Download 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