboratory for Ocean Sciences Graphic
The
two most common elements in sea water, after oxygen and hydrogen, are
sodium and chloride. Sodium and chloride combine to form what we know as
table salt.
Sea water salinity is expressed as a ratio of salt (in grams) to liter
of water. In sea water there is typically close to 3.5 grams of
dissolved salts in each liter. It is written as 35‰ The normal range
of ocean salinity ranges between 3.3-3.7 grams per liter (33‰ -
37‰).
But as in weather, where there are ares of high and low pressure, there
are areas of high and low salinity. Of the five ocean basins, the
Atlantic Ocean is the saltiest. On average, there is a distinct decrease
of salinity near the equator and at both poles, although for different
reasons.
Near the equator, the tropics receive the most rain on a consistent
basis. As a result, the fresh water falling into the ocean helps
decrease the salinity of the surface water in that region. As one move
toward the poles, the region of rain decreases and with less rain and
more sunshine, evaporation increases.
Fresh water, in the form of water vapor, moves from the ocean to the
atmosphere through evaporation causing the higher salinity. Toward the
poles, fresh water from melting ice decreases the surface salinity once
again.
The saltiest locations in the ocean are the regions where evaporation is
highest or in large bodies of water where there is no outlet into the
ocean. The saltiest ocean water is in the Red Sea and in the Persian
Gulf region (around 40‰) due to very high evaporation and little fresh
water inflow.
The oceans vital
role in the Earth's carbon cycle
Life
in the ocean consumes and releases large quantities of carbon dioxide.
Across Earth's oceans, tiny marine plants called phytoplankton use
chlorophyll to capture sunlight during photosynthesis and use the energy
to produce sugars. Phytoplankton are the basis of the ocean food web,
and they play a significant role in Earth's climate, since they draw
down carbon dioxide, a greenhouse gas, at the same rate as land plants.
About half of the oxygen we breathe arises from photosynthesis in the
ocean.
The
above image shows the global biosphere. The Normalized Difference
Vegetation Index (NDVI) measures the amount and health of plants on
land, while chlorophyll a measurements indicate the amount of
phytoplankton in the ocean. Land vegetation and phytoplankton both
consume atmospheric carbon dioxide. Credit: SeaWiFS Project,
NASA/Goddard Space Flight Center, and ORBIMAGE
Because
of their role in the ocean's biological productivity and their impact on
climate, scientists want to know how much phytoplankton the oceans
contain, where they are located, how their distribution is changing with
time, and how much photosynthesis they perform. They gather this
information by using satellites to observe chlorophyll as an indicator
of the number, or biomass, of phytoplankton cells.
This
false-color map represents the Earth's carbon "metabolism"-the
rate at which plants absorbed carbon out of the atmosphere. The map
shows the global, annual average of the net productivity of vegetation
on land and in the ocean during 2002. The yellow and red areas show the
highest rates, ranging from 2 to 3 kilograms of carbon taken in per
square meter per year. The green, blue, and purple shades show
progressively lower productivity. Credit: NASA Goddard Space Flight
Center
Probably
the most important and predominant pigment in the ocean is chlorophyll-a
contained in microscopic marine plants known as phytoplankton.
Chlorophyll-a absorbs blue and red light and reflects green light. If
the ratio of blue to green is low for an area of the ocean surface, then
there is more phytoplankton present. This relationship works over a very
wide range of concentrations, from less than 0.01 ton early 50
milligrams of chlorophyll per cubic meter of seawater.
The ocean plays a vital dominant
role in the Earth's carbon cycle. The total amount of carbon in the ocean is
about 50 times greater than the amount in the atmosphere, and is exchanged with
the atmosphere on a time-scale of several hundred years. At least 1/2 of the
oxygen we breathe comes from the photosynthesis of marine plants. Currently, 48%
of the carbon emitted to the atmosphere by fossil fuel burning is sequestered
into the ocean. But the future fate of this important carbon sink is quite
uncertain because of potential climate change impacts on ocean circulation,
biogeochemical cycling, and ecosystem dynamics.
Carbon atoms are constantly being
cycled through the earth's ocean by a number of physical and biological
processes. The flux of carbon dioxide between the atmosphere and the ocean is a
function of surface mixing (related to wind speed) and the difference the
concentration of carbon dioxide in the air and water The concentration in the
ocean depends on the atmosphere and ocean carbon dioxide partial pressure which,
in turn, is a function of temperature, alkalinity (which is closely related to
salinity), photosynthesis, and respiration. Carbon is also sequestered for long
periods of time in carbon reservoirs (sinks) such as deep ocean and ocean
sediment.
Prior to the
Industrial Revolution, the annual uptake and release of carbon dioxide by the
land and the ocean had been on average just about balanced. In more recent
history, atmospheric concentrations have increased by 80 ppm (parts per million)
over the past 150 years. However, only about half of the carbon released through
fossil fuel combustion in this time has remained in the atmosphere, the rest
being sequestered the ocean.
Watching
Our Oceans JPL Video
The Ocean's Role
in Weather and Climate
The ocean is a
significant influence on Earth's weather and climate. The ocean covers 71% of
the global surface. This great reservoir continuously exchanges heat, moisture,
and carbon with the atmosphere, driving our weather patterns and influencing the
slow, subtle changes in our climate. The oceans influence climate by absorbing
solar radiation and releasing heat needed to drive the atmospheric circulation,
by releasing aerosols that influence cloud cover, by emitting most of the water
that falls on land as rain, by absorbing carbon dioxide from the atmosphere and
storing it for years to millions of years. The oceans absorb much of the solar
energy that reaches earth, and thanks to the high heat capacity of water, the
oceans can slowly release heat over many months or years. The oceans store more
heat in the uppermost 3 meters (10 feet) than the entire atmosphere.
The oceans and the
atmosphere form a closely linked "dynamic duo." Energy from the sun,
plant distributions, and greenhouse gasses in the atmosphere can affect
temperature and circulation patterns of this ocean-atmospheric duo.
The sun is Earth's
main source of energy. Solar energy is absorbed by both oceans and continents. Because
the oceans cover over 71% of Earth's surface and are darker than the
continents--they absorb more of the sun's energy. Oceans not only absorb
lots of energy from the sun--they can also store lots of solar energy in the
form of heat. And they can do this with very little change in temperature.
Sunlight warms the
surface of the ocean in the tropics. Wind-driven surface currents carry the heat
toward the poles. In the North Atlantic, the warm currents from the tropics feed
the North Atlantic Current shown in red in the figure. As the current flows
northward toward Norway and Greenland, it loses heat to the atmosphere and cools
down. In winter the water near Norway and Greenland gets so cold and dense it
sinks all the way to the bottom of the ocean. The cold bottom water feeds bottom
currents shown in blue and green. Eventually, mixing brings the bottom water
back to the surface in other parts of the ocean, sometime as far away as the
North Pacific. When the water gets to the surface, sunlight warms the water, and
the cycle starts over.
The alternating
influence of El Nino and La Nina are now well known These 3-5
year period disruptions in weather patterns are caused by the movement of warm
water in the tropical Pacific, and are now predictable up to a year in advance
because of a special monitoring network of ocean buoys maintained there.
Illustration by
Fritz Heide & Jack Cook, WHOI
The North Atlantic
Oscillation (NAO). Its "high index" state is shown above, this
corresponds to particularly high atmospheric pressure over the Azores, an
intense low over Iceland. Ocean winds are stronger and winters milder in the
eastern U.S. When the NAO index is low, ocean winds are weaker and the U.S.
winter more severe. Changes in ocean temperature distributions are also
observed.
The North Atlantic
Oscillation (NAO). When the NAO index is low, shown above, ocean winds are
weaker and the U.S. winter more severe. Changes in ocean temperature
distributions are also observed. Its "high index" state corresponds to
particularly high atmospheric pressure over the Azores, an intense low over
Iceland. Ocean winds are stronger and winters milder in the eastern U.S.
Sources:
NASA Oceanography, NOAA,Woods Hole Oceanographic Institute ,EPA, UNEP, U.S. Navy, U.S. Weather
Service
Data
compiled from The British Antarctic Study, NASA, Environment Canada,
UNEP, EPA and other sources as stated and credited Researched
by Charles Welch-Updated dailyThis Website is a project of the The
Ozone Hole Inc. a 501(c)(3) Nonprofit Organization
