Chapter 13

Section 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 Ocean Southern Ocean Arctic Ocean

Section 1 Earth’s Oceans Chapter 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 Floor Until 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 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.

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.

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.

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.

The Ocean Floor Mid-ocean Ridge Trench

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.

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

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

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

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

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 1000’s of km wide, and over 80,000-km long. Passes through all the Earth’s oceans.

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

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

Deep Sea Trenches 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 ocean because of variations in evaporation, circulation, and freshwater inflow.

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.

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 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.

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 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.