15.1 An Overview of Oceans page 406
Vocabulary:
- lake
- oceanographer
- side-scan sonar
- sea level
Essential Questions:
1. What methods are used by scientists to study Earth’s oceans?
At the surface
- sonar (sound navigation and ranging) allows scientists to study the topography of the ocean floor.
To study depth, scientists send a sonar signal to the bottom and time how long it takes for the signal to bounce back. Sound travels at 1,500 m/s.
If it takes a “ping” 20 seconds from the time it is sent to the time it returns, how deep is the ocean in that location?
- Side-scan sonar is used to map large portions of the ocean floor. This method directs sound waves at an angle so that sides of hill and other topographic features can be mapped.
Floats that contain sensors are also used. The floats can monitor water temperature, salinity, and concentration of gases and nutrients as well as wave motion and speed of currents.
Nat Geo How Sonar works video
http://video.nationalgeographic.com/video/news/us-ocean-floor-mapping-vin 4:17
In the deep
- Submersibles or underwater vessels can be remotely operated or carry people.
Woods Hole Oceanographic Institute Alvin information
http://www.whoi.edu/main/hov-alvin/
Alvin videos:
Computers
Computers are used in both data collection and analysis. The data can be used to produce models tracking climate change, tsunamis, simulating tides, and distribution of coastal pollution.
2. How did the oceans form? page 408
Geologic clues tell us that the oceans have existed almost since the beginning of geologic history. Radioisotopes indicate that the Earth is 4.6 billion years old. “Glassy” lava flows form when lava cools very quickly as it does in water.
Where did the water come from?
Remote
- Comets are composed of ice and ice. When a comet collides with Earth, the ice melts into water.
- Meteorites studies indicate that meteorites contain 0.5 % water. Meteor bombardment released water
Local
- Volcanism during an eruption, significant quantities of gases including water vapor and carbon dioxide are released. A period of several mission years of volcanism occurred when the Earth was young. As Earth cooled, the water vapor condensed and the oceans formed. The oceans are thought to be 4 billion years old.
Volcanism continues to form water today but water is destroyed by UV radiation from the Sun. The two processes balance each other.
3. How is water distributed on Earth’s surface? 409
Distribution of Earth’s water
- What percent of Earth’s water is in oceans? _______
- What percent is fresh water? ______
- Of the fresh water, what percent is locked in glaciers? _______
If image is not clear use this link: http://upload.wikimedia.org/wikipedia/commons/7/7e/World_water_distribution.png
What might be an affect if icecaps and glaciers melt?
This link shows how glaciers have changed over time.
http://www.weather.com/science/environment/news/glaciers-then-and-now
Observe the views of Earth. How does the distribution of water int he northern hemisphere compare to the distribution of water in the southern hemisphere?
How will the difference affect the climate?
71 % of Earth’s surface is covered with water.
Of the 71%, 61 % is in the Northern hemisphere. What percent covers the Southern hemisphere?
15.2 Seawater
Vocabulary:
- salinity
- estuary
- temperature profile
- thermoclone
- pychnocline
Essential Questions:
1. What is the composition of sea water? page 413
Ocean water contains dissolved gases including oxygen and carbon dioxide as well as dissolved nutrients such as nitrates and phosphates.
The exact chemical composition varies by geographic location and depth.
Factors that affect the composition of sea water include:
- wave action
- vertical movements of water
- biological activity
Examine Figure 10 on page 413.
- How does oxygen level change with depth? Suggest a reason for the change.
- How do the oxygen levels differ between the North Pacific and the North Atlantic Ocean? What could explain the difference?
- Many organisms remove silica from the water in order to form their shells. Examine the graph of silica in seawater. What can you infer about how the population of these organisms changes with depth?
Salinity is the measure of the amount of dissolved salts in seawater.
Salinity is measured in grams of salt per 1,000 kg of water. The average salinity is 35 ppt (parts per thousand)
Convert 35 ppt to percent.
The most abundant salt in the sea is sodium chloride- ordinary table salt.
Variations in salinity
The average salinity of the sea is 35 ppt but varies from place to place.
Salinity is decreased by ___________ the amount of fresh water. What processes would decrease salinity?
Salinity is increased by ___________ the amount of fresh water. What processes would increase salinity?
Sources of salt in the sea
Geologic evidence shows us that the salinity of ancient seas was similar to today’s seas.
Sources are the same today as they were in ancient times. Volcanic activity added gaseous sulfur dioxide and chlorine gases which combined with the water to form sulfate and chlorine ions.
A second source is the weathering of crustal rocks which released sodium and calcium.
How do ions from weathered crustal rocks find their way to the oceans?
Removal of sea salts
Salts are continuously being added to sea water yet salinity does not increase because salts are also being removed.
Processes that remove salts are
1. evaporite formation- solids left behind when water evaporates from concentrated solutions of salt water.
2. biological activity organisms remove calcium ions from water to build shell, bones, and teeth
Review Video:
NASA Salt of the Earth 4:45
http://www.youtube.com/watch?v=EqpJZGyS4Bw
2. What are the physical properties of sea water?
3. How is ocean layering illustrated?
4. How do deep water masses form?
Ocean acidification
Dissolving sand dollar
mhttps://www.youtube.com/watch?v=wbkWkFu0XgY
Acid Test: The global challenge of Ocean Acidifcation
mhttps://www.youtube.com/watch?v=5cqCvcX7buo&feature=related
15.2 Sea water
15.3 Ocean Movements