the inside story: t i d e s the inside story: t i d e s robert perry malibu high school
TRANSCRIPT
Tides are the regular and predictable periodic variations in sea level on the Earth that correspond to
changes in the relative positions of the Moon and the Sun.
What are TIDES ?
High tide Low tide
Interval between successive high tides = 12 hours, 25 minutes
Q. How long between high tide and low tide ?
http://astrosun.tn.cornell.edu/courses/astro201/moon.htm
Spring tides
Neap tides
gravitygravity
gravity
gravity
Water tends to accumulate on the parts of the Earth's surface directed toward and directly opposite the Moon.
Isaac Newton (1642 -1727) was the first person to explain tides scientifically.
SPRING TIDES.High tides and low tides are extreme.
NEAP TIDES.High tides and low tides are of minimal range.
(Calendar courtesy ofTidelines, Inc)
Moon + tide graphics courtesy of US Navyhttp://pao.cnmoc.navy.mil/educate/neptune/trivia/physical.htm
Spring TideSpring Tide High tides and low tidesare extreme.
A perigean tide refers to a tide that occurs when the moon is 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 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.
Perigean tides
Woods HoleSea Grant
In parts of the northern Gulf of Mexico and Southeast Asia, tides
have one high and one low water per tidal period.
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.
Q. What type of tide do we have herein southern California ?
A. mixed tide.
(Calendar courtesy ofTidelines, Inc)
Intertidal Total Exposure to Air Zone 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
Exposure to air causes bands orzones of life along the beach.
Data modified from Hedgepeth, Ricketts and Calvin (1968).
Intertidal Zonation
The clusters or bands formed by communities of organismsliving within certain tide ranges along the shore.
Southern California rocky shore dominant species:
Number: Name: Species: 1 Spash snails
2 Upper-mid barnacles
3 Low-middle mussels
4 Low algae
Intertidal zonesat La Jolla, California
Stephenson & Stephenson (1972)
snails
barnacles
mussels
algae
CONCLUSION:
Alternate exposure to air and watercaused by the tides
results in intertidal organisms occupyingspecific zones according to their rangeof tolerance to dryness, temperature,predation, feeding, respiration andreproduction. This pattern can be
observed world wide.
This slide presentation wasprepared for UCLA
OceanGLOBE participants.
Images and materials maybe used outside of theUCLA OceanGLOBE
program for non-profit,educational purposes only.
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