Exploring the Oceans

1
Exploring the Oceans

• Chapter 13

2
The Earths Oceans

• Chapter 13
• Section 1

3
Divisions of the Global Ocean

• The largest ocean is the Pacific Ocean.
• The other oceans, listed from largest to
  smallest, are
• Atlantic Ocean
• Indian Ocean
• Southern Ocean
• Arctic Ocean

4
Section 1 Earths Oceans
Chapter 13
5
How Did the Oceans Form?

• About 4.5 billion years ago, there were no
  oceans.
• Sometime before 4 billion years ago, water vapor
  in the atmosphere condensed and fell as rain.
• The rain filled the deeper levels of Earths
  surface and the first oceans began to form.

6
How Did the Oceans Form?, continued
7
Exploring the Ocean Floor

• Until recently, the ocean floor was unexplored.
• The darkness, cold, and extreme pressure required
  new technology.
• Most scientists prior to the 1900s thought the
  ocean floor was flat, covered with layers of
  sediments washed in from the land.

8
HMS Challenger

• First dedicated exploration of the oceans (1872).
• Used a weighted line to find the depth of the
  water as they sailed.
• Slow and inaccurate, but it gave scientists an
  idea of the ocean floor.

9
Sonar

• Sound Navigation and Ranging.
• Invented in WWI to hunt submarines.
• Sound is bounced off the ocean floor to find the
  depth.
• The closer the bottom is, the quicker the echo
  returns.

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Studying the Ocean Floor

• Seeing by Sonar Scientists use sonar to
  determine the oceans depth.
• Oceanography via Satellite Scientists use
  images from the satellite Seasat to study ocean
  currents.
• Studying the Ocean with Geosat Scientists use
  the Geosat satellite to measure slight changes in
  the height of the oceans surface.

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Ocean Floor Mapping with Sonar
12
Revealing the Ocean Floor

• Regions of the Ocean Floor The two regions of
  the ocean floor are the continental margin and
  the deep-ocean basin.
• Underwater Real Estate The continental margin
  and the deep-ocean basin are subdivided into
  different areas and have different features.

13
Submersibles

• Specially designed submarines used by scientists
  to explore more than 1-km below the surface.
• Thick metal hulls protect the scientists from
  being crushed by the immense pressure.

14
The Ocean Floor
Mid-ocean Ridge
Trench
15
Continental Shelf

• Gently sloping, shallow part of ocean floor that
  extends outward from the continent.
• Varies from a few kilometers to over 1300-km from
  shore.
• Provides nutrient rich home to large numbers of
  fish.

16
Continental Slope

• Steeply slanting portion after the shelf.
• Bottom marks the edge of the continental crust.

17
Turbidity Currents

• Rapid moving currents that carry large amounts of
  sediments.
• Similar to landslides on land.
• Often cut canyons in the continental slope.

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Continental Rise

• Gentle slope at base of continental slope formed
  by accumulation of sediments that wash down.

19
Abyssal Plain

• Smooth parts of the deep ocean floor.
• Covered with fine grained muddy sediments (silt).
• Cover large areas of the ocean floor.

Mid-ocean ridge
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Mid-ocean Ridge

• Divergent boundary underwater, where new crust is
  being formed from magma deep in the mantle.
• Form underwater mountain ranges that seldom break
  the surface.
• Can be 1000s of km wide, and over 80,000-km
  long.
• Passes through all the Earths oceans.

21
Seamount

• Underwater volcanoes.
• If they reach the surface they form islands.

22
Volcanic Island Arcs

• These once underwater volcanoes grow so large
  they break the surface of the ocean.
• Associated with O-O convergent boundaries.

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Deep SeaTrenches

• Deepest part of the ocean.
• Many kilometers deeper than the surrounding
  abyssal plain.
• Very long (1000s of km), but fairly narrow
  (100-km across).
• Place where old crust is being subducted back
  into the mantle.
• Sign of convergent boundary.

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Characteristics of Ocean Water

• Dissolved Gases Nitrogen, oxygen, and carbon
  dioxide are the main gases dissolved in ocean
  water.
• Solids Sodium chloride, or table salt, is the
  most abundant dissolved solid in the ocean. Other
  solids are also found in ocean water.
• Ocean water is 3.5 salt.

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Characteristics of Ocean Water, continued

• Salinity is a measure of the amount of dissolved
  salts in a given amount of liquid.
• Changes in Salinity Climate and water movement
  affect salinity. Coastal water in cool, humid
  places has a low salinity. Slow-moving bodies of
  water have higher salinity than other parts of
  the ocean do.

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Ocean Salinity
Salinity varies in different parts of the ocean
because of variations in evaporation,
circulation, and freshwater inflow.
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Ocean Water and Density

• Salt water is denser than fresh water.
• Cold water is denser than warm water.
• Water of different densities will not mix easily.

In the resort town of Skagen you can watch an
amazing natural phenomenon. This city is the
northernmost point of Denmark, where the Baltic
and North Seas meet. The two opposing tides in
this place can not merge because they have
different densities.
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Characteristics of Ocean Water, continued further

• Temperature Zones The temperature of ocean water
  decreases as depth increases.
• Zones based on the amount of temperature change.
• Thermocline shows rapid temperature change.

29
Characteristics of Ocean Water, continued further
still

• Surface Temperature Changes Surface-zone
  temperatures vary with latitude and the time of
  year.
• Surface temperatures range from 1ºC near the
  poles to about 24 ºC near the equator.
• The surface zone is heated more in the summer.

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The Ocean and the Water Cycle

• The water cycle is the continuous movement of
  water from the ocean to the atmosphere to the
  land and back to the ocean.
• Driven by the sun.
• The ocean is an important part of the water
  cycle because nearly all of Earths water is in
  the ocean.

31
Oceans and Sunlight

• Sunlight will barely reach 150-m deep into the
  ocean.
• Below this it is always dark as night.
• Since plankton need sunlight, most sea life will
  be in this first 150 meters.

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A Global Thermostat

• The ocean regulates atmospheric temperatures.
• A Thermal Exchange The ocean absorbs and
  releases thermal energy much more slowly than dry
  land does.
• The circulation of warm water causes some
  coastal lands to have warmer climates than they
  would have without the currents.
• Ocean currents moderate the temperature of the
  planet by carrying warm water from the equator to
  the poles.

The Gulf Stream moderates the climate of Northern
Europe, making England and Scandinavia warmer
than you would expect from their latitude.
33
Oceans and Pressure

• As you increase depth the pressure increases.
• Increases at a rate of 10 times the air pressure
  at sea level per 100 meters of depth.
• Humans can safely dive to about 40 meters.
• Modern submarines can safely dive to only about
  600 meters (0.6-km).
• The average ocean depth is 3.8-km.