THE INSIDE STORY:

T I D E S

THE INSIDE STORY:

T I D E S

Robert PerryMalibu 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)

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.

Neap TideNeap TideHigh 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 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.

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

How might tides combine with storm surf to cause property damage ?

Source: builtstronger.com

Adapted fromWoods HoleSea 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 herein southern California ?

(Calendar courtesy ofTidelines, Inc)

Q. What type of tide do we have herein southern California ?

A. mixed tide.

(Calendar courtesy ofTidelines, Inc)

How do tidesaffect marine life

at the beach ?

High tide

Low tide

Organismscovered by water.

Organismsexposed to air.

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

Intertidal zonationpatterns on a rockbreakwall in North

Carolina.

Stephenson & Stephenson (1972)

Zonationon the west coast

of South Africa

Stephenson & Stephenson (1972)

Intertidal zonationpatterns along the

Florida Keys.

Stephenson & Stephenson (1972)

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.

T H E E N D

This slide presentation wasprepared for UCLA

OceanGLOBE participants.

Images and materials maybe used outside of theUCLA OceanGLOBE

program for non-profit,educational purposes only.

Send comments to:zalophus@gte.net