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Oceanography is the
branch of Earth Science
that studies the Earth's
oceans and seas. It
covers a wide range of
topics, including marine
organisms and
ecosystem dynamics;
ocean currents, waves, and
geophysical fluid dynamics;
plate tectonics and the
geology of the sea floor; and
fluxes of various chemical
substances and physical
properties within the ocean
and across its boundaries.
Oceanography
Geological
Oceanography
Chemical
Oceanography
Biological
Oceanography
Physical
Oceanography
Geological oceanography,
or marine geology is the
study of the geology of the
ocean floor including plate
tectonics;
Chemical oceanography,
or marine chemistry is the
study of the chemistry of
the ocean and its
chemical interaction with
the atmosphere;
Biological oceanography
or marine biology is the
study of the plants,
animals and microbes of
the oceans and their
ecological interaction;
Physical oceanography or
marine physics studies
the ocean's physical
attributes including
temperature-salinity
structure, mixing, waves,
internal waves, tides and
currents.
The area of the Earth is
510 M sq km. of this
total, approximately
360 M sq km is
represented by oceans
and marginal seas.
Northern Hemisphere- 61% water, 39%
(Land Hemisphere)
land.
Southern Hemisphere- 81% water, 19%
(Water Hemisphere)
land
Northern
Hemisphere
Southern
Hemisphere
Oceans of the World
1.
2.
3.
4.
5.
Pacific Ocean
Atlantic Ocean
Indian Ocean
Southern Ocean
Arctic Ocean
Pacific Ocean
covers more than 166 million
square kilometers about 1/3 of the Earth surface
Atlantic Ocean
covers an area of 82 million sq km
Indian Ocean
covers an area of about 73 million sq km
Southern Ocean
large circumpolar body of water
totally encircling the continent of Antarctica
Arctic Ocean
the smallest ocean - more than five times
smaller than the Indian and Atlantic oceans
Geological Oceanography concerns
the nature of the earth beneath the
oceans: how ocean basins form and
are destroyed as the continents
separate and collide during the plate
tectonic cycle; how sediment forms,
accumulates, and is modified,
eroded and transported; and how
material exchange occurs at the
ocean floor.
Geological Oceanography
The Ocean Floor
Three Major Units
1. Continental margin
2. Ocean basin floor
3. Mid-ocean ridge
Geological Oceanography
Bathymetry is the measurement of
ocean depths and the charting of
the shape or topography of the
ocean floor.
1. Challenger Expedition
2. SONAR (Sound Navigation and
Ranging) or echo sounder
3. Multi-beam SONAR
4. Satellite altimetry
Geological Oceanography
Bathymetry
Echo sounding is a method of measuring depth
using powerful sound pulses. The time it takes
for the sound pulse to travel to the sea bed and
bounce back is a measure of the depth.
• The speed of sound in water is
1500 m/s. Thus, depth of any part
of an ocean is given by
d= ½ (1500 m/s X echo travel time)
Multibeam
systems can
provide more
accurate
measurements
than echo
sounders.
Multibeam
systems collect
data from as many
as 121 beams to
measure the
contours of the
ocean floor.
Bathymetry
Bathymetry
Satellite altimetry is an indirect way of measuring depth
and detecting sea floor features. Satellites measure the
sea surface height from their orbits by bouncing rapid
pulses of radar energy off the ocean surface. Sea floor
features like submerged mountains -- see figure below -have more mass than sea water.
This extra mass pulls the sea
surface into gentle “hills”
above the features. Thus we
can “see” features below the
surface by measuring the
variations in sea surface
height that these features
cause!
Continental Margin
Passive
Continental Margin
Active
Continental Margin
1. Continental shelf
2. Continental slope
3. Continental rise
Geological Oceanography
Continental Margins
There are two types of continental
margins:
1. Passive margins, also called
“Atlantic-type” margins, face the edges
of diverging tectonic plates. Very little
volcanic or earthquake activity is
associated with passive margins.
2. Active margins, known as
“Pacific-type” margins, are
located near the edges of
converging plates, where one
plate dives beneath another at an
oceanic trench, in the process of
subduction. Active margins are
therefore sites of extensive
volcanic and earthquake activity.
Passive VS. Active Continental Margins
The active margin has subduction at an oceanic trench
occurring next to it. The passive margin faces the
diverging plate boundary of the mid-ocean ridge.
Continental Margin
The CONTINENTAL MARGIN is the
transition to the deep ocean basin.
The margin belongs mostly to the
continent.
Geological Oceanography
PASSIVE CONTINENTAL MARGINS
are found along the
remaining coastlines.
Because there is no
collision or subduction
taking place, tectonic
activity is minimal and the
earth's weathering and
erosional processes are
winning.
Geological Oceanography
The shallowest portion of the
margin and the portion nearest to
the continent is the
CONTINENTAL SHELF. This
feature is simply an underwater
extension of the adjacent abovewater portion of the continent, the
COASTAL PLAIN.
Geological Oceanography
The CONTINENTAL SLOPE, as
its name implies, is the sloping
edge of the continent as it
merges into the deep ocean
basin.
Geological Oceanography
The CONTINENTAL RISE is a wedge
of sediment that has accumulated
at the base of the slope due to the
change in gradient from the
steeper slope to the virtually flat
abyssal plain. The continental rise
is named because of the “rise” of
the bottom seen by fathometers as
ships approach the continent.
Geological Oceanography
Passive Continental Margin
Geological Oceanography
An ACTIVE CONTINENTAL MARGIN is
found on the leading edge of
the continent where it is
crashing into an oceanic plate.
Geological Oceanography
Ocean Basin floor
1.Abyssal plains
2.Seamounts (tall volcanic
peaks)
3.Deep-ocean trenches
Geological Oceanography
The OCEAN BASIN FLOOR lies
between the continental margin
and the oceanic ridge. The size
of this region is almost 30% of
the Earth’s surface.
Geological Oceanography
ABYSSAL (a= without, byssus=
bottom) PLAINS are deep,
incredibly flat features. These
regions are likely the most level
places on Earth.
Geological Oceanography
SEAMOUNTS are isolated volcanic
peaks which may rise hundreds of
meters above the surrounding
topography.
GUYOTS or TABLEMOUNTS are
submerged, flat-topped
seamounts.
Geological Oceanography
DEEP-OCEAN TRENCHES are
long, relatively narrow creases
in the seafloor that form the
deepest parts of the ocean.
Challenger Deep (Mariana
Trench)- deepest part known
part of the world ocean
Geological Oceanography
Mid-Ocean Ridge
OCEANIC RIDGE or MID-OCEAN RIDGE
is topographically elevated feature
that is found near the center of the
most ocean basins. It is
characterized by extensive faulting
and numerous volcanic structures
that have developed on the newly
formed crust.
Geological Oceanography
The Ocean Floor
Geological Oceanography
Composition of Seawater
The most important
components of seawater that
influence life forms are
salinity, temperature,
dissolved gases (mostly
oxygen and carbon dioxide),
nutrients, and pH.
Chemical Oceanography
Seawater consists of
about 3.5 percent (by
weight) of dissolved
mineral substances that
are collectively termed
“salts”.
Chemical Oceanography
Salinity
The total amount of solid
material dissolved in water.
More specifically, it is the
ratio of the mass of dissolved
substances to the mass of the
water sample. It is expressed
in parts per thousand (0/00).
Chemical Oceanography
Thus, the average salinity of seawater
is 3.5% or 35 0/00.
Chemical Oceanography
Salinity map showing areas of high salinity (36 o/oo) in green,
medium salinity in blue (35 o/oo), and low salinity (34 o/oo) in
purple. Salinity is rather stable but areas in the North Atlantic,
South Atlantic, South Pacific, Indian Ocean, Arabian Sea, Red Sea,
and Mediterranean Sea tend to be a little high (green). Areas near
Antarctica, the Arctic Ocean, Southeast Asia, and the West Coast
of North and Central America tend to be a little low (purple).
Chemical Oceanography
Variations occur in ocean
salinity
The most common factor is the relative
amount of evaporation or
precipitation in an area. If there is
more evaporation than precipitation
then the salinity increases (since salt
is not evaporated into the
atmosphere). If there is more
precipitation (rain) than evaporation
then the salinity decreases.
Chemical Oceanography
Another factor that can change the
salinity in the ocean is due to a very
large river emptying into the ocean.
The runoff from most small streams and
rivers is quickly mixed with ocean water by
the currents and has little effect on salinity.
But large rivers (like the Amazon River in
South America) may make the ocean have
little or no salt content for over a mile or
more out to sea.
Chemical Oceanography
The freezing and thawing of ice also
affects salinity. The thawing of large
icebergs (made of frozen fresh water
and lacking any salt) will decrease
the salinity while the actual freezing
of seawater will increase the salinity
temporarily. This temporary increase
happens in the first stages of the
freezing of seawater when small ice
crystals form at about minus 2
degrees Centigrade.
Chemical Oceanography
These tiny, needle-like ice crystals
are frozen freshwater and the salts
are not part of them so the liquid
between these crystals becomes
increasingly salty to the point of it
being a brine. Eventually though,
as seawater freezes, the ice
crystals trap areas with brine and
the entire large piece of frozen
seawater (ice floe) is salty.
Chemical Oceanography
Many marine organisms are highly
affected by changes in salinity.
This is because of a process called
osmosis which is the ability of water
to move in and out of living cells, in
response to a concentration of a
dissolved material, until an
equilibrium is reached.
Chemical Oceanography
In general the dissolved material does
not easily cross the cell membrane so
the water flows by osmosis to form an
equilibrium. Marine organisms
respond to this as either being
osmotic conformers (also called
poikilosmotic) or osmotic regulators
(or homeosmotic).
Chemical Oceanography
Osmotic conformers have no mechanism
to control osmosis and their cells are the
same salt content as the liquid
environment in which they are found (in
the ocean this would be 35 o/oo salt). If a
marine osmotic conformer were put in
fresh water (no salt), osmosis would cause
water to enter its cells (to form an
equilibrium), eventually causing the cells
to pop (lysis).
Chemical Oceanography
If a marine osmotic conformer were put in
super salty water (greater than 35 o/oo
salt) then osmosis would cause the water
inside the cells to move out, eventually
causing the cells to dehydrate
(plasmolyze). These marine osmotic
conformers include the marine plants and
invertebrate animals which do not do well
in areas without a normal salinity of 35
o/oo.
Chemical Oceanography
Osmotic regulators have a variety of
mechanisms to control osmosis and the
salt content of their cells varies. It does not
matter what the salt content is of the water
surrounding a marine osmotic regulator,
their mechanisms will prevent any drastic
changes to the living cells. Marine osmotic
regulators include most of the fish,
reptiles, birds and mammals. These are
the organisms that are most likely to
migrate long distances where they may
encounter changes in salinity. An excellent
example of this is the salmon fish.
Chemical Oceanography
The fish is about 18 o/oo salt so in
seawater it tends to dehydrate and
constantly drinks the seawater. Special
cells on the gills (called chloride cells)
excrete the salt so the fish can replace
its lost water. When a salmon migrates
to fresh water its cells start to take on
water so the salmon stops drinking and
its kidneys start working to produce
large amounts of urine to expel the
water.
Chemical Oceanography
Temperature
Seawater temperature map showing areas of warmer water
in red and areas of cooler water is blue. White areas
represent ice.
Chemical Oceanography
The temperature of seawater varies with the
amount of sun that hits that area. This includes
the length of time as well as the angle of the
sun's rays. The longer the time and the more
direct the rays of the sun fall on the ocean, the
greater the temperature of seawater. Thus,
tropical areas that get more year-round sun and
more direct sun (almost 90 degrees, straight
down for most of the year at noon) have warmer
surface waters than polar areas that may have
no sun at all for several months each year and
then very steep angles of the sun's rays (never
directly overhead at noon).
Chemical Oceanography
Knowing this about ocean water helps us
understand that surface ocean
temperatures are warm in the tropics
(up to 30 or more degrees C) and cooler
at the poles (down to -2 degrees C).
But, when we look below the surface
we find that the oceans are also
vertically stratified and marine
scientists recognize a basic three
layered ocean - the upper mixed layer,
the main thermocline, and deep
(bottom) water.
Chemical Oceanography
The upper mixed layer is all one
temperature but that temperature can
vary from -2 degrees C, at the poles, to
+30 degrees C, in the tropics. It all
depends on the latitude and effects of the
sun's heat and may be highly seasonal.
The depth of this layer can be anything
between the surface and 200 meters deep
- usually the 200 meter depth is near the
equator. The volume of this upper mixed
layer is only about two percent of the
volume of the ocean water.
Chemical Oceanography
The main thermocline is an area of rapidly
decreasing temperature with depth. This
changes with latitude and may begin at 200
meters (the bottom of the mixed layer) in the
tropics where it may end at close to 1,000
meters (or anywhere above that depending on
the strength of the sun). It may also begin right
at the surface of the ocean in high temperate
areas and extend to a variety of depths. This
layer shifts up and down with the seasons in the
temperate areas. The main thermocline
comprises only 18 percent of the volume of the
ocean water.
Chemical Oceanography
Deep (or bottom) water is always one cold
temperature ranging between -2 to +5 degrees
C. It is below the main thermocline (at the
bottom of the thermocline there is no longer a
decrease in water temperature with depth ... it is
all one cold temperature). It is not affected by
the seasons. This layer has most of the
seawater and comprises close to 80 percent of
all ocean water by volume. It is under the
tropical areas, most temperate areas when there
is a main thermocline, and is all the way to the
surface in the polar areas (where there is no
thermocline).
Chemical Oceanography
Chemical Oceanography
Seawater temperature affects
marine organisms by changing
the reaction rates within their
cells. Although each species has
a specific range of temperature
at which it can live, the warmer
the water gets the faster the
reactions and the cooler the
water the slower the reactions.
Chemical Oceanography
An organism's response to water temperature is
considered to be cold blooded (or poikilothermic)
or warm blooded (homeothermic) depending on
their ability to control their internal body
temperature. If any species is moved out of its
temperature tolerance range it may die in a short
time although temperatures on the cool side of
the range are easier for organisms to tolerate
than temperatures on the warm side because
cell reactions just slow down in the cold but may
speed up over six times the normal levels for
each 10 degrees C of heat.
Chemical Oceanography
Cold blooded (poikilothermic) marine
organisms lack any temperature
controls. These include marine plants,
invertebrates, most fish and marine
reptiles. These species each have their
specific temperature tolerance range
within which they must live (some are
adapted to polar temperatures, some to
tropical temperatures). Some have a
narrow range (and are thus very restricted)
and some have a wide range (and are
thus less restricted).
Chemical Oceanography
Warm blooded (homeothermic) marine
organisms have some type of internal
temperature controls to maintain a
constant body temperature. These
organisms include a few fish, all sea birds
and mammals. This ability allows these
warm blooded marine species to migrate
over vast distances through various
temperatures without problems and
include some of the animals on Earth with
the longest migrations.
Chemical Oceanography
Density
Temperature, salinity and pressure affect
the density of seawater. Large water
masses of different densities are important
in the layering of the ocean water (more
dense water sinks). As temperature
increases water becomes less dense. As
salinity increases water becomes more
dense. As pressure increases water
becomes more dense.
Chemical Oceanography
A cold, highly saline, deep mass of
water is very dense whereas a
warm, less saline, surface water
mass is less dense. When large
water masses with different
densities meet the denser water
mass slips under the less dense
mass. These responses to
density are the reason for some
of the deep ocean circulation
models.
Chemical Oceanography
Dissolved Gases
The concentration of dissolved oxygen and
carbon dioxide are very important for
marine life forms. Although both oxygen
and carbon dioxide are a gas when
outside the water, they dissolve to a
certain extent in liquid seawater. Dissolved
oxygen is what animals with gills use for
respiration (their gills extract the dissolved
oxygen from the water flowing over the gill
filaments). Dissolved carbon dioxide is
what marine plants use for photosynthesis.
Chemical Oceanography
The amount of dissolved gases varies
according to the types of life forms in
the water. Most living species (both
plants and animals) need oxygen to
keep their cells alive and are
constantly using it up. Replenishment
of dissolved oxygen comes from the
photosynthetic activity of plants
(during daylight hours only) and from
surface diffusion (to a lesser extent).
Chemical Oceanography
If there are a large number of plants in
a marine water mass then the oxygen
levels can be quite high during the
day. If there are few plants but a large
number of animals in a marine water
mass then the oxygen levels can be
quite low. Oxygen is measured in
parts per million (also called ppm)
and levels can range from zero to
over 20 ppm in temperate waters.
Chemical Oceanography
It only reaches 20 when there are a lot
of plants in the water, it is very sunny
with lots of nutrients, and the wind is
whipping up the surface into a froth.
In any water mass there is a
maximum amount of dissolved gas
that can be found (after which the gas
no longer dissolves but bubbles to the
surface).
Chemical Oceanography
This maximum amount increases
with a decrease in temperature
(thus cold water masses can hold
more dissolved gases ... but they
can also have none if it has been
used up). So, just because a
water mass is cold it does not
mean it has a lot of dissolved
gases.
Chemical Oceanography
This concept is a little tricky but just
remember that the amount of
dissolved gases in seawater depends
more on the types of life forms (plants
and animals) that are present and
their relative proportions.
Chemical Oceanography
Dissolved Nutrients
Fertilizers, like nitrogen (N),
phosphorous (P), and potassium (K),
are important for plant growth and are
called 'nutrients.' The level of dissolved
nutrients increases from animal feces and
decomposition (bacteria, fungi). Surface
water often may be lacking in nutrients
because feces and dead matter tend to
settle to the bottom of the ocean. Most
decomposition is thus at the bottom of the
ocean.
Chemical Oceanography
In the oceans most surface water is
separated from bottom water by a
thermocline (seasonal in temperature
and marginal polar regions, constant in
tropics) which means that once surface
nutrients get used up (by the plants
there) they become a limiting factor for
the growth of new plants. Plants must
be at the surface for the light. Nutrients
are returned to surface waters by a
special type of current called
'upwelling' and it is in these areas of
upwelling that we find the highest
productivity of marine life.
Chemical Oceanography
Silica and iron may also be considered
important marine nutrients as their
lack can limit the amount of
productivity in an area. Silica is
needed by diatoms (one of the main
phytoplanktonic organisms that forms
the base of many marine food chains.
Iron is just recently being discovered
to be a limiting factor for
phytoplankton.
Chemical Oceanography
pH
pH is a measure of the acidity or
alkalinity of a substance and is one
of the stable measurements in
seawater. Ocean water has an
excellent buffering system with the
interaction of carbon dioxide and
water so that it is generally always at
a pH of 7.5 to 8.5.
Chemical Oceanography
Neutral water is a pH of 7 while acidic
substances are less than 7 (down to
1, which is highly acidic) and alkaline
substances are more than 7 (up to
14, which is highly alkaline). Anything
either highly acid or alkaline would kill
marine life but the oceans are very
stable with regard to pH. If seawater
was out of normal range (7.5-8.5)
then something would be horribly
wrong.
Chemical Oceanography
In summary, the salinity and pH of
seawater are relatively stable
measurements whereas temperature,
dissolved oxygen, and nutrients may
vary.
Chemical Oceanography
Ocean Life
A wide variety of organisms inhabit the
marine environment. These organisms
range in size from microscopic bacteria
and algae to blue whales.
Most organisms live within the sunlit surface
waters of the ocean. Strong sunlight
supports photosynthesis.
Biological Oceanography
Classification of Marine
Organisms
Marine organisms can be classified to where
they live (their habitat) and how they move
(their mobility)
Organisms that inhabit the water column can
be classified as either plankton (floaters)
or nekton (swimmers). All other organisms
are benthos (bottom dwellers).
Biological Oceanography
Plankton
Plankton consist of any drifting organisms
(animals, plants, or bacteria) that inhabit
the pelagic zone of oceans, seas, or
bodies of fresh water. Plankton are defined
by their ecological niche rather than their
genetic classification. They provide a
crucial source of food to aquatic life.
Biological Oceanography
Plankton are primarily divided into broad functional
(or trophic level) groups:
1. Phytoplankton (from Greek phyton, or plant),
autotrophic, prokaryotic or eukaryotic algae that
live near the water surface where there is
sufficient light to support photosynthesis. Among
the more important groups are the diatoms,
cyanobacteria and dinoflagellates.
2. Zooplankton (from Greek zoon, or animal),
small protozoans or metazoans (e.g.
crustaceans and other animals) that feed on
other plankton and telonemia. Some of the eggs
and larvae of larger animals, such as fish,
crustaceans, and annelids, are included here.
Biological Oceanography
3. Bacterioplankton, bacteria and archaea,
which play an important role in
remineralizing organic material down the
water column (note that the prokaryotic
phytoplankton are also bacterioplankton).
Biological Oceanography
Nekton refers to the aggregate of actively
swimming aquatic organisms in a body of
water (usually oceans or lakes) able to
move independently of water currents.
Nekton are contrasted with 'plankton'
which refers to the aggregate of passively
floating, drifting, or somewhat motile
organisms occurring in a body of water,
primarily comprising tiny algae and
bacteria, small eggs and larvae of marine
organisms, and protozoa and other minute
predators.
Biological Oceanography
Oceanic nekton comprises animals from
three phyla
• Chordates form the largest contribution,
these animals are supported by either
bones or cartilage.
• Mollusks are animals like octopodes and
squids.
• Arthropods are animals like shrimp.
Biological Oceanography
Biological Oceanography
Ocean Circulation
A. Surface Circulation
*Currents are masses of ocean water
that flow from one place to another.
Surface currents develop from friction
between the ocean and the wind that
blows across its surface. These are
relatively permanent phenomena and
considered to be responses to
local/seasonal variations
Physical Oceanography
Physical Oceanography
Surface currents, shown below, are driven
by the winds. Warm water is red and cold
water is blue. The Trade Winds propel ocean
water westward along the equator, and
when it strikes a continent, it is diverted
poleward. However, a narrow return flow
also occurs along the equator. In midlatitudes the currents are driven eastward
by the Westerlies. The opposing wind belts
cause currents in all the ocean basins to
form gyres, or giant loops.
Physical Oceanography
Ocean Circulation Patterns
Gyres are large whirls of water within an
ocean basin (North Pacific, South Pacific,
North Atlantic, South Atlantic, Indian
Ocean).
The center of each gyre coincides with the
subtropics (30 degrees N or S from the
equator)
Subtropical gyres in NH rotate clockwise
while those in the SH rotate the other way
because of Coriolis effect.
Physical Oceanography
The Gulf Stream
• Most studied current
• Flows northward along the East
Coast of the United States
• So named because it carries
warm water from the Gulf of
Mexico and because it is narrow
and well-defined like a stream
Physical Oceanography
• Today, satellites reveal that
warm waters of the Gulf Stream
has many complexities including
prominent bends called
meanders which produce large
circular eddies that spin off from
the main current and can last for
up to two years before
dissipating.
 Ocean currents have an important
effect on climates.
Physical Oceanography
• Aside from producing
currents, winds also cause
vertical water movements.
• The rising of cold water from
deep layers to replace warm
surface water is called
UPWELLING, a common
wind-induced vertical
movement.
Physical Oceanography
• Coastal upwelling happens along
the west coasts of continents.
• As the surface layer moves away
from the coast, it is replaced by
water that “upwells” from below
the surface. This slow upward
movement from depths of 50 to
300 meters brings water that is
cooler than the original surface
water and results in lower
surface water temperatures near
the shore.
Physical Oceanography
Deep-Ocean Circulation
• Has a significant vertical component
that accounts for the thorough
mixing of deep water masses
• This component of ocean circulation
is a response to DENSITY
DIFFERENCES among water masses
that cause denser water to sink and
spread out beneath the surface.
Physical Oceanography
• Since density difference is caused by
variations in temperature and salinity,
deep-ocean circulation is also referred as
THERMOHALINE CIRCULATION.
• Most water involved in deep-ocean
currents begins in high latitudes. Surface
water becomes cold and its salinity
increases as sea ice forms. When this
surface water becomes dense enough, it
sinks, initiating deep ocean currents. Once
this water sinks, it is removed from the
physical processes that increased its
density in the first place, so its
temperature and salinity remain largely
unchanged.
Physical Oceanography
• Near Antarctica, surface
conditions create the highestdensity water in the world. This
cold saline water brine slowly
sinks to the seafloor, where it
moves throughout the ocean
basins in sluggish currents. After
sinking from the surface to the
ocean, deep waters will not
reappear at the surface for an
average of 500 to 2000 years.
Physical Oceanography
• A simplified model of ocean circulation
is similar to a conveyor belt that travels
from the Atlantic through the Indian
and pacific Oceans and back again. In
this model, warm water in the ocean’s
upper layers flows poleward, converts
to dense water and return s
equatorward as cold deep water that
eventually upwells to complete the
circuit. As this “conveyor belt” moves
around the globe, it influences the
global climate by converting warm
water to cold and liberating heat to the
atmosphere.
Physical Oceanography
Ocean in Motion: Waves
• As wind passes over the water's surface,
friction forces it to ripple. The strength of
the wind, the distance the wind blows
(fetch) and the length of the gust (duration)
determine how big the ripples will become.
• Waves are divided into several parts:
crest, trough, wavelength, wave height
and wave period.
Physical Oceanography
Physical Oceanography
• The crest is the highest point on a wave,
while the trough, or valley between two
waves, is the lowest point. Wavelength is
the horizontal distance, either between
the crests or troughs of two consecutive
waves. Wave height is a vertical distance
between a wave's crest and the next
trough. Wave period measures the size
of the wave in time. A wave period can be
measured by picking a stationary point
and counting the seconds it takes for two
consecutive crests or troughs to pass it.
Physical Oceanography
• In deep water, a wave is a
forward motion of energy, not
water. In fact, the water does
not even move forward with a
wave. If we followed a single
drop of water during a passing
wave, we would see it move in a
vertical circle, returning to a
point near its original position at
the wave's end.
Physical Oceanography
•These vertical circles are
more obvious at the
surface. As depth
increases, their effects
slowly decrease until
completely disappearing
about half a wavelength
below the surface.
Physical Oceanography
The water droplet moves in a vertical circle as the
wave passes. The droplet moves forward with the
wave's crest and backward with the trough.
References:
Tarbuck, Edward J. et al. 2003. 10th edition
Earth Science. Pearson Education, Inc.,
USA.
http://www.onr.navy.mil/focus/ocean/motion/
currents1.htm