The Ocean Floor

Chapter 13 Section 2

Studying the Ocean Floor

• Sonar- used on ocean surface
• Satellite- Seasat and Geosat- used in space

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Sonar

• Sound Navigation and Ranging
• Scientists send sound waves to the bottom of the ocean by ship.
• The sound waves bounce off the ocean floor and return to the ship.
• The deeper the ocean , the longer it takes for the sound waves to return.

SONAR-FYI

• Measuring Water Depth
• Today's oceanographers use sonar instruments to generate a sound signal that is bounced or "echoed" off the sea floor and then recorded on board the ship. The speed of sound in water is 1,500 m per second, four times faster than the speed of sound in air. By carefully measuring the round-trip time of the sound waves and taking into account the variables of temperature and salinity, the depth of the water and the distance to another object can be measured accurately.

Seasat

• Satellites send images to Earth that measure direction and speed of ocean waves

Seasat-1978

Geosat- Navy Satellite

• Military satellite
• Measures height of the ocean surface.
• Different underwater features affect the height of the water above them.

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The Ocean Floor

• Continental shelf
• Continental slope
• Continental rise
• Abyssal Plain
• Mid-ocean ridge
• Rift valley
• Ocean trench
• Seamounts

You do not have to write all of these, just make sure they are your headings.

• Continental shelf A
• Continental slope B
• Continental rise C
• Abyssal Plain E
• Mid-ocean ridge F
• Rift valley F
• Ocean trench H
• Seamounts D/G

A

A

B

D

E

F

G

H

C

Continental Margin

• Made up of:
• Continental shelf
• Continental slope
• Continental rise

Continental Shelf

• Begins at the shoreline
• Continues until the ocean floor starts to slope
• Depth can reach about 200 meters

Continental Slope

• Begins at edge of continental shelf
• Continues down to the flat part of the ocean floor
• Ranges between 200 meters to about 4000 meters

Continental Rise

• Base of continental slope
• Made of large piles of sediment

Deep Ocean Basin

• Made up of:
• Abyssal plain
• Mid-ocean ridge
• Rift valleys
• Seamounts
• Ocean trenches

Abyssal Plain

• Large, flat area of the ocean floor
• Covered in mud and remains of tiny marine organisms
• Average depth 4000 meters

Abyssal Plain

Mid-Ocean Ridge

• Underwater mountain ranges
• Form where tectonic plates pull apart
• Rising magma between the plates creates the ridge

Mid-Ocean Ridge

Rift Valley

• Zone between the plates
• In the rift valley, which can be 15 to 30 miles (24 to 48 kilometers) wide, new oceanic crust is being made, which means lots of seismic activity is happening.
• Hydrothermal vents were discovered in rift valleys.

Rift Valley

Ocean Trench

• Huge cracks on ocean floor
• Created by oceanic plate pushing beneath continental plate or another oceanic plate
• Deep-sea trenches are the deepest parts of the ocean.
• The deepest one, the Marianas Trench in the South Pacific Ocean, is more than 35,000 feet (10,668 meters), or almost 6.6 miles (10.6 kilometers) deep.
• A Navy-owned submarine, the Trieste, still holds the record for diving to the bottom of the deepest part of the Marianas Trench, the Challenger Deep, on January 23,1960.

Bioluminescence

• Scientists estimate that 90 percent of deep-sea species are bioluminescent .
• Bioluminescence is the production of visible light by living organisms.

Seamounts

• Mountains of volcanic material
• Formed when magma pushes it way through or between tectonic plates
• If seamounts build up they can become volcanic islands; Example: Hawaiian Islands
• Seamounts are usually 25 miles (40 kilometers) in diameter and can be 10,000 to 15,000 feet (3000 to 4500 meters) tall.

Seamounts

• Less than 0.1 percent of the world's seamounts have been explored to learn what species live on them, but many of the species that have been found so far are new to science.
• It has been estimated that more than 30,000 seamounts reaching more than 1,000 meters tall are found in the Pacific Ocean. Approximately 800 are in the Atlantic Ocean, and an unknown number exist in the Indian Ocean.
• They usually have volcanic origins.

Alvin

• Alvin, the world's first deep-sea submersible
• Three-person, self-propelling capsule-like submarine nearly eight meters long.
• Alvin has an operational maximum depth of about 4,000 meters.

Shinkai 6500- Japan

• Shinkai 6500, a Japanese research submarine built in 1989, can work at depths down to 6,400 m.
• World's deepest-diving manned research submarine.

Study Questions

• 1. The Hawaiian Islands form from what type of ocean feature?
• 2. Where is pressure the greatest or the most intense?
• 3. What is sonar?
• 4. Underwater mountain range?
• 5. Underwater volcano?
• 6. Feature of the ocean that is at the edge of a continent?
• 7. Production of visible light by an organism?
• 8. Besides organisms in the ocean, what other organism can you think of that produces visible light?
• 9. The flat part of the ocean floor?
• 10. What makes up the continental margin?
• 11. What makes up the deep ocean basin?
• 12. Where do tectonic plates pull apart or move away from each other?
• 13. Deepest part of the ocean?

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Answers

• 1. seamount
• 2. at the bottom of the ocean
• 3. Sound navigation and ranging- scientists send sound waves to the ocean floor and measure the time it takes for the sound waves to return
• 4. mid-ocean ridge
• 5. seamount
• 6. Continental shelf
• 7. Bioluminescence
• 8. fireflies/lightning bugs
• 9. abyssal plain
• 10. continental shelf, continental slope and continental rise
• 11.abyssal plain, mid-ocean ridge, rift valley, Ocean trench and seamount
• 12. Mid-ocean ridge
• 13. Ocean trench

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The Ocean Floor

• The continents lie on the continental plates. The edges of these plates are under water, and they form the continental shelves. These shelves slope outward very gently towards the ocean depths. In some places these shelves go out a long way, up to 900 miles: In other places the shelves are much narrower. These shelves are fairly smooth because debris from the land is falling onto them from the water. This debris contains nutrients washed down from the land, and these nutrients, plus the shallow water, contribute to the abundance of life forms near the continents.
•      Where the continental shelves end, there is a steep drop downwards. This is called the continental slope. It plunges down into the dark, cold waters of the ocean. At the bottom of the continental slope there is a an area that slopes gradually downward to blend into the abyssal plain. This is the bottom of the ocean as we think of it.
•      The ocean floor seems like a different world. There is no sun light down here. The water is very cold. The pressure of the weight of miles of water above this area would easily crush a submarine. Tiny flecks of material from the sunlit world float downward and eventually settle on the bottom. There is almost nothing to eat, and the animals that live here are few and far between. There are many different kinds of animals, but they are small and widely scattered. They are able to survive on very little.
•      However, it is not all silence and darkness here. The earth's crust is thinnest in the ocean basins, and volcanic eruptions are part of this environment.  Here and there isolated peaks called sea mounts rise above the flat abyssal plain. However, the most active part of deep ocean geology occurs in the deep sea trenches, where the ocean floor is spreading apart. Lava comes up through the fissures, building up mountains and deep sea vents, called smokers. The constantly up-welling lava pushes the sea floor away from the trenches and out towards the continents. When the sea floor reaches the continental plates, it subducts, or slides underneath them, carrying the cold rocky floor back into the hot mantle of the earth.
• �

Density, Salinity & Temperature

Density and Oceans

• Density is a measure of how much mass is contained in a given unit volume (density = mass/volume).
• Temperature, salinity and pressure work together to determine water density (weight of water divided by the amount of space it occupies).
• Cold, salty water is much denser than warm, fresher water and will sink below the less dense layer.
• The ocean waters can be divided into three layers, depending on their densities. Less dense waters form a top layer called the surface mixed zone. The temperature and salinity of this layer can change often because it is in direct contact with the air. For example, water evaporation could cause an increase in salinity, and a cold front could cause a drop in temperature.

Density and Oceans Cont…

• The next layer is the pycnocline, or transition zone. The density here does not change very much. This transition zone is a barrier between the surface zone and a bottom layer, allowing little water movement between the two zones.
• The bottom layer is the deep zone, where the water remains cold and dense. The polar regions are the only places where deep waters are ever exposed to the atmosphere because the pycnocline is not always present.

Density and Oceans Cont…

• circulation of surface waters of the ocean are driven by winds, the circulation of the deep waters are driven by density differences.
• Circulation in the depths of the ocean is referred to as thermohaline circulation.
• The deep ocean is layered with the densest water on bottom and the lightest water on top.
• Water tends to move horizontally throughout the deep ocean, moving along lines of equal density.
• Vertical circulation is limited because it is easier for water to move along lines of constant density (isopycnals) than across them.

Density and Oceans Cont…

Salinity

• Most of the salt in the oceans came from land.
• Over millions of years, rain, rivers, and streams have washed over rocks containing the compound sodium chloride (NaCl), and carried it into the sea.
• Some of the salt in the oceans comes from undersea volcanoes and hydrothermal vents (http://video.nationalgeographic.com/video/player/environment/habitats-environment/habitats-oceans-env/hydrothermal-vents.html)
• When water evaporates from the surface of the ocean, the salt is left behind. After millions of years, the oceans have developed a noticeably salty taste.
• Different bodies of water have different amounts of salt mixed in, or different salinities.
• Salinity is expressed by the amount of salt found in 1,000 grams of water. Therefore, if we have 1 gram of salt and 1,000 grams of water, the salinity is 1 part per thousand, or 1 ppt.

Salinity Cont…

• The average ocean salinity is 35 ppt.
• This number varies between about 32 and 37 ppt.
• Rainfall, evaporation, river runoff, and ice formation cause the variations. For example, the Black Sea is so diluted by river runoff, its average salinity is only 16 ppt.
• Freshwater salinity is usually less than 0.5 ppt.
• Water between 0.5 ppt and 17 ppt is called brackish. Estuaries (where fresh river water meets salty ocean water) are examples of brackish waters.
• Most marine organisms keep the salinity inside their bodies at about the same concentration as the water outside their bodies.
• If an animal that usually lives in salt water were placed in fresh water, the fresh water would flow into the animal through its skin. If a fresh water animal found itself in the salty ocean, the water inside of it would rush out.
• The process by which water flows through a semi-permeable membrane (a material that lets only some things pass through it) such as the animal's skin from an area of high concentration (lots of water, little salt) to an area of low concentration (little water, lots of salt) is called osmosis.

�Salinity cont…

• Halocline- vertical zone in the oceanic water column in which salinity changes rapidly with depth, located below the well-mixed, uniformly saline surface water layer.
• Especially well developed haloclines occur in the Atlantic Ocean, in which salinities may decrease by several parts per thousand from the base of the surface layer to depths of about one kilometre (3,300 feet). In higherﾉ

Temperature

• The Sun hits the surface layer of the ocean, heating the water up.
• Wind and waves mix this layer up from top to bottom, so the heat gets mixed downward too.
• The temperature of the surface waters varies mainly with latitude.
• The polar seas (high latitude) can be as cold as -2 degrees Celsius (28.4 degrees Fahrenheit) while the Persian Gulf (low latitude) can be as warm as 36 degrees Celsius (96.8 degrees Fahrenheit).
• Ocean water, with an average salinity of 35 psu, freezes at -1.94 degrees Celsius (28.5 degrees Fahrenheit). That means at high latitudes sea ice can form. The average temperature of the ocean surface waters is about 17 degrees Celsius (62.6 degrees Fahrenheit).

Temperature cont…

• Thermocline- a distinct zonation of waters based on temperature. In large bodies of water this is a natural process occurring between the air and wind influenced surface waters, which have relatively rapidly changing temperatures, with the colder, more constant temperature deeper waters.

Density, Salinity, Temperature & Organisms

Density, Temperature & Organisms

• Density of ocean water is about 1.026gm/cm^3. Which means anything below this will float and anything above this will sink.
• What do you think is the density of most phytoplankton, why?

Density, Temperature & Organisms

• As water becomes cold it sinks, which causes the under water currents in the oceans.
• This mixes the layers of water which allow food from the surface to reach the bottom. This along with upwelling and downwelling (the upward and downward motion of sub-surface water toward the surface and bottom of the ocean. This is often a source of cold, nutrient-rich water.
• Strong upwelling occurs along the equator where easterly winds are present. Upwelling also can occur along coastlines).
• This increases the productivity ( the amount of carbon available to the system as a result of photosynthesis) of the marine ecosystem.

Affect of Climate Change

• Increasing temperatures will cause distinct layers to form in the water, reducing the mixing and in turn lower productivity.
• Introduction of new species as a result of warmer water. Which compete with local species for space and food. (invasive species).
• http://www.whoi.edu/page.do?pid=12455

Salinity & Organisms

• All aquatic organisms must deal with the problem of maintaining internal homeostasis, a constant internal chemical environment in which that organism's enzymes can operate efficiently. This is largely a matter of osmoregulation- ability to move water in and out.
• Many marine organisms can get by with minimal osmoregulation since the oceans, are already a good environment; other marine organisms maintain their body fluids at ionic concentrations different from the surrounding ocean and must actively regulate ions. Freshwater also calls for active measures to maintain proper osmotic balance.

Salinity & Organisms cont..

• One method to avoid having to deal with osmotic balance is to cover the body with an impermeable membrane. Many aquatic organisms do just that, but this protection is necessarily incomplete, because three other processes involve intimate contact between a water-permeable body membrane and the surrounding fluid. In addition, these three other processes demand large surface areas in order to occur at sufficient rates to satisfy bodily needs.
• These three processes are, of course, respiration, absorption of food, and nitrogen excretion.
• Well, actually, only respiration is required of all aquatic organisms; plants do not ingest food (although they do need to take up plant nutrients), and plants do not have to excrete nitrogenous wastes, since they posses the chemical machinery needed to incorporate N into amino acids.