Oceanography Ch 4
Abyssal plains and hills (Note: most abundant feature on Earth)
Abyssal plains - flat, featureless expanse of ocean floor. Abyssal hills - protrusions off abyssal plain.
Continental margins (know details of both active and passive margins)
submerged portion of continent Passive margin - faces spreading centers Active margin - faces converging or transform boundary
What causes sea levels to change?
Ice caps melting
Submarine Canyon and shelf breaks
Submarine canyon - erosion of continental margin accumulating sediment on ocean floor.
Epicenter
earthquake's origin from focus to surface
How are measurements done now?
(a) Echo sounders sense the contour of the seafloor by beaming sound waves to the bottom and measuring the time required for the sound waves to bounce back to the ship. If the round-trip travel time and wave velocity are known, distance to the bottom can be calculated. The depth is equal to the velocity of sound waves in seawater (V) times one-half the time (T) required for sound to travel from the source to the bottom and back to the receiver. (c) An echo sounder trace. A sound pulse from a ship is reflected off the seabed and returns to the ship. Transit time provides a measure of depth. For example, it takes about 2 seconds for a sound pulse to strike the bottom and return to the ship when the water depth is 1,500 meters (4,900 feet). Bottom contours are revealed as the ship sails a steady course. In this trace, the horizontal axis represents the course of the ship; the vertical axis represents the water depth. The ship has sailed over a small submarine canyon.
Turbidity Currents
underwater avalanche of sediment Usually triggered by earthquakes Can carve canyons far below surface
How have sea levels changed in the past?
As the temperature of the Earth changes, so does sea level. Temperature and sea level are linked for two main reasons: Changes in the volume of water and ice on land (namely glaciers and ice sheets) can increase or decrease the volume of water in the ocean
Which is greater, the average height of the continents or the average depth of the ocean?
Average ocean depth greater than average land elevation. A graph showing the distribution of elevations and depths on Earth. There are two dominant levels on our planet, one exposed and the other submerged. This curve is not a land-to-sea profile of Earth, but rather a plot of the area of Earth's surface above any given elevation or depth below sea level. Note that more than half of Earth's solid surface is at least 3,000 meters (10,000 feet) below sea level. The average depth of the world ocean (3,796 meters, or 12,451 feet) is much greater than the average height of the continents (840 meters, or 2,760 feet).
Continental shelf, slope and rise
Continental shelf - shallow submerged continent extension Continental slope - transition between shelf and ocean floor Continental rise - accumulated sediment from continent Ocean ridges - newly erupting basalt at spreading centers.
Are sea levels going up or down? Why?
Current sea levels are currently much higher than normal due to the polar icecaps melting
Hydrothermal vents (also called black smokers)
Hot springs located near spreading centers. 660°F
Bathymetry
Mapping depths below the ocean's surface
Seamounts and guyots
Seamounts - remnants of active spreading center or hot spots Guyots - similar to seamounts but flat on top
Where are the deepest parts of the ocean found?
The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean in the southern end of the Mariana Trench, which runs several hundred kilometers southwest of the U.S. territorial island of Guam. Challenger Deep is approximately 36,200 feet deep.
Where are they now related to the minimum and maximum height they have been?
The rise and fall of sea level is due largely to the coming and going of ice ages—periods of increased and decreased glaciation, respectively. Because water that formed the ice-age glaciers came from the ocean, sea level dropped. Point a indicates a low stand of 125 meters (410 feet) at the climax of the last ice age some 18,000 years ago. Point b indicates a high stand of 6 meters (19.7 feet) during the last interglacial period about 120,000 years ago. Point c shows the present sea level. Sea level continues to rise as we emerge from the last ice age and enter an accelerating period of global warming.
How were the earliest depth measurements of the ocean bottom taken?
The winch was used to lower a weight on the end of a line to the seabed to find the ocean depth.
Trenches and island arcs
Trenches - arc-shaped depression caused by subduction. Deepest places Island arcs - region of islands found near trenches