Chapter 13

Chapter 13Section 1

Divisions of the Global Ocean

The largest ocean is the Pacific Ocean.

The other oceans, listed from largest to smallest, are: Atlantic Ocean Indian OceanSouthern Ocean Arctic Ocean

Section 1 Earth’s OceansChapter 13

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 Earth’s surface and the first oceans began to form.

How Did the Oceans Form?, continued

Exploring the Ocean FloorUntil recently, the ocean floor was unexplored.The darkness, cold, and extreme pressure

required new technology.Most scientists prior to the 1900’s thought the

ocean floor was flat, covered with layers of sediments washed in from the land.

HMS ChallengerFirst 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.

SonarSound 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.

Studying the Ocean Floor

Seeing by Sonar Scientists use sonar to determine the ocean’s 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 ocean’s surface.

Ocean Floor Mapping with Sonar

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.

SubmersiblesSpecially 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.

The Ocean Floor

Mid-ocean Ridge

Trench

Continental ShelfGently 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.

Continental SlopeSteeply slanting

portion after the shelf.

Bottom marks the edge of the continental crust.

Turbidity CurrentsRapid moving

currents that carry large amounts of sediments.

Similar to landslides on land.

Often cut canyons in the continental slope.

Continental RiseGentle slope at

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

Abyssal PlainSmooth parts of

the deep ocean floor.

Covered with fine grained muddy sediments (silt).

Cover large areas of the ocean floor.

Mid-ocean ridge

Mid-ocean RidgeDivergent 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 1000’s of km wide, and over 80,000-km long.

Passes through all the Earth’s oceans.

SeamountUnderwater

volcanoes.If they reach the

surface they form islands.

Volcanic Island ArcsThese once underwater volcanoes grow so

large they break the surface of the ocean.Associated with O-O convergent

boundaries.

Deep SeaTrenches

Deepest part of the ocean.

Many kilometers deeper than the surrounding abyssal plain.

Very long (1000’s of km), but fairly narrow (100-km across).

Place where old crust is being subducted back into the mantle.

Sign of convergent boundary.

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.

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.

Ocean Salinity

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

Ocean Water and DensitySalt 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.

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.

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.

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 Earth’s water is in the ocean.

Oceans and SunlightSunlight 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.

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.

Oceans and PressureAs 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.