Transcript The Oceans
Oceanography
Oceanography
Oceanography is the scientific study of Earth’s Oceans
Oceanographers study:
Chemical composition
Temperature
Movement of ocean water
Seafloor sediments
Topography
Marine Life
Earth’s Water
Ocean’s contain 97% of water found on Earth
3% is located in frozen ice caps(Greenland, Antarctica)
Sea level has risen and fallen due to warming and
cooling of the Earth
Tectonic Processes
Earth’s Oceans
Earth is known as the
“Blue Planet”
71% of the surface is
covered by water
Average Depth is 3800
meters
Most landmasses are in
the Northern
Hemisphere
81% of the Southern
Hemisphere is water
Oceans and Seas
Oceans make up around 70% of the Earth’s surface
Divided into 4 Oceans:
Pacific-Largest
Atlantic-Between the Americas and Europe and Africa
Indian-3rd largest between Africa, Asia and Australia
Arctic-North of the Arctic Circle
Oceans and Seas
The Arctic and Antarctic
areas are covered by sea
ice
Ice is less dense than
water therefore ice
crystals form at the
surface
Parts break up in the
summer
Oceans and Seas
Seas are parts of the ocean
that are partially
landlocked
Black Sea
Mediterranean Sea
Caribbean Sea
Bering Sea
Seas that are completely
landlocked have a different
composition(More salt
water)
Caspian Sea
Aral Sea
Studying The Ocean
The Challenger-Late 1800’s, British research ship
Investigated ocean currents, water temperature, sediments,
topography
Used nets, dredges and other tools
Meteor- German ship in the 1920’s
Used sonar, first to map the Mid-Atlantic Ridge
Ocean Origin
The Earth is believed to be 4.6 Billion years old
The Ocean’s are thought to be about that old
Ancient lava flows suggest this
Formation of the oceans
One hypothesis suggests that water was released from
Earth’s interior by volcanism(out gassing)
As the Earth cooled this water vapor condensed and
filled the oceans
Formation of the Oceans
The second hypothesis
says that the water came
from comets
The impact of comets
releases water
Properties of Seawater
Properties of Seawater
Seawater
is a solution
of salts
in water
•Seawater
is a solution
of dissolved
salts dissolved
in
Salinity iswater
the concentration of all salts in seawater
•Salinity
Measured is
in the
grams
of salt per kilogram
water
concentration
of allofsalts
inor ppt
seawater
The average
salinity is about 35 ppt
•Measured in grams of salt per kilogram
of water or ppt
•The average salinity is about 35 ppt
Properties of Seawater
Most of the salt is NaCl which splits about in solution
Other ions: Sulfate, Magnesium, Calcium, Potassium,
Bicarbonate
Variations in Salinity
The highest salinity is found in subtropical regions(20-
30 latitudes)
The rate of evaporation exceeds the rate of
precipitation
Polar regions have lower salinities
Variations in Salinity
Higher salinities are found
in enclosed seas near
deserts such as the
Mediterranean Sea, Red
Sea
The Baltic Sea receives
fresh water from rivers,
lower salinity
Estuaries are partly
enclosed bodies of water at
the mouths of rivers. Very
low salinities(2-10 ppt)
Addition of Salt
The salinity of the oceans has remained fairly
consistent over time
Volcanoes release chlorine and sulfur dioxide which
dissolve in water
Weathering of continental rocks generates other ions
in seawater
Removal of Salt
When water evaporates ions stay behind and form
minerals
When organisms die ions in their shells, bones and
death accumulate on the ocean floor
Density
Pure water has a density of 1 g/ml
Seawater ranges from 1.02-1.03 g/ml
This is due to variations in salinity and temperature
Density increases with increasing salinity.
Density decreases with increasing temperature
The salinity can alter the freezing point (-2 C)
Light Absorption
Water absorbs light. Intensity decreases with depth
The absorption of different wavelengths varies as well
Marine animals may appear red near the surface but
look black at a depth of 10 meters
Temperature
The surface of the ocean
waters 15 degrees C(Is
warmer near the equator)
In the Polar regions the
water is cold from the
surface to the seafloor
After about 100 m of ocean
to about 1000 m the
temperature drops from
about 22 C to about 4 C
Temperature
The zone of rapidly decreasing of temperature with
depth is called the thermocline
After the thermocline the temperature is uniform at
roughly 4 degrees Celsius
Caused by differences in density
Water Masses
Cold, salty water comes from the Earth’s poles
Sea ice forms Salt ions are left behind Water
underneath sea ice is dense Sinks
The cold, salty water then migrates towards the
equator
Movement of Ocean Water
Oceans are always in constant movement caused by:
Variations in temperature
Variations in Density
Winds blowing across the water’s surface
Gravitational pull of the Moon and the Sun
Density Currents
The low temperatures of water at Earth’s poles are
responsible for the movement of seawater
Salts accumulate beneath the ice which increasing the
density of the seawater
The dense seawater sinks and moves toward the
equator. This is called a density current
Upwelling
Upwelling is the process where cold water from the
bottom of the ocean moves toward the surface
Occurs near continents.
Winds push water away from the land which is replaced
by deeper water which rises
Upwelling water is rich in nutrients which supports
marine life
Surface Currents
Surface currents are formed by Earth’s global wind
systems
In the tropics trade winds blow from east to west,
water moves in the same direction
Mid latitudes-Prevailing westerlies move from west to
east
Polar Regions-Winds move from east to west
Surface Currents
Gyres are large circular current systems that flow from
north to south
The Coriolis effect influences this
5 major gyres:
2 in the Pacific Ocean
2 in the Atlantic Ocean
1 in the Indian Ocean
Surface Currents
When a current encounters a landmass the water is
deflected away from the equator
As the warm current moves North it cools and turns
eastward
Gulf Stream-Flows along the east coast of North
America
Waves
A wave is a rhythmic movement that carries energy
through space or matter
Waves carry small amounts of water
Waves
Crest-Highest point of a wave
Trough-Lowest point of a wave
Wave Height-Distance between the crest and trough
Wavelength-The distance between two crests or
troughs
Factors influencing wave height:
Wind Speed
Wind Duration
Fetch
Waves
Waves lose energy when they reach shallow water due
to friction
As they slow they become higher and steeper
Breakers are collapsing waves
Tides
Sea level-Average height
of the ocean’s surface
Tides-Periodic rise and
fall of ocean waters
caused by the
gravitational attraction
of the Moon and Sun
Tides
One full tidal cycle takes about 24 Hours 50 Minutes.
This is due to the Moon rotating around the Earth
Spring Tides-When the Moon is full or new. High tides
are higher than usual, low tides are lower than usual
Neap Tides-The Earth, Moon and Sun form a right
angle. Lower tidal range
Shorelines
Shorelines are shaped by waves, tides and currents by
erosion and deposition
Ocean floor is shaped by tectonic processes
Erosion
Wave Refraction is the bending of a wave when it
reaches shallow water
This is caused by wave speed and water depth
A wave will reach a headland first and will bend
towards the headland
Erosion
Most of the energy is concentrated on headlands,
therefore they undergo erosion
This forms a wave cut platform at the base of a steep
cliff
Deposition
Coastal landforms are formed by sediment from
eroded land that are carried to the oceans by rivers
When waves and currents slow down these sediments
settle out and build coastal landforms
Beaches
Beaches
A beach is a sloping band of loose sediment at the
edge
of anisocean
•A
beach
a sloping band of loose sediment at
the
Theedge
size of the
sediments depends on the energy of the
an ocean
wavesize
thatof
deposited
it
•The
the sediments
depends on the
energy of the wave that deposited it
Longshore Current
Sediment is deposited in areas where the current slows
Sandbars often form and run parallel to most beaches
Result from waves breaking and dumping sediment
Longshore Current
A longshore current is
when a water approaches
the shore at an angle
Prevailing winds and
wave patterns influence
which direction it will
flow
Longshore currents
causes and is wash up
and down the beach in a
zigzag pattern
Longshore Current
Gaps in the sandbars
allow water to return to
the ocean. This forms a
rip current
Barrier Islands form
when sandbars form at
low tide and winds pile
up sand
Barrier Island
Spit-Forms when
longshore currents slow
due to increased water
depth
Baymouth-A spit that
has grown across the
mouth of a bay
Spit, Baymouth Bar
Artificial Protective Structures
Jetties-Walls of concrete
or boulders that extend
into the ocean on either
side of the entrance to a
harbor
Groins-Similar
structures to jetties that
trap sand on one side
and not the other
Artificial Protective Structures
Seawall-An embankment built along the shore to
protect the land from powerful waves
Erosion increases because waves are bounced back
with most of their original energy
Changes in Sea Level
Sea level has fluctuated over time
Rises in sea level after often attributed to melting
glaciers
If the polar ice sheets melted sea level would rise about
70 meters
Tectonic forces can cause a change in sea level
Sonar
Sonar-Emits sound pulses that the detect the depths of
the ocean floor
Side Scan Sonar-Sound pulses are directed toward the
seafloor at an angle.
Topographic features can then be mapped
Continental Margin
The continental margin is an area of continental crust
that lies below sea level. Continental crust is less dense
than oceanic crust
Continental Shelf
Continental Shelf is the portion of the continental
margin that lies closest to land
Average width is about 60 km
Most of this was exposed during the last ice age
Continental Shelf
The continental slope is where the ocean floor drops
steeply below the continental shelf
Continental Rise forms when sediments carried down
the continental slope settle at its base
Ocean Basins
Ocean basins are areas of the seafloor that are above
the oceanic crust
Ocean Basins
Abyssal Plains are smooth parts of the ocean basins
Sohm Abyssal Plain
Hatteras Abyssal Plain
Abyssal Plains sediment has been deposited over
millions of years
Ocean Basins
Deep Sea Trenches-Deep depressions in the ocean
basins
May stretch for thousands of kilometers
Mariana Trench
These are sites where tectonic plates converge
Ocean Basins
Mid Ocean Ridges-Chain of mountains that is broken
into segments by numerous cracks(fracture zones)
May emerge from the ocean’s surface as volcanic
islands
Form when magma rises along divergent plate
boundaries
Mid-Atlantic Ridge
Hydrothermal Vents
Hydrothermal Vents are
rifts in mid ocean ridges
that contain springs of hot
water
Seawater seeps into cracks
and is warmed by the
magma from the mantle
Black Smokers-Eject thick,
smoke like plumes of water
that can reach 350 degrees
Celsius
Ocean Basins
Seamounts are submerged mountains that are most
likely extinct volcanoes
Tablemounts (guyots) are submerged mountains with
flat tops
The lack of erosional processes cause these features to
last forever