MOTION IN THE
OCEAN
Waves and Tides
Waves

A disturbance which
moves through or
over the surface of a
fluid
Mostly caused by:
Winds
Earthquakes
Gravitational Pull
Volcanos
 Form of great energy

 When
a wave
passes through the
ocean, individual
water molecules
move up and down
but they do not
move forward or
backward.
http://www.military.com/video/logistics-andsupplies/naval-equipment/warship-takeson-massive-waves/1910420040001/
 http://oceanexplore
r.noaa.gov/edu/lear
ning/player/lesson0
9.html
Wave Characteristics

Parts of a Wave

Crest = high point

Trough = low point


Height = vertical
distance from crest to
trough
Wavelength =
Horizontal distance
between crest to crest
or trough to trough
Size of Wind Generated
Waves

Depends on 3 things:



Wind Speed
Wind Duration (length of
time wind blows)
“Fetch” Extent of open
water across which the
wind can blow
Water Motion in Waves

Water travels in vertical
circular orbits

Wave moves, particles don’t!
Importance of Waves
 Shaping
Coastlines


Erode cliffs
Grind rock into sand
 Ecology


Returns O2 to water
Stir up food for filter
feeders
Types of Waves
CHOP – Short period (back bays)
SWELL – Long period (boat rolls; seasickness)
SWASH – water up beach
BACKWASH – back down
TSUNAMI
“TIDAL WAVE”
Caused by undersea quake or volcano
• Wavelength = ~150 mi.
Can NOT perceive in boat
Wave height = 6” – 1’
Speed > 500 mph
Slows down to ~25 mph at shore; water builds up to ~65+ ft
Tsunami Waves
Creation of a Tsunami
Before the 2004 Indian Ocean tsunami The man on the left is about to
reached Sri Lanka, many animals, like
be killed by the tsunami that struck
this elephant, moved to high ground
Hilo, Hawaii in 1946.
and survived
Hundreds of thousands of
people died in the December
26, 2004 Indian Ocean
tsunami. But as described in
these news reports, others
saw warning signs, and
escaped with their lives.
Thousands died on the beaches of Thailand in the December 2004 tsunami. But a 10-year-old British girl saved more than 100
people because she had just studied the killer waves in school. When the sea suddenly began to boil, then pulled away from the
resort she was visiting, leaving fish and boats stranded high and dry, Tilly Smith recognized that a tsunami was approaching.
Fortunately, her frantic warnings were heeded, and the beach was evacuated just moments before the huge waves crashed
ashore.
Kalutara Beach Detail
Imagery collected December 26, 2004. Description: Receding waters and beach damage from tsunami
"Primitive" Tribe Survives Tsunami
Off the coast of India, the remote Andaman
Islands are home to the aboriginal Onge
(pronounced OHN-ghee) a tribe that follows
an ancient hunter-gatherer lifestyle. On
December 26, 2004, when the creek that
ran through their settlement suddenly went
dry and the sea pulled away from the shore,
the Onge took immediate action. Believing
that evil spirits were at work, the tribe
scattered pig and turtle skulls around their
settlement and threw stones into the sea,
then quickly gathered their possessions and
ran inland.
Moments later, a tsunami slammed into the
island of Andaman. All 96 Onge survived
the tsunami because of their awareness of
natural processes. Many other people in the
region were less attuned to nature, and paid
with their lives. When the seabed was
exposed by the approaching tsunami,
tourists visiting the coast of Thailand
wandered curiously toward the receding
ocean, and Indonesian fisherman ran to
pick up fish left high and dry, oblivious to the
danger.
TABLE TALK




Apparently, some animals are alerted to the approach of
a large tsunami in ways that humans can't detect.
Speculate about what warning signs animals might pick
up that people cannot.
Describe several warning signs that often precede
tsunami.
Why do you think so many people ignore these
indicators?
If you detect any tsunami warning signs, what should
you do?
 http://www.onr.navy.mil/focus/ocean/motio
n/waves1.htm
Early thoughts about what
caused the tides.
 Some
believed the earth was a living
animal and the tides a result of its
breathing.
 Others, who thought the ocean’s waters
were the earth’s blood, decided the
tides were its pulse, caused by the
beating of its great heart.
Early thoughts about what
caused the tides.

Early followers of the religious prophet
Muhammad believed that the rise and fall of
the waters were caused when the “Angel of
the Sea” placed his foot in and out of the
ocean.
 Primitive natives thought the tides were a
sign of a sea god’s anger and made human
sacrifices to please him.
Sir Isaac Newton to the Rescue!
 Newton’s
Universal
Gravitation theory
helped to explain
how the gravity of
the moon (and the
sun) were related
to tides.
Tides

The rhythmic rise and
fall of the ocean’s water
High tide = rising, incoming
tide, flow
Low tide = receding, outgoing
tide, ebb
Slack tide = vertical movement
stops
http://oceanexplorer.noaa.gov/edu/learning
/player/lesson10.html
What Causes Tides?
1. Gravitational pull of
sun & moon on Earth
• Moon closer, therefore
> effect
• Like magnet, pulls water
away from surface
= TIDAL BULGE
http://oceanservice.noaa.gov/education/kits
/tides/media/supp_tide04.html
Tides are generated by:
• the gravitational pull of the moon and sun
- moon has 2x greater gravitational pull than the
sun
- sun is 10 million x more massive than the
moon and is 390 times farther away

Tides are very long,
slow waves



They have a wave
period of 12 hours 25
min
Tidal day is 24 hours
50 min
NJ has 2 high and 2
low tides daily
2. Centrifugal Forces
• Produced by motions of
Earth, sun, & moon
• Bulge on opposite side
because centr. force
> pull of moon
Centripetal force
Types of Tides
•Spring Tide
- Moon and sun are in direct
line with one another
- Results in unusually
high tidal range
-Tidal Range = vertical
distance between high &
low tides

2x’s/month

Neap Tide




sun and moon are at
right angles
Pulls cancel each
other out – causes a
weak pull
unusually low tidal
range
2 x’s / month
Spring vs. Neap Tides
http://oceanservice.noaa.gov/education/kits
/tides/media/supp_tide06a.html
The monthly tidal cycle
(29½ days)
About every 7 days, Earth alternates
between:

Spring tide
• Alignment of Earth-Moon-Sun system (syzygy)
• Lunar and solar bulges constructively interfere
• Large tidal range

Neap tide
• Earth-Moon-Sun system at right angles
(quadrature)
• Lunar and solar bulges destructively interfere
• Small tidal range
Distance bet. Moon & Earth
Perigee Tides
• Moon closest to earth, very high tides (causes
flooding)
Apogee Tides
• Moon farthest away from earth, very low tides
Types of Tides Continued

Diurnal Tides

1 high & 1 low / day

Parts of Gulf of Mexico
and Asia

Semi-Diurnal Tides

2 high & 2 low / day

Atlantic coasts of North
America and Europe

Mixed

2 high & 2 low / day
(height varies)

Pacific coast
http://oceanservice.noaa.gov/education/tut
orial_tides/media/supp_tide01.html
Importance of Tides
• Expose & submerge orgs
• Circulate water in bays &
estuaries
• Circulates food, wastes, etc
• Trigger spawning (grunion,
horseshoe crab)
Impacts of Tides
Predicting tides has always been
important to people who look to
the sea for their livelihood.
Commercial and recreational
fishermen use their knowledge of
the tides and tidal currents to help
them improve their catches.
Depending on the species and
water depth in a particular area,
fish may concentrate during ebb or
flood tidal currents. In some areas,
strong tidal currents concentrate
bait and smaller fish, attracting
larger fish. In addition, knowledge
of the tides has also been of
interest to recreational beachgoers
and surfers.
Currents
• What are currents?
- “Rivers” of circulating water
• Causes
- Wind
- Rotating Earth
- Density Changes
Ocean Circulation

Currents are also a product of the wind.
 Current can be in surface layers of deeper water
layers
 Both winds and the currents they drive are
affected by the Coriolis Effect.
 Because the earth spins continuously, anything
that passes over the earth is deflected.
Ocean Circulation

In the northern hemisphere, winds and currents
are deflected to the right.
 In the southern hemisphere, winds and currents
are deflected to the left.
 This deflection termed the Coriolis Effect. Since
the Earth is spinning, it causes this defection of
winds and currents.
 This deflection often causes currents to travel in
circular patterns called gyres.
•
Coriolis Effect
- N. Hemis – clockwise; Right
- S. Hemis – counterclockwise; Left
Coriolis Effect
https://www.youtube.com/watch?v=i2mec3
vgeaI
https://www.youtube.com/watch?v=Pb69H
ENUZs8
http://video.mit.edu/watch/the-corioliseffect-4407/
Ocean Circulation

Despite repeated mixing by winds and currents
at the ocean’s surface, the ocean is still stratified
into three layers:
–
–
–
Surface layer – from surface to about 200 meters; this
layer stays well mixed most of the year.
Intermediate layer - from 200 – 1500 meters; major
temperature change (thermocline) is located here.
Less mixing occurs here.
Bottom layer – below 1500 meters; low mixing and
normally uniformly cold.
Deep Ocean Currents
DRIVE THE OCEAN CONVEYOR BELT
Flow
beneath surface; cross
equator
Move North to South

Separated from surface
currents by boundary
called a “Thermohaline”
In some locations, large volumes of water
may sink or rise.
Water sinks due to changes in temperature
and salinity – this is known as an area of
down-welling.
Down-welling brings gases from the
surface to deeper layers.
Importance Of Deep Currents

Upwelling
• Brings deep water to surf.
• Circulates nutrients up
• Moves plankton & larvae
Surface Ocean Currents
• Broad, slow drifts; never
cross equator
• Wind generated; circular
gyres
• Gulf Stream
- N. Atlantic
- Brings warm water
from equator north along
east coast of N. A.
-Sometimes form eddies –
circulating water that
pinches off from the
current
NAVIGATION
MIGRATION
WEATHER
Localized Surface Currents
Longshore Current.

Flows parallel to shore; move sediment
RIP CURRENT
- Caused by converging longshore currents
- Very dangerous ; Red Flag
- DO NOT fight rip current; swim parallel to shore to
get out of channel
http://www.deepseanews.com/2012/06/mu
st-watch-video-on-rip-currents/
http://www.hamilton.k12.nj.us/webpages/as
chwing/resources.cfm?subpage=358703