THE INSIDE STORY: T I D E S THE INSIDE STORY: T I D E S Robert Perry Malibu High School

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

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 Neap tides gravity Water tends to accumulate on the parts of the Earth's surface directed toward and directly opposite the Moon. Isaac Newton Isaac Newton ( ) was the first person to explain tides scientifically.

Neap Tide High tides and low tides are not extreme.

SPRING TIDES. High tides and low tides are extreme. NEAP TIDES. High tides and low tides are of minimal range. (Calendar courtesy of Tidelines, Inc)

Moon + tide graphics courtesy of US Navy Spring Tide High tides and low tides are extreme.

Spring Tide High tides and low tides are 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 Hole Sea Grant

How might tides combine with storm surf to cause property damage ? Source: builtstronger.com

Adapted from Woods Hole Sea Grant tide

Types of tides

SEMI- DIURNAL MIXED DIURNAL

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 here in southern California ? (Calendar courtesy of Tidelines, Inc)

Q. What type of tide do we have here in southern California ? A. mixed tide. (Calendar courtesy of Tidelines, Inc)

How do tides affect marine life at the beach ?

High tide Low tide Organisms covered by water. Organisms exposed to air.

IntertidalTotal Exposure to Air Zone Hours per Year Zone 1High Intertidal7, ,760 Zone 2Upper-Middle3, ,200 Zone 3Lower-Middle ,200 Zone 4Low Intertidal Exposure to air causes bands or zones of life along the beach. 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:Name:Species: 1Spashsnails 2Upper-midbarnacles 3Low-middlemussels 4Lowalgae

Intertidal zones at La Jolla, California Stephenson & Stephenson (1972) snails barnacles mussels algae

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.

T H E E N D

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