Transcript Slide 1

The Earth’s Oceans
The Water Planet
The Blue Planet
The world is dominated by
interconnected oceans. It just depends on
your viewpoint.
If we view the Earth from the
viewpoint of space, we can see that
most of the water is in the Southern
Hemisphere.
The Blue Planet
Nearly 71% of the Earth’s surface is
covered by the global ocean.
How Big is the Ocean
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The ocean covers about 360 million
square miles of the Earth’s surface.
Oceanographers divide the oceans into
four major ocean basins:
The Pacific
The Atlantic
The Indian
The Arctic
The Pacific Ocean
The Pacific Ocean is the largest ocean. It is
the largest single geographic feature on
the Earth. It comprises more than half of
the world’s oceans. With an average
depth of about 3,900 meters, it is the
deepest ocean in the world as well.
The Atlantic Ocean
The Atlantic Ocean is about half the size of
the Pacific Ocean. The Atlantic is slightly
shallower than the Pacific. Both the
Atlantic and Pacific Oceans are bounded
on their eastern and western sides by
continents.
The Indian Ocean
While the Indian Ocean is slightly smaller
than the Atlantic, it is about the same
depth. Unlike the Atlantic and Pacific, the
Indian Ocean is located almost entirely in
the southern hemisphere.
The Arctic Ocean
The Arctic Ocean accounts for only about
7% of the world’s oceans. It is also only
about one fourth as deep as the other
oceans of the world.
The World’s Oceans
• All the oceans are really one large body of
water.
• The average depth of the oceans is 3800m
or 3.8km.
• 97% of the water on Earth is found in the
oceans (only 3% of the water in the world
is freshwater).
Bathymetry
The study of the oceans topography is
called bathymetry.
Oceanographic History
The first serious look at the ocean came in
the 1870’s. The Challenger conducted an
6-year voyage to study the worlds oceans.
The Challenger sailed approximately
128,000 miles on its journey.
Current Technologies for Exploring
the Ocean
Today, there are various technologies
available to explore the ocean. These
include sonar, satellites and submersibles.
This allows modern scientists to explore
the ocean floor more efficiently and
accurately than ever.
Sonar
Sonar stands for Sound Navigation and
Ranging. Sound waves are bounced off
the ocean bottom and timed as they
arrive. The difference in arrival time can
be translating into a depth.
Sonar
Today, modern multibeam sonar sends
out multiple sound signals and receivers
to establish the depth of wide bands along
the ocean floor as opposed to narrow
points.
Side-scan Sonar
• Side-scan sonar is used to create an image of large areas of the
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sea floor. This tool is used for mapping the seabed for a wide
variety of purposes, including creation of nautical charts and
detection and identification of underwater objects and
bathymetric features.
Side scan uses a sonar device that emits fan-shaped pulses
down toward the seafloor across a wide angle perpendicular to
the path of the sensor through the water, which may be towed
from a surface vessel or submarine, or mounted on the ship's
hull.
The intensity of the acoustic reflections from the seafloor of this
fan-shaped beam is recorded in a series of cross-track slices.
When stitched together along the direction of motion, these
slices form an image of the sea bottom within the swath
(coverage width) of the beam.
The sound frequencies used in side-scan sonar usually range
from 100 to 500 kHz; higher frequencies yield better resolution
but less range.
Side-scan Sonar
Satellites
Satellites are able to compensate for
waves, tides, currents and atmospheric
effects to produce ocean surface and
topographic features images. Scientists
have discovered that the ocean is not flat.
Where seamounts and ridges occur the
ocean bulges up. Where undersea
canyons occur, the ocean has depressions.
SEAsat
Satellite Images
Submersibles
Submersibles are small underwater craft
capable of diving to great depths.
Submersibles such as Alvin and Sea Cliff II
can reach ocean depths of between 4,000
and 6,000 meters, respectively.
Submersibles
More modern versions of submersibles are
unmanned an operated with computers
and joy sticks. These submersibles
operate longer and cheaper because they
have no crews that require life support or
comforts.
Autosub
Ocean Topography
The ocean floor has been divided into
three major regions:
1. the continental margins
2. the ocean basin floor
3. the mid-ocean ridge
The Continental Margins
The continental margin includes the
continental shelf, the continental slope
and the continental rise. It does not
include the abyssal plain.
The Continental Margins:
The Continental Shelf
Continental shelves contain mineral
deposits, oil reservoirs, natural gas, and
huge sand and gravel deposits.
The Continental Margins:
The Continental Slope
The continental slope is located just seaward of the continental shelf.
Averaging only about 20 kilometers in width, it marks the boundary
between the continental and oceanic crusts.
The slope often has
deep channels cut into
them. These occur
at time when the
world’s oceans are
low and rivers cut
deeply into the exposed
sediment. Sometimes
large underwater landslides occur here that
create “turbidity currents”.
Turbidity Currents
Artificially created turbidity current
The Continental Margins:
The Continental Rise
• The continental rise marks the area of the
ocean floor where the incline of the sea
floor is reduced. The continental rise may
be hundreds of kilometers wide.
The Ocean Basin Floor
Between the continental margin and the
mid-ocean ridges, lies the ocean basin
floor. Some of the features of the ocean
floor basin include: deep-ocean trenches,
abyssal plains and seamounts and guyots.
Deep-ocean Trenches
Deep-ocean trenches are
long, narrow creases in the
ocean floor that form in the
deepest parts of the ocean.
Most of the trenches form
along the margins of the
Pacific and exceed 10,000
meters in depth. The
deepest know point on the
planet is located in the
Marianas Trench and is
over 11,000 meters deep.
These mark convergent
plate boundaries.
Abyssal Plains
Abyssal plains are huge expanses of
extremely flat sediments. They are
possibly the flattest places on the planet.
These plains are formed from sediment
carried by turbidity currents and settling
suspended sediments.
Seamounts and Guyots
Seamounts are undersea volcanic peaks
that dot the ocean floor. They are
volcanoes that have yet to reach the
surface.
Seamounts and Guyots
Once volcanic islands break the ocean’s
surface they begin to erode and form flattopped, once active structures called
guyots.
The Mid-Ocean Ridge
Mid-Ocean ridges
are found at the
center of most
ocean basins. It is
an interconnected
system of
underwater
mountains that
develop above
newly formed
ocean crust.
The Mid-Ocean Ridge
Mid-Ocean ridges are areas of seafloor
spreading or divergent plate boundaries
that we talked about earlier. This is where
new land is formed.
Hydrothermal Vents
• http://www.onr.navy.
mil/focus/ocean/habit
ats/vents1.htm
Seafloor Sediments
 Ocean-floor sediments can be classified
according to their origin into three broad
categories: terrigenous (lithogenous)
sediment, biogenous sediment, and
hydrogenous sediment.
 Terrigenous Sediment
• Terrigenous sediments consist primarily of
mineral grains that were eroded from continental
rocks and transported to the ocean.
Seafloor Sediments
 Biogenous Sediment
• Biogenous sediments consist of shells and
skeletons of marine animals and algae.
- Calcareous ooze is thick, common biogenous
sediment produced by dissolving calcium
carbonate shells.
- Siliceous ooze is biogenous sediment
composed of silica-based shells of single-celled
animals and algae.
 Hydrogenous
Sediment
• Hydrogenous sediment consists of minerals
that crystallize directly from ocean water
through various chemical reactions.
• One example is a manganese nodule.
Biogenous Sediments
Radiolaria
Foraminifera
Resources from the Seafloor
Energy Resources
 Oil and natural gas are the main energy
products currently being obtained from the
ocean floor.
 Gas Hydrates
• Gas hydrates are compact chemical structures
made of water and natural gas.
• Most oceanic gas hydrates are created when
bacteria break down organic matter in oceanfloor sediments.
Gas Hydrates
Resources from the Seafloor
 Other major resources from the ocean floor
include sand and gravel, evaporative salts,
and manganese nodules.
 Sand and Gravel
• The offshore sand-and-gravel industry is second
in economic value only to the petroleum industry.
Resources from the Seafloor
 Manganese Nodules
• Manganese nodules are hard lumps of
manganese and other metals (like cobalt, copper,
and iron) that precipitate around a small object.
 Evaporative Salts
• When seawater evaporates, the salt increases in
concentration until it can no longer remain
dissolved. When the concentration becomes
high enough, the salts precipitate out of solution
and form salt deposits.
• The most economically important salt is halite—
common table salt.
Manganese Nodules