Ch 21-Movements of Ocean
• Objectives
– Describe how wind patterns, rotation of Earth and continental
barriers affect surface currents in the ocean
– Major factor that determines the direction in which a surface
current circulates
– Explain how differences in density of ocean water affect the flow
of deep currents
– Describe the formation of waves and the factors that affect wave
size
– Explain how waves interact w/ coastline
– Identify the cause of destructive ocean waves
– Describe the gravitational pull of the moon causes tides
– Compare spring tides and neap tides
– Describe how tidal oscillations affect tidal patterns
– Explain how the coastline affects the tidal currents
Factors that Affect Surface
Currents
• Currents-horizontal movement of water in well
defined pattern
• Surface currents-currents that move on or near
the surface of ocean and are driven by winds
– Controlled by air currents, Earth’s rotation, location of
continents
• What causes winds?
– Uneven heating of the atmosphere
– Air moves from high to low pressure
– Colder, denser air sinks
Global Wind Belts
• Trade winds-located just N and S of
equator, push currents westward
• Westerlies-push ocean currents eastward
in higher latitudes of N and S
Hemispheres
• Both affect flow of ocean surface currents
Rotation and Continental Barriers
• Continental barriers-current is deflected
and divided when surface currents flow
against continent
• Coriolis Effect-apparent curving of the path
of moving object from an otherwise
straight path due to Earth’s rotation
• Gyres-huge circle of moving ocean water
found above and below the equator
Major Surface Currents
• Equatorial Currents-Atlantic, Pacific, Indian. 2
warm water equatorial currents moving west
• Currents in S Hemisphere-Antarctic Circumpolar
Current is largest, no continent interruption
• Currents in N Atlantic-Gulf Stream moves along
E coast of N America. Joins w/ Labrador
current=N Atlantic current joins N Equatorial
Current
• Currents in N Pacific-similar to N Atlantic.
Kuroshio current, flows northward along E coast
of Asia, flows toward N America and cools drift
of California
Deep Currents
• Stream-like movement of ocean water far below the
surface, slower than surface currents, form in polar
regions as cold dense water sinks and flows beneath
warmer ocean water
• Antarctic Bottom Water-dense, cold water sinks to bt,
forms deep current. Moves slowly northward to latitude
of 40 deg N
• N Atlantic Deep Water-begins S of Greenland, flows
southward under Gulf Stream, divides near equator. One
flows northward, other flows southward over the
Antarctic Bt Water
• Turbidity Currents-strong current caused by under water
landslide. What causes it do you think?
Sec 2-Ocean Waves
• Wave-periodic disturbance in a solid, liquid, or gas as
energy is transmitted through the medium
• Crest-highest pt of wave
• Trough-lowest point between 2 crests
• Wave height-vertical distance between the crest and the
trough of a wave
• Wavelength-horizontal distance between 2 consecutive
crests or between 2 consecutive troughs
• Wave period-time required for 2 consecutive wave crests
to pass a given pt
• Wave speed- wavelength/wave period
Wave Size
• What factors determine the size of wave?
– Speed of wind, length of time the wind blows, and
fetch
– Fetch-distance that the wind can blow across open
water
– Swells-long, rolling waves which are similar in size,
move in groups, one waves follows another
– Steady high winds=waves equal great sizes
– Strong and gusty=choppy water w/ waves of great
heights and lengths
• Whitecaps-winds blow the crest of a wave off,
allows less radiation to reach the ocean
Waves and Coastline
• Shallow water near coastline, wave touches the ocean
floor, waves slow and eventually break
• Breakers-top of wave continues at same speed while bt
wave slows as it comes in contact w/ bt.
• Refraction-ocean waves bend directly toward the
coastline in shallow water, shallow water wave travels
slower than wave still in deep water
• Undertows-irregular current, seldom strong
• Rip current-large breakers returning to ocean through
channels, cut through underwater sandbars parallel to
beach
• Longshore Currents-waves that approach beach at an
angle
Tsunamis
• Most destructive wave in oceans
• Not powered by wind
• Giant seismic ocean waves, caused by
earthquakes on ocean floor, volcanic
eruptions and under water landslides
• Height may be 30-40 m
Sec 3-Tides
• http://player.discoveryeducation.com/index.cfm?gu
idAssetId=58229B2B-B806-415F-A8D5D174BB082381&blnFromSearch=1&productcode=
US
• Tides-periodic rise and fall of water level in the
ocean and other large bodies of water
• How does the gravitational pull of the moon cause
tides?
– Gravitational pull of moon is strongest on side of
Earth nearest to moon. Ocean on Earth’s near side
bulges slightly, causes high tide w/in area of bulge.
Causes tidal bulge on opposite side of Earth
Spring and Neap Tides
• Tidal range-difference in levels of ocean water at
high tide and low tide
• Spring tides-Earth, sun, moon are aligned during
new and full moon. Gravitational pull results in
higher high tides and lower low tides
• Neap tides-1st and 3rd quarter phase of moon the
sun and moon are at right angles of each other,
work against each other, daily tidal range is
small
Location and Tidal Range
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Baltimore, MD 1 foot, 8 inches
Charleston, SC 5 feet, 10 inches
Eastport, ME 19 feet, 4 inches
Galveston, TX 1 foot, 5 inches
Key West, FL 1 foot, 10 inches
New London,CT 3 feet, 1 inch
New York, NY 5 feet, 1 inch
Portland, ME 9 feet, 11 inches
San Diego, CA 5 feet, 9 inches
San Francisco, CA 5 feet, 10 inches
Vancouver, B.C 10 feet, 6 inches
Boston, MA 10 feet, 4 inches
Ft. Pulaski, GA 7 feet, 6 inches
Philadelphia, PA 6 feet, 9 inches
St. Petersburg, FL 2 feet, 3 inches
Sandy Hook, NJ 5 feet, 2 inches
Seattle, WA 11 feet, 4 inches
Washington, DC 3 feet, 2 inches.
Tidal Variations
• What affects tidal patterns?
– Size, shape, depth, and location of ocean
basin
• Tidal oscillations-slow, rocking motion of
ocean water that occurs as tidal bulges
move around ocean basins
• Welcome to Discovery Education Player
Tidal Currents
• Movement of water toward and away from the coast,
result of rise and fall of tides
• Flood tide-when tidal currents flow toward the coast
• Ebb tide-tidal current flow toward ocean
• Slack water-no tidal current
• Tidal currents strongest between 2 adjacent coastal
regions
• Tidal bore-river enters the ocean through long bay,
tide may enter the river mouth, surge of water
rushes upstream
• http://player.discoveryeducation.com/index.cfm?guid
AssetId=DDAA2EE0-553B-4C97-82794CBB03CB1FBC&blnFromSearch=1&productcode=
US