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Chapter 15: The Dynamic Ocean
Terms in this set (115)
a surface current in the Atlantic Ocean that flows northward along the East Coast of the United States
How are surface currents similar to the Gulf Stream set in motion?
What happens to energy at the water surface where the atmosphere and the ocean meet?
energy is passed from moving air to the water through friction
What causes the surface layer of water to move in currents?
the drag exerted by the winds blowing steadily across the ocean
Prevailing winds that blow northeast from 30 degrees north latitude to the equator and that blow southeast from 30 degrees south latitude to the equator
Dominant winds of the mid-latitudes. These winds move from the subtropical highs to the subpolar lows from west to east.
What causes large circular-moving loops of water in the Atlantic Ocean?
the trade winds and the westerly winds
Huge circular moving current systems dominate the surfaces of the oceans, large whirls of water with in an ocean basin
What are the five main gyres?
North Pacific, South Pacific, North Atlantic, South Atlantic, Indian Ocean Gyre
Why are these gyres often called the subtropical gyres?
the center of each gyre coincides with the subtropics at about 30 degrees north or south latitude
Causes moving air and water to turn left in the southern hemisphere (counterclockwise) and turn right in the northern hemisphere (clockwise)due to Earth's hemisphere.
Why do the gyres flow in different directions in two hemispheres?
the Coriolis effect
What are all the currents that exist within the North Pacific Gyre?
4: North Equatorial, Kuroshio, North Pacific, and the California Current
How many currents are in the North Atlantic current?
What happens to the North Equatorial current?
beginning near the equator, the current is deflected northward through the Caribbean, where it becomes the Gulf Stream.
What happens to the Gulf Stream as it moves along the East Coast of the United States?
it is strengthened by prevailing westerly winds and is deflected to the east (right) offshore of North Carolina into the North Atlantic
What happens the Gulf Stream as it move northeastward?
it gradually widens and slows until it becomes a vast slow moving current known as the North Atlantic Current, also known as the North Atlantic Drift because of its sluggish nature
What happens as the North Atlantic Current approaches Western Europe?
it splits, part of it moves northward past Great Britain, Norway, and Iceland, carrying heat out to these chilly areas while the other part is deflected southward as the cool Canary Current
What happens as the Canary Current moves southward?
The current merges into the North Equatorial current completing the North Atlantic Current's path
What is the difference in surface ocean currents in the south Atlantic and the South Pacific compared to the Northern Hemisphere?
the direction of flow in the South is counterclockwise
Describe the circulation pattern of the Indian Ocean
the pattern is similar to other southern Hemisphere ocean basins because it exist mostly in the Southern Hemisphere
What is the only current that completely encircles Earth?
West Wind Drift
Why do the cold waters circulate in a loop in the West Wind Drift?
the drift is located near Antarctica where there are no landmasses in its way
What does the West Wind Drift move in response to?
the Southern Hemisphere prevailing westerly winds and portions of it split off into the adjoining southern ocean basins
What doe the gains in energy on Earth equal to?
losses to space of heat radiated from the surface
What happens to the energy gains when considering most latitude individually?
there is a net gain of energy in lower latitudes and a net loss in higher latitudes
currents from low latitude into high latitude (warm currents) transfer heat from warmer to cooler areas
when is the influence of cold currents most pronounced?
in the tropics during the summer months in the middle latitudes
What do cold currents do?
chill the air and increase acidity
the rising of cold water from deeper layers to replace warmer surface water is a common wind-induced vertical movement
Where is coastal upwelling most characteristic?
along the west coasts of continents, most notably along California, Western South America, and West Africa
When does coastal upwelling occur?
when the winds blow toward the equator and parallel to the coast
What causes surface water to move away from the shore?
coastal winds combined with the Coriolis effect
What happens as the surface layer of water moves away from the coast?
the water is replace with other water that upwells from below the surface, this water is cooler and results in lower surface-water temperatures near the shore
What does upwelling bring?
greater concentrations of dissolved nutrients, such as nitrates and phosphates, to the ocean surface promoting the growth of microscopic plankton supporting extensive populations of fish and other marine organisms
What is Deep-Ocean Circulation a response to?
density differences among water masses that cause denser water to sink and slowly spread out beneath the surface
density variations that cause deep ocean circulation caused by differences in temperature and salinity
What can cause an increase in seawater density?
a decrease in temperature or an increase in in salinity
Where do most water involved in deep-ocean currents begin?
in high latitudes at the surface
What happens to salinity in regions where water is involved in deep-ocean currents and the surface water is cold?
salinity increases when sea ice forms
What happens to salinity when seawater freezes to form sea ice?
salts do not become part of the ice and the salinity (density) of the remaining seawater increases
What happens when the surface water that is frozen and forms sea ice becomes to dense?
the surface water sinks initiating deep ocean currents
What happens after the frozen surface water sinks initiating deep ocean currents?
when the water sinks, it is removed from the physical processes that increased its density in the first place and so its temperature and salinity remain largely unchanged for the duration of the time it spends in the deep ocean
the line that marks the contact between land and sea
How do the tides affect the position of the shoreline?
as the tides rise and fall each day, the position of the shoreline migrates
the area that extends between the lowest tide level and highest elevation on land that is affected by storm waves
extends inland from the shore as far as ocean-related features can be found
the coast's seaward edge, where as the inland boundary is not always obvious or easy to determine
What is the shore divided into?
the foreshore and the backshore
the area exposed when the tide is out (low tide) and submerged when the tide is in (high tide)
landward of the high-tide shoreline, usually dry being effected by waves only during storms
between the low-tide shoreline and the line where the waves break at low tide
seaward of the nearshore zone
an accumulation of sediment found along the landward margin of an ocean or a lake
relatively flat platforms often composed of sand that are adjacent to coastal dunes or cliffs and marked by a change in slope at the seaward edge
the wet sloping surface that extends from the berm to the shoreline
What are beaches composed of?
whatever material is locally abundant
Where is the sediment from some beaches derived from?
erosion of adjacent cliffs or nearby coastal mountains, others are built from sediment delivered to the coast by the rivers
Why are beaches thought of as material in transit along the shore?
because beaches do not stay in one place due to the waves crashing into the material the beaches are made of that are constantly being moved
energy traveling along the interface between ocean and atmosphere often transferring energy from a storm far out at sea over distances of several thousand kilometers
What type of wave produces the most energy that shapes and modifies the shorelines?
What does a shoreline do to a wave?
the shoreline breaks up the wave causing it not to move
Where do waves derive their energy and motion from?
crest and trough
the highest point of a wave
the lowest point of a wave
What are the measurements of a wave?
wave height, wave-length, and wave period
the vertical distance between trough and crest
the horizontal distance between successive crest or successive troughs
the time it takes for one full wave, one wavelength, to pass a fixed position
What are the three factors of the height, length, and period that are eventually achieved by a wave?
wind speed, length of the wind that has blown, and fetch
the distance that wind has traveled across open water
What happens to a wave as the quantity of energy transferred to the water increases?
the height and the steepness of the waves increase
the point at which waves grow so tall that they topple ove r
What does it mean when the waves are fully developed?
a particular wind speed has a particular maximum fetch and duration of wind beyond which waves will no longer increase in size, When the maximum fetch and wind duration are met, the wave can no longer build height because they are losing as much energy through the breaking of whitecaps as they are receiving energy from the wind
What happens to the waves when the wind stops, changes direction, or they leave the storm where they were created?
the waves continue on without relation to the local winds.
lower in height and longer in length and may carry a storm's energy to distant shores
What is the motion that waves move through when energy passes in the water?
they move in a circular orbital motion
The depth below the surface where the circular orbits become so small that movement is negligible. It is equal to one-half the wavelength
Why does a wave break when it reaches the shore?
a crucial point in the wave is reached where the wave is too steep to support itself and wave front collapses or
What slows the advance of a wave
the ocean depth, if it is too shallow it will slow
turbulent water created by breaking waves
on the landward margin of the surf zone, the turbulent sheet of water from collapsing breakers
the sawing and grinding action of the water armed with rock fragments
Why is each breaking wave dangerous
the waves hurls tons of water against the land, sometimes causing the ground to tremble
Where is abrasion thought to possibly be more intense?
in the surf zone
Why are beaches sometimes called rivers of sand?
the energy from breaking waves often causes large quantities of sand to move along the beach face and in the surf zone roughly parallel to the shoreline, wave energy also causes sand to move perpendicular (toward and away from) to the shoreline
the bending of waves
What does wave refraction do to the shoreline processes?
it affects the distribution of energy along the shore and thus strongly influences where and to what degree erosion, sediment transport, and deposition will take place.
In what direction do waves approach the shoreline?
at an angle
What happens when a wave reaches the shallow water of a smoothly sloping bottom?
they are bent and tend to become parallel to the shore
Why does the parallel bending of a wave at a shallow smoothly sloping bottom occur?
the part of the wave nearest to the shore reaches shallow water and slows first, whereas the end that is still in deep water continues forward at its full speed
How does an irregular shoreline get straightened over time?
the waves are bent as they reach the shallow water in front of the headland sooner than they don in adjacent bays bending nearly parallel to the protruding land and strike it from all three sides, the refraction in bays cause the waves to diverge and expend less energy, in zones of weakened wave activity, sediment can accumulate and form sandy beaches. over time the erosion of headlands and deposition in the bays are no longer protruding
Movement of sediment by the longshore current
the transport of sediment in a zigzag pattern along a beach caused by the uprush of water from obliquely breaking waves
ocean currents that run parallel to the shore
Why has the beach often been characterized as a river of sand?
bothe rivers and coastal zones move water and sediment from one area (upstream) to another (downstream)
features that originate primarily because of erosional features
accumulations of sediments
What is the shoreline erosion influenced by?
the proximity of coasts to a sediment-laden river, the degree of tectonic activity, the topography and the composition of the land, prevailing winds and weather patterns, the configuration of the coastline and nearshore areas
cutting action of the surf against the base of coastal land
a relatively flat benchlike surface
What happens as erosion progresses near a wave-cut cliff?
rocks overhanging the notch at a base of the cliff crumble into the surf and the cliff retreats
When does a wave-cut platform broaden?
as a wave attack continues
When does a wave-cut platform become a marine terrace?
a wave-cut platform gets uplifted above sea level by tectonic forces
What are marine terraces recognized for and desired for?
recognized for: by their gentle seaward-sloping shape, desired for: coastal roads, buildings, or agriculture
an arch formed by wave erosion when caves on opposite sides of a headland unite
How does a sea arch form?
when waves erode a layer of softer rock that underlies a layer of harder rock
An isolated mass of rock standing just offshore, produced by wave erosion of a headland.
What are depositional features of a beach?
spits, bars, and tombolos
an elongated ridge of sand that projects from the land into the mouth of an adjacent bay
a sandbar that completely crosses a bay, sealing it off from the open ocean
Where does a baymouth bar tend to occur?
across bays where currents are weak, allowing a spit to extend to the other side
a ridge of sand that connects an island to the mainland or to another island, forming in the same manner as a spit
low, narrow, sandy islands that form offshore from a coastline.
What are examples of barrier islands?
The Atlantic and Gulf Coastal Plains, relatively flat and slope gently seaward
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