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THE INSIDE STORY:
TIDES
Robert Perry
Malibu High School
What are TIDES ?
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.
High tide
Low tide
High tide
Low tide
Interval between successive high tides = 12 hours, 25 minutes
Q. How long between high tide and low tide ?
What is the #1 cause
of ocean tides?
(hint)
Spring tides
gravity
gravity
Neap tides
gravity
gravity
Isaac Newton
(1642 -1727)
was the first
person to
explain tides
scientifically.
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.
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.
Moon + tide graphics courtesy of US Navy
http://pao.cnmoc.navy.mil/educate/neptune/trivia/physical.htm
Spring Tide
High tides and low tides
are extreme.
Perigean tides
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.
Woods Hole
Sea Grant
Source: builtstronger.com
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.
(Calendar courtesy of
Tidelines, Inc)
Q. What type of tide do we have here
in southern California ?
(Calendar courtesy of
Tidelines, Inc)
Q. What type of tide do we have here
in southern California ?
A. mixed tide.
How do tides
affect marine life
at the beach ?
High tide
Organisms
covered by water.
Low tide
Organisms
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
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.
THE
END
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prepared for UCLA
OceanGLOBE participants.
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