Oceans Chapter 2 - The Ocean Floor
How many oceans are in the world ?
5 Oceans
Active Margin
An active continental margin is found on the leading edge of the continent where it is crashing into an oceanic plate.
World's Largest and deepest ocean?
Pacific Ocean (Тихий)
What is Hydrothermal vents (выход)?
Water entering cracks An opening in the sea floor out of which heated mineral-rich water flows.
Mid - ocean ridge
- 2500 meters above seafloor - 1000 km wide - Rift Valley - Pillow lavas - Hydrothermal vents - Transform faults
Echo sounder
- After Titanic SONAR was invented. - Sends a sound signal (ping) downward and listen for echo from the sea floor. - Speed of sound is known in seawater and varies little as the temperature and salinity of the water changes. - Time between pulse and return of the echo, when multiplied by speed of sound in seawater, is twice the ocean depth.
What are 3 Ocean Provinces?
- Continental Margin - Deep ocean basins - Mid - ocean ridge (Look at the provided diagram)
Continental Margin
- Continental shelf - almost flat and featureless - Shelf break - Continental slope - increases in slope angle - Continental rise - transition zone (See the provided diagram) - Canyons - V shaped deep submarine valleys - Passive VS Active Margins
What is a Fathom?
- Length between the outstretched arms of a sailor - 6 feet - Usually shown on rope with knots every 6 feet to indicate a fathom. (Look at the diagram)
How is an ocean created?
- Ocean floor splits in 2 and is carried away from axis Replaced by upwelling of volcanic material that fills the void (пробелы) with the new strips of sea floor - At the same time, ocean floor is being destroyed at deep ocean trenches?
Sounding
- Originally measured by letting out a rope with weight on the end until it hits the bottom -> Sounding - Depths measured originally in fathoms (length between the outstretched arms of a sailor - > 6 Feet) - Usually shown on rope with knots every 6 feet to indicate a fathom. - Later changed to a single strand of a piano wire, with weight at the end deployed from a winch - Much faster than rope, although still slow - Determining when the weight has hit the bottom (Especially in deep water). Several km's of line can continue to pull more wire from the drum even if the line is on the bottom - Current can cause the line to drift sideways while lowered (or the ship itself can drift), so distance measured is not straight.
Plate Tectonics
- Outermost portion of the Earth is composed of thin, rigid plates that move horizontally with respect to one another.
How can a satellite obtain pictures of the sea floor?
- Sea surface topography can be measured by radar altimetry (Accuracy of 4 cm) - Since rock is denser than water and thus has a higher gravitation attraction, the sea surface is slightly higher over an undersea mountain than a deep area. Reason: The undersea mountain is pulling water towards it, which them piles up over it, raising the sea surface.
Echo sounder limitations
- Tracks not well distributed - Averages over some regions of the bottom - The sound cone from these instruments spreads with depth, and thus can be measuring a large area in deep water. - In idealized case, only the shallowest depth (time of first return) measured. - More realistically, averages over a spectrum of return times - thus does not represent a local extrema in depths. (Look at the provided diagram)
Which features doe Deep ocean basins have?
- Trenches - Guyots - Abyssal Plains - Seamounts
How do we Measuring Bathymetry?
1. Sounding 2. Echo sounder 3. Satellites
How wide is the mid oceanic ridge?
1000 km wide
How much space do mid oceanic ridges take on the face of the earth?
23%
Sonar
A device sending signals into the water and receiving them back.
Passive Margin
A passive margin is the transition between oceanic and continental lithosphere which is not an active plate margin. Rifting
World's Smallest and shallowest ocean?
Arctic Ocean
What is the Second largest ocean?
Atlantic Ocean
Which ocean exists mainly in the southern hemisphere?
Indian Ocean
What is an ocean trench?
Narrow ditch formed at the oceanic ridge.
What is Rift Valley?
Oceanic ridge vs oceanic rise A large elongated depression with steep walls formed by the downward displacement
What is Pillow lavas?
Smooth, rounded lobes of rock lava that has solidified as rounded masses, characteristic of eruption under water.
Ocean defined by Antarctic Convergence and surrounds Antarctica
Southern ocean
What is convergence?
Tectonic plates coming together and colliding.
What is divergence?
Tectonic plates going away from each other.
Continental shelf
The area of seabed around a large landmass where the sea is relatively shallow compared with the open ocean.
Continental Rise
The continental rise is an underwater feature found between the continental slope and the abyssal plain.
What builds the features of the Crust?
The interaction between moving plates.
What is Bathymetry?
The measurement of depth of water in oceans, seas, or lakes.
What is Radar altimetry?
The measurement of height or altitude using a radar.
Continental Slope
The sea floor below the break is the continental slope.
Shelf break
The shelf usually ends at a point of increasing slope (called the shelf break).
Which plate sinks under?
The thinner plate sink under and the more it sinks the more it pull, forcing the rest of the plate to move faster too.
What is a Transform fault?
a strike-slip fault occurring at the boundary between two plates of the earth's crust.
Examine the videos on Pillow Lava & Rift Valleys
https://www.youtube.com/watch?v=hmMlspNoZMs (Volcanic activity) https://www.youtube.com/watch?v=DdIUuUY0L9c (Pillow lava)
Watch provided videos:
https://www.youtube.com/watch?v=zocutif0cQY https://www.youtube.com/watch?v=kwfNGatxUJI
