Lecture 18: Oceans Part 2 Flashcards
-Wave Motion in the Oceans -Tidal Cycles -Global Sea Level Changes Over Geological Time -Ocean Sediments
How do waves occur?
They occur due to the effect of wind acting on the surface of the ocean (friction).
What is the motion of water and in which direction does it decrease?
It follows looping orbitals and decreases downward to the wave base where it becomes negligible.
How does shallow water affect waves?
Wave orbitals begin to flatten because of the friction that occurs when the wave base interacts with the base of the seafloor.
What is the surface zone and how does it affect the sea floor?
It is the zone where the wave crests overtake deeper water, causing the waves to break. It causes stronger erosion.
Where is the wave parallel to?
The seafloor contours and the waves become more parallel as the wave base encounters the seafloor.
What is longshore drift?
When waves approach the shore obliquely and undergo refraction, the oscillating motion of water is converted to a longshore current which causes sediment to be carried along the shore in that direction.
What are tides?
The rise and fall of the level of the ocean at coastlines twice per day.
How do tides form?
They are the result of the gravitational interactions between the Earth with the Moon and Sun (More so with the Moon).
The hydrosphere is pulled into an ellipsoid shape, with high tides both nearest and farthest from the center of mass.
What are spring tides and how are they formed?
They are the seasonal extreme tides: highest high tides and lowest low tides. They occur when the Sun and Moon are both in line with the Earth.
What are neap tides and how are they formed?
The other tidal extreme: lowest high tides and highest low tides. Occur when the Sun and the Moon at 90º from each other with respect to the Earth.
What is are eustatic changes?
Another name for worldwide sea level changes.
How does climate affect eustatic changes?
It affects glaciers, ice sheets, and ice caps by either causing them to melt more resulting in higher sea levels or causing them to freeze more water resulting in lower sea levels.
What is another reason the global sea level has changed?
Tectonic activity. (seafloor spreading, subduction, collisions, etc.)
What are the three primary reasons for local sea level changes?
- Tectonic movement
- Isostatic responses to ice caps and ice sheets
- The compaction of sediments
Where can ocean sediment be deposited?
- Near the coast (beaches)
- On the continental shelf
- In the deep ocean (called pelagic sediment)
What is the benthic zone?
Refers to the bottom of the ocean and organisms that live there.
What is the pelagic zone
Is the water column.
What is the photic zone?
One subdivision of the pelagic zone, where the sunlight reaches (approximately the top 200m).
What is the aphotic zone?
One subdivision of the pelagic zone, below the photic zone.
What is the littoral zone?
One subdivision of the ocean as a function of distance from the shore. Is the thin region near the shore that experiences tides.
What is the neritic zone?
One subdivision of the ocean as a function of distance from the shore. Goes from the position of low tide to the continental shelf.
What is the oceanic zone?
One subdivision of the ocean as a function of distance from the shore. Is beyond the shelf.
How are deltas formed?
Form in areas where a river enters into the sea and th erosional action of waves and currents is not great enough to remove all sediment being transported in the river, causing a sediment pile to build out into the sea.
What are estuaries?
- Semi-enclosed embayments that are fed by freshwater from one or more rivers.
- Areas of rapid changes in water salinity, which creates an environment in which sediment may deposit but also one that hosts a great variety of plant and animal life.
What are beaches?
-Accumulations of well-sorted sediment that lie at the edge of water bodies
What are reefs?
They are structures of calcium carbonate built up from the sea floor if the deposition can keep pace with tectonic subsidence.
What are atolls?
Reefs that form around former volcanic islands.
What are continental shelves?
- Large areas that are part of the continent where the depth below sea level is greater than 200m.
- Covered by either clastic sediment or carbonate sediment (in tropical areas of high productivity)
What is pelagic clay?
It is a pelagic sediment that is derived from continents and islands.
What is pelagic ooze?
It is a pelagic sediment that is the shells of microscopic organisms.
What is a turbidite and how does it occur?
It is a geologic deposit which may reach the deep sea floor and it occurs at the continental slope when gravity causes an underwater avalanche of sediment.
