D EE SS TT II D ROBERT PERRY Malibu High School OceanGLOBE
UCLA
What are TIDES ? Tides are the regular and predictable variations in sea level
Click on this link to view the above animation: http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide01.html
High tide
Low tide
High tide
Low tide
Interval between successive high tides = 12 hours, 25 minutes Interval between moonrises = 24 hours, 50 minutes THINK, COMPUTE, AND ANSWER THIS Q: Q. How long between high tide and low tide ?
What causes ocean tides? HINT: YOU ARE HERE--->
TIDES ARE CAUSED BY GRAVITY “PULLING” ON THE EARTH: 1-GRAVITY OF SUN (SMALL EFFECT)
SUN HAS MORE MASS AND MORE GRAVITY, BUT IS MUCH FARTHER AWAY FROM EARTH
+ 2-GRAVITY OF MOON (BIG EFFECT)
MOON HAS LESS MASS AND LESS GRAVITY, BUT IS MUCH CLOSER TO EARTH
Greatest tidal range: Spring tides
gravity
gravity
Least tidal range: Neap tides
gravity gravity http://astrosun.tn.cornell.edu/courses/astro201/moon.htm
Water tends to accumulate on the parts of the Earth's surface directed toward and directly opposite the Moon & Sun due to the rotation of the Earth!
4 PHASES OF MOON AND ITS EFFECT ON THE TIDES
Earth
Pronounce syzygy: http://www.youtube.com/watch? v=bhyWrPy7f-w&noredirect=1
Neap Tide High tides and low tides are not extreme.
NEAP TIDES. High tides and low tides are of minimal range.
SPRING TIDES. High tides and low tides are extreme. (Calendar courtesy of Tidelines, Inc)
Spring Tide
High tides and low tides are extreme.
Syzygy ! Moon + tide graphicscourtesy of US Navy http://pao.cnmoc.navy.mil/educate/neptune/trivia/physical.htm
Spring Tide
High tides and low tides are extreme.
Syzygy !
APOGEE
PERIGEE
The point FARTHEST the earth's center in the orbit of the moon or sun. The point NEAREST the earth's center in the orbit of the moon or sun.
KING TIDES !
KING TIDES (SPECIAL PERIGEAN TIDES) A perigean, or KING tide refers to a tide that occurs when the moon AND the sun are closest to the earth. The moon's orbit around the earth is elliptical rather than circular, which means that the distance between earth and moon is always changing. Perigee refers to the time when the moon or sun and the earth are closest to one another. At perigee, the moon is about 30,000 miles closer to earth than at apogee, when the moon is farthest from earth. Perigee is reached about once a month, roughly the time it takes for the moon to revolve around the earth. When the moon is closest to earth, its effect on tides is greatest.
How might tides combine with storm surf to cause property damage ?
tide
Adapted from Woods Hole Sea Grant
Types of tides
SEMIDIURNAL
MIXED
DIURNAL
Semi-diurnal tides have two high and two low waters per tidal day. They are common on the Atlantic coasts of the United States and Europe.
Mixed tides have a higher high water and lower high water as well as higher low water and lower low water. The tides around west coast of Canada and the United Sates are of this type.
In parts of the northern Gulf of Mexico and Southeast Asia, tides have one high and one low water per tidal period.
SOUTHERN CALIFORNIA TIDES
(Calendar courtesy of Tidelines, Inc)
Q. What type of tide do we have here in southern California ?
SOUTHERN CALIFORNIA TIDES
(Calendar courtesy of Tidelines, Inc)
Q. What type of tide do we have here in southern California ? A. Mixed semi-durnal tide.
How do tides affect marine life at the beach ?
High tide Marine life on beach covered by water.
Low tide Marine life on beach exposed to air.
Exposure to air causes bands or zones of life along the beach. Intertidal Zone
Total Exposure to Air Hours per Year
Zone 1
High Intertidal
7,200 - 8,760
Zone 2
Upper-Middle
3,200 - 7,200
Zone 3
Lower-Middle
400 - 3,200
Zone 4
Low Intertidal
0 - 400
The grouping or banding of life between the tidemarks (between HHW and LLW) is known as INTERTIDAL ZONATION. Data modified from Hedgepeth, Ricketts and Calvin (1968).
Intertidal Zonation The clusters or bands formed by communities of organisms living within certain tide ranges along the shore. Southern California rocky shore dominant species: Number: 1
Name: Spash
Species: snails
2
Upper-mid
barnacles
3
Low-middle
mussels
4
Low
algae
snails barnacles mussels
algae
Intertidal zones at La Jolla, California
Stephenson & Stephenson (1972)
Intertidal zonation patterns on a rock breakwall in North Carolina.
Stephenson & Stephenson (1972)
Zonation on the west coast of South Africa Stephenson & Stephenson (1972)
Intertidal zonation patterns along the Florida Keys.
Stephenson & Stephenson (1972)
CONCLUSION: Alternate exposure to air and water caused by the tides results in intertidal organisms occupying specific zones according to their range of tolerance to dryness, temperature, predation, feeding, respiration and reproduction. This pattern can be observed world wide.
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