The Oceans
It's obvious why Earth is called the "Blue Planet" as 71 percent of the surface is covered by
water, 97% of which is in oceans.
Oceans appeared on Earth between 3 and 4 billion years ago from which sprang life.
Ancient algal formations found in the water near Australia called stromatolites are thought to
have been the early source for oxygen in the atmosphere.
Oceans & Seas
1. Five principal oceans the Pacific, Atlantic, Indian, Southern and Arctic comprise the
"world ocean" that surround the Earth's continental land masses.
2. The Pacific Ocean is the largest covering 166 million square kilometers (64 million
square miles) of the surface with an average depth of 4200 meters (14,000 ft).
3. At nearly half the size, the Atlantic Ocean occupies 83 million square kilometers (32
million square miles) with an average depth of 3900 meters (13,000 ft).
4. Indian Ocean is slightly smaller at approximately 73 million square kilometers (28
million square miles).
5. The Southern Ocean surrounds Antarctica and was recognized in 2000 as an ocean by
the International Hydrographic Organization. It encompasses roughly 20.3 million
square kilometers (7.8 million square miles) with a typical depth between 4,000 and
5,000 meters (13,000 to 16,000 feet).
6. The Arctic Ocean is the smallest covering 13 million square kilometers (5 million square
miles) with an average depth of 930 meters (3250 ft). Some view the Arctic Ocean as a
sea rather than ocean because of its small size.
Water in Motion
Waves are undulations in the surface of a water body. Most of the waves that impact
the coastal zone originate in one of three ways.
The Tides: Cyclical rise and fall of the surface of the oceans. Caused by the gravitational
attraction of the Sun and moon on the Earth.
Tsunamis : sudden displacement of water, large ocean wave created from an earthquake or
volcanic eruption.
Wind Waves: created when air currents push along the water surface . Most of the waves that
impact the coastal zones and landforms are wind waves.
The Nature of Ocean Water
Sea water makes up the largest store of water in the hydrologic cycle.
It is comprised of nearly 60 chemical substances with common salt being the most abundant.
Ocean salinity varies from 32 - 37 parts per thousand. Salinity is lower near land and in the polar
regions.
A number of factors determine ocean salinity. Salinity is lower where freshwater rivers enter the
ocean.
In the North Pacific precipitation exceeds evaporation thus diluting ocean water. Water is more
saline in subtropical oceans where evaporation exceeds precipitation. The Atlantic ocean is the
most salty while the Arctic ocean is the least.
The oceans exhibit three vertical temperature zones, 1) a surface layer of water water,
2) a transition zone of decreasing temperatures with depth, and
3) the cold waters of the deep ocean. The zone of transition, known as the thermocline, is most
noticeable where surface water is warmest. Polar water may have no thermocline as the surface
temperature are very cold..
Origin of Oceans
http://www.youtube.com/watch?v=BvrzMBavDg&feature=PlayList&p=746AD498C993B957&index=31
Tides
Nearly all marine coastlines experience the rhythmic rise and fall of sea level called tides.
The daily oscillation in ocean level is a product of the gravitational attraction of the Moon and
Sun on Earth's oceans and varies in degree worldwide.
Tidal action causes coastal erosion and deposition as the shoreline migrates landward and
seaward.
Causes of Tides
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The gravitational attraction of the Sun is about half that of the Moon on the Earth.
Even though the Moon is much smaller in mass than the Sun it is closer and thus has a
greater influence on the Earth than does the Sun.
The gravitational pull of the Moon and the Sun stretches both solid and fluid surfaces of
the Earth. This creates a tidal bulge in the atmosphere, the oceans and to a very slight
extent the Earth's crust.
Figure 1. The two forces that result in tides
Courtesy NOAA (Source)
Gravity is not the only force responsible for a tidal bulge.
Inertia, the tendency of moving objects to continue moving in a straight line or stay motionless,
also affects the tidal bulge. As the gravitational force draws water closer to the Moon the inertial
force tries to keep it in place. The tidal bulge forms as the gravitation force exceeds the inertial
force on the near side. The gravitational force of the far (opposite) side is less because it is
farther away from the Moon. On this side, the inertial force exceeds the gravitational force. Here
the water attempts to keep going in a straight line, moving away from the Earth, creating another,
smaller bulge. Thus tidal bulge, is greatest on the side of the Earth facing the Moon or Sun ("near
side") simply because it's closer than the "far side" of the Earth.
During a high tide water moves landward as a flood current. During low tide water recedes
seaward as an ebb current.
Spring and Neap Tides
The Sun and Moon are said to be in conjunction with they
are aligned with the Earth.
The highest tides, and greatest gravitational attraction, occur
when the Sun and Moon are on the same side of the Earth
creating a spring tide. This occurs during the new moon
phase. A second lower spring tide occurs when the Sun
and Moon are on opposite sides of the Earth during the
full Moon phase.
A neap tide results when the Sun and moon are at right
angles to the Earth. There are two neap tides, at the firstquarter and third quarter phases of the Moon.
Courtesy Naval Meteorology Program and Oceanography Command "Restless Sea")
Tides:
Spring
http://www.youtube.com/watch?v=kHvBUDk7kkQ&feature=related
Seismic Waves (Tsunami)
A seismic wave or Tsunami is a devastating water wave generated by an undersea earthquake.
The sudden slippage of the ocean floor near the source of an earthquake can send a train of
seismic waves across the ocean. When the overriding plate along a subduction zone suddenly
breaks free it moves upward raising the sea floor and the water above. The waves move outward
in ever-expanding circles, nearly imperceptible in deep ocean water. As they approach land,
water recedes from the shore. This dramatic action often entices the curious to investigate. But
very shortly, a water rises rapidly and rushes landward.
http://www.youtube.com/watch?v=j9JDzBTwiig&eurl=http%3A%2F%2Fwww.uwsp.edu%2Fge
o%2Ffaculty%2Fritter%2Fgeog101%2Ftextbook%2Fcoastal_systems%2Fseismic_waves.html&
feature=player_embedded
Coastal and Marine Processes and Landforms
1. The various landforms of coastal areas are almost exclusively the result of the action of
ocean waves.
2. Wave action creates some of the world's most spectacular erosional landforms.
3. Where wave energy is reduced depositional landforms, like beaches, are created.
Properties of Waves
The source of energy for coastal erosion and sediment transport is wave action.
This wave energy is generated by the frictional effect of winds moving over the ocean surface.
It is important to realize that moving waves do not move the water itself forward, but rather the
waves impart a circular motion to the individual molecules of water. If you have ever gone
fishing in a boat on the ocean or a large lake you will have experienced this phenomenon. As a
moving wave passes beneath you, the boat rises and falls but does not move any distance across
the water body.
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Waves posses several measurable characteristics including length and height.
Wavelength is defined as the horizontal distance from wave crest to wave crest,
Wave height is the vertical difference between the wave's trough and crest.
Erosion, Transportation, and Deposition Along Coasts
A number of mechanical and chemical effects produce erosion of rocky shorelines by waves.
Depending on the geology of the coastline, nature of wave attack, and long-term changes in sealevel as well as tidal ranges, erosional landforms such as:
sea cliffs : A tall steep rock face
.
caves : A natural cavity or recess that is roughly positioned horizontally to the surface of the
Earth.
Sea arches, and, sea stacks, A steep pillar of rock located in the ocean a short distance
from the coastline. These landforms are created when waves erode through a thin
headland from both sides, can form.
Figure 10ac-4: Sea arches, Anse de l'Est, Ile aux Loups, Canada. (Source:
Natural Resources Canada - Terrain Sciences Division - Canadian
Landscapes).
Transportation by waves and currents is necessary in order to move rock particles eroded from
one part of a coastline to a place of deposition elsewhere. the upward movement of water onto
the beach (swash) occurs at an oblique angle. However, the return of water (backwash) is at
right angles to the beach, resulting in the net movement of beach material laterally. This
movement is known as beach drift. The endless cycle of swash and backwash and resulting
beach drift can be observed on all beaches.
Depositional landforms
Many kinds of depositional landforms are possible along coasts depending on the configuration
of the original coastline. Some common depositional forms are spits, bayhead beaches, barrier
beaches or bay-mouth bars.
Coasts
The characteristics of a coast depend on its geologic structure, initial topographic configuration,
and shoreline process that shape it. Submerged coasts form when river mouths are flooded due
to rising sea level or subsidence of land. A drop in sea level or rise in the land surface creates an
emergent coast. Depositional coasts have abundant depositional features like deltas, bars, spits
and reefs where new land has been built. Coral coasts are formed by biological rather than
physical processes.
This is a view of Dana Point taken (by Dr. C) from the north side of the point. List all of the
coastal landforms that you can identify in this picture:
Beach (in foreground)
Sea cliff
Marine terrace (skyline)
Wave-cut bench (part, extreme right side of photo)
Dana Point is a classic example of an emergent coastline. The marine terrace on
the top of the cliff represents an old beach level (in this case about 100,000 years
old). For an old beach to be this far above sea level, the land must have risen relative
to sea level (or sea level must have fallen relative to the land), which is the definition
of an emergent coastline.
This is an example of a submergent coastline. Barrier islands can only form when
sea level rises relative to the land (or the land sinks relative to sea level).
Point Reyes, California
Blue is water, and the brown lines on land are contour lines (lines of equal elevation). The
contour interval for this map is 100 feet
What type of coastal landform is present at location A? A sea cliff -- note the very steep
surface right next to the ocean.
Drakes Estero (B) is what type of estuary? A coastal plain estuary. Note the irregular
outline.
What type of landform is present at location C? A spit.
What type of estuary has formed in the location marked D? A bar-built estuary. Note that
the estuary is fairly narrow, and runs parallel to the coastline, separated from the open
ocean only by a narrow strip of sand.
Types of Estuaries
Radar image, part of California coast. Black areas are water.
(This image from the Space Shuttle Endeavour, launched on February 11, 2000)
What is the name of this bay? San Francisco Bay
San Francisco Bay is an example of a tectonic estuary
How did it form? Tectonic estuaries form when a block of bedrock is dropped down
relative to its surroundings by tectonic forces acting on the earth's crust. San
Francisco Bay formed when the block between two active faults was placed under
tension and slowly dropped down. The two faults are visible on the radar image. The
San Andreas Fault is indicated by arrows on the left, while the trace of the Hayward
Fault is indicated by the two arrows on the right side of the image.