OCEAN ZONES & BATHYMETRY Ref: Lesson 6 in textbook
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An ocean is a major body of saline water, and a principal
component of the hydrosphere. Approximately 71% of the Earth's
surface is covered by ocean, a continuous body of water that is
customarily divided into several principal oceans and smaller seas.
OCEAN ZONES
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CHARACTERISTICS More than half of this area is over 3,000
meters (9,800 ft) deep. Average oceanic salinity is around 35 parts
per thousand (ppt) (3.5%). Scientists estimate that 230,000 marine
life forms of all types are currently known, but the total could be
up to 10 times that number.
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WORLD OCEAN Though generally described as several 'separate'
oceans, these waters comprise one global, interconnected body of
salt water sometimes referred to as the World Ocean or global
ocean. This concept of a continuous body of water with relatively
free interchange among its parts is of fundamental importance to
oceanography.
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THE MAJOR OCEANIC DIVISIONS ARE DEFINED IN PART BY THE
CONTINENTS, VARIOUS ARCHIPELAGOS, AND OTHER CRITERIA. THESE
DIVISIONS ARE (IN DESCENDING ORDER OF SIZE): Pacific Ocean, which
separates Asia and Australia from the Americas Atlantic Ocean,
which separates the Americas from Eurasia and Africa Indian Ocean,
which washes upon southern Asia and separates Africa and Australia
Southern Ocean, which, unlike other oceans, has no landmass
separating it from other oceans and is therefore sometimes subsumed
as the southern portions of the Pacific, Atlantic, and Indian
Oceans, which encircles Antarctica and covers much of the Antarctic
Arctic Ocean, sometimes considered a sea of the Atlantic, which
covers much of the Arctic and washes upon northern North America
and Eurasia
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WORLD OCEAN The Pacific and Atlantic may be further subdivided
by the equator into northern and southern portions. Smaller regions
of the oceans are called seas, gulfs, bays, straits and other
names.
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ORIGIN OF OCEAN WATER One scientific theory about the origin of
ocean water states that as Earth formed from a cloud of gas and
dust more than 4.5 billion years ago, a huge amount of lighter
elements (including hydrogen and oxygen) became trapped inside the
molten interior of the young planet. During the first one to two
billion years after Earth's formation, these elemental gases rose
through thousands of miles of molten and melting rock to erupt on
the surface through volcanoes and fissures (long narrow
cracks).
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ORIGIN OF OCEAN WATER Within the planet and above the surface,
oxygen combined with hydrogen to form water. Enormous quantities of
water shrouded the globe as an incredibly dense atmosphere of water
vapor. Near the top of the atmosphere, where heat could be lost to
outer space, water vapor condensed to liquid and fell back into the
water vapor layer below, cooling the layer. This atmospheric
cooling process continued until the first raindrops fell to the
young Earth's surface and flashed into steam. This was the
beginning of a fantastic rainstorm that, with the passage of time,
gradually filled the ocean basins.
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ORIGIN OF OCEAN WATER Scientists calculate that this cosmic
rain adds one inch of water to Earth's surface every 10,000 to
20,000 years. This amount of water could have been enough to fill
the oceans if these comets have been entering Earth's atmosphere
since the planet's beginning 4.5 billion years ago.
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WHY IS THE OCEAN BLUE? A common misconception is that the
oceans are blue primarily because the sky is blue. In fact, water
has a very slight blue color that can only be seen in large
volumes. While the sky's reflection does contribute to the blue
appearance of the surface, it is not the primary cause. The primary
cause is the absorption by the water molecules' nuclei of red
photons from the incoming light, the only known example of color in
nature resulting from vibrational, rather than electronic,
dynamics.
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PHYSICAL PROPERTIES The total mass of the hydrosphere is about
1,400,000,000,000,000,000 metric tons which is about 0.023% of the
Earth's total mass. Less than 3% is freshwater; the rest is
saltwater, mostly in the ocean.
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TOPIC 1: BATHYMETRY :characteristics of the ocean floor The
surfaces of the Moon and Jupiter have been mapped more thoroughly
than the floor of the sea.
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NOT IN NOTES! - THE VAST UNKNOWN On January 7, 2005, only 400
miles from its base on Guam, the navy submarine USS San Francisco
was traveling about 35 mph when it slammed into an uncharted
mountain about 6,000 feet beneath the surface. One crew member died
and 23 others were injured.
http://www.strategypage.com/gallery/images/san_francisco_1.jpg
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OCEAN FLOOR The familiar landscapes of continents are mirrored,
and generally magnified, by similar features in the ocean basin.
The largest underwater mountains, for example, are higher than
those on the continents. Underwater plains are flatter and more
extensive than those on the continents. All basins contain certain
common features that include oceanic ridges, trenches, fracture
zones, abyssal plains, and volcanic cones.
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SEAFLOOR FEATURES
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1) CONTINENTAL SHELF Gently sloping land area along the edges
of continents
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2) CONTINENTAL SLOPE Steep slope leading from the edge of a
continent down to the seafloor
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3) CONTINENTAL RISE Hill of sediment at the bottom of the steep
slope near the edges of continents
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4) ABYSSAL PLAINS Abyssal plains are relatively flat areas of
the ocean basin with slopes of less than one foot of elevation
difference for each thousand feet of distance. They tend to be
found at depths of 4000-5000 meters. Oceanographers believe that
abyssal plains are so flat because they are covered with sediments
(clay, sand, and gravel) that have been washed off the surface of
the continents for hundreds of thousands of years. More extensive
in Atlantic and Indian Ocean because of constant river input of
sediments.
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5) OCEAN RIDGES Enormous mountain ranges, or oceanic ridges,
cover the ocean floor. The Mid-Atlantic Ridge starts at Greenland,
runs down the center of the Atlantic Ocean and ends at the southern
tip of the Africa. At that point, it stretches around the eastern
edge of Africa, where it becomes the Mid-Indian Ridge. Some
scientists say this is a single oceanic ridge that encircles Earth,
one that stretches a total of more than 40,000 miles.
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5) OCEAN RIDGES In most locations, oceanic ridges are 2,000
meters or more below the surface of the oceans. In a few places,
however, they actually extend above sea level and form islands.
Iceland, the Azores (about 900 mi. off coast of Portugal), and
Tristan de Cunha are examples of such islands.
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5) OCEAN RIDGES Running along the middle of an oceanic ridge,
there is often a deep crevice known as a rift, or median valley.
This central rift can plunge as far as 2,000 m below the top of the
ridge that surrounds it. Scientists believe ocean ridges are formed
when magma emerges from Earths interior, a process known as
seafloor spreading. Alfred Wegener developed continental drift
theory Which led to Harry Hesss proposal of seafloor spreading
Rifts may be the specific parts of the ridges where the magma
escapes.
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6) TRENCHES Trenches are long, narrow, canyon like structures,
most often found next to a continental margin. They occur much more
commonly in the Pacific than in any of the other oceans. The
deepest trench on Earth is the Mariana Trench, which runs from the
coast of Japan south and then west toward the Philippine Islandsa
distance of about 1,580 miles. The British naval vessel, Challenger
II surveyed the trench in 1951 and named the deepest part of the
trench, the "Challenger Deep".
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6) TRENCHES Its deepest spot is 11,033 meters below sea level.
Earthquakes and volcanic activity are commonly associated with
trenches.
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7) FRACTURE ZONES Fracture zones are regions where sections of
the ocean floor slide past each other, relieving tension created by
seafloor spreading at the ocean ridges. Ocean crust in a fracture
zone looks like it has been sliced up by a giant knife. The faults
in a zone usually cut across ocean ridges, often nearly at right
angles to the ridge.
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7) FRACTURE ZONES A map of the North Atlantic Ocean basin, for
example, shows the Mid-Atlantic Ridge traveling from north to south
across the middle of the basin, with dozens of fracture zones
cutting across the ridge from east to west.
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8) VOLCANIC CONES Ocean basins are alive with volcanic
activity. Magma flows upward from the mantle to the ocean bottom
not only through rifts, but also through numerous volcanoes and
other openings in the ocean floor. a) Seamounts are submarine
volcanoes and can be either active or extinct. b) Guyots are a type
of seamount. Extinct volcanoes that were once above sea level but
have since receded below the surface. As they receded, wave or
current action eroded the top of the volcano to a flat
surface.
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8) VOLCANIC CONES Seamounts and guyots typically rise about 0.6
miles above the ocean floor. One of the largest known seamounts is
Great Meteor Seamount in the northeastern part of the Atlantic
Ocean. It extends to a height of more than 4,000 m above the ocean
floor. Africa
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OCEAN ZONES The ocean can be divided into two basic regions: A.
The Pelagic Zone (anywhere in the water column) B. Benthic Zone
(the seafloor)
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PELAGIC ZONE The Pelagic Zone is further divided horizontally
into: 1. Neritic Zones Those near the coast. 2. Oceanic Zones Those
away from the influence of land.
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PELAGIC ZONE Can also be divided vertically into: A.Epipelagic
zone (0-200 meters) B.Mesopelagic Zone (2001000 meters)
C.Bathypelagic Zone (1000-4000 meters) D.Abyssalpelagic Zone
(4000-6000 meters) E.Hadalpelagic (6000 10,000 meters)
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BENTHIC ZONE Supralittoral (splash zone) rarely if ever covered
with water Intertidal/littoral Zone Regularly submerged and exposed
with the fluctuating tide levels Sublittoral (sub tidal) Zone which
extends to the edge of the continental shelf.
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OCEAN ZONES DIAGRAM
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PHOTIC ZONE Pelagic part of photic zone is also known as
epipelagic and covers the oceans from surface level to 200 m depth.
This is the region where photosynthesis can occur and therefore is
the most biodiverse. Since plants require photosynthesis, life
found deeper than this must either rely on material sinking from
above (see marine snow) or find another energy source; hydrothermal
vents are the primary option in what is known as the aphotic zone
(depths exceeding 200 m).
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HOW LIGHT PENETRATES THE OCEAN
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BENTHIC APHOTIC ZONES These correspond to the three deepest
zones of the deep-sea. The bathyal zone covers the continental
slope down to about 4,000 meters (13,000 ft). The abyssal zone
covers the abyssal plains between 4,000 and 6,000 m. Lastly, the
hadal zone corresponds to the hadalpelagic zone which is found in
the oceanic trenches.
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WATER DEPTH VS LIGHT PENETRATION Sunlight obviously cannot
penetrate beyond a certain depth in the ocean. Some organisms have,
however, evolved to cope with the absence of sunlight at great
depths. Plants require sunlight to carry on photosynthesisthe
process by which they convert carbon dioxide, water, and other
nutrients to simple carbohydrates to produce energy, releasing
oxygen as a byproduct. Below a depth of about 660 feet (200
meters), not enough sunlight penetrates to allow photosynthesis to
occur. The area of the ocean where photosynthesis occurs is known
as the euphotic zone (meaning "good light").
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LIGHT PENETRATION From the standpoint of living organisms, the
euphotic zone is probably the most important of all oceanic zones.
By some estimates, about two-thirds of all the photosynthetic
activity that occurs on Earth (on land and in the water) takes
place within the euphotic zone.
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LIGHT PENETRATION From 660 to 3,000 feet (200 to 900 meters),
only about 1 percent of sunlight penetrates. This layer is known as
the dysphotic zone (meaning "bad light"). Below this layer, down to
the deepest parts of the ocean, it is perpetual night. This last
layer is called the aphotic zone (meaning "without light"). At one
time, scientists thought that very little life existed within the
aphotic zone. However, they now know that a variety of interesting
organisms can be found living on the deepest parts of the ocean
floor.