Part 5: Motion of the Ocean
1
Three Types of Motion
1. Waves
2. Currents
3. Tides
2
Waves
 Pulses of energy that
move through water
 Set in motion by:
 Wind (most commonly)
 Earthquakes
 The gravitational pull of
the moon
3
Waves
View the following lesson on waves:
http://oceanexplorer.noaa.gov/edu/learning/player/l
esson09.html
Photo credit: NOAA
4
Waves Caused by Wind
 Called surface waves
 Wind transfers energy to
the water as it moves over
the ocean surface
 The energy then moves
through the water as a
wave
 The water moves up and
down in a circular motion
but does not move
horizontally along the
surface.
 Height of these waves
depends upon:
 Wind speed
 Length of time the wind
blows
 Distance the wind blows
over the water
Animation from http://www.onr.navy.mil/focus/ocean/motion/waves1.htm
5
Characteristics of Waves
 Crest – highest point
 Trough – lowest point
 Wavelength – horizontal
distance between waves
 Wave height – vertical
distance between crest and
trough (amplitude)
 Wave period – time it take
for one wavelength to pass
a give point
 Wave frequency – number
of waves per unit of time
Diagram from: http://www.onr.navy.mil/focus/ocean/motion/waves1.htm
6
Wave Action
 Swells – long, wide waves
 Surf: the surging of the
in the open ocean that
are not very high
 Near the shore,
wavelength decreases,
wave height increases
and crests become more
peaked
 The slope of the shore
determines how the
waves break
ocean waves on to the
shore
 Undertow: water flowing
back to the ocean
View animation:
http://oceanexplorer.noaa.gov/edu/
learning/player/lesson09/l9la1_a.ht
ml
7
Tsunamis
 Caused by sudden
displacements in the sea
floor (earthquakes),
landslides, or volcanic
activity
 Resulting waves can be
very tall (up to 35 m
when they strike)
 Can cause great damage
and loss of life along the
coast
Animation from:
http://www.tsunami.noaa.gov/tsunami_story.html
The 12/26/2004 tsunami in the Indian Ocean killed over 230,000 people.
8
Currents
 Movement of ocean water in streams or
rivers
 Can flow for great distances
 Can play a dominant role in determining the
climate of a region
 Caused by two factors:
 Wind patterns
 Differences in water density
9
Surface Currents
 Caused mainly by wind
patterns
 To depths of ~400 m
 Video:
http://svs.gsfc.nasa.gov/
vis/a000000/a003800/a0
03827/prepetual_ocean_1
080p30.mp4
 Circular motion
 Clockwise in the
Northern Hemisphere
 Counterclockwise in the
Southern Hemisphere
(as with winds)
 May be warm or cold,
depending on where
they originate
10
Long Distance Surface Currents
Generally west coasts have cold currents & east coasts have warm currents
11
Long Distance Surface Currents
Gulf Stream
 About 150 km wide, up to
1,000 m deep, speed
averages 6.4 km/h (4 mph)
 Carries warm water from
the southern tip of Florida
north along the east coast
of the US
 Video
http://www.teachersdomai
n.org/resource/ess05.sci.es
s.watcyc.drifters/
 Interactive diagram of 25
major ocean currents
http://www.srh.noaa.gov
/jetstream/ocean/curren
ts_max.htm
12
Short Distance Surface Currents
 Found near shorelines
where waves hit at an
angle
 Longshore currents
move parallel to the
shoreline
 Pick up sand and other
materials and then
deposit them in the
water close to the
shoreline forming a
sandbar
Sandbar off Long Island Coast
Photo credit: David Shankbone, August 2006.
13
Short Distance Surface Currents
 If the current cuts
through a sandbar, the
resulting powerful,
narrow, outflow back to
the ocean is a rip current.
 A rip current is a type of
undertow.
 As the sandbar is often
underwater, rip currents
are difficult to see and
dangerous.
14
Deep Currents
 Caused by difference in
density of water
 Density affected by:
 Temperature
 Salinity
 Colder, saltier water at
the poles sinks to the
depths of the ocean and
then moves away from
the poles.
 Most flow in directions
opposite that of surface
currents
Global Ocean Conveyor Belt. This collection of
currents is responsible for the large-scale
exchange of water masses in the ocean,
including providing oxygen to the deep ocean.
The entire circulation pattern takes ~2000 years.
15
Upwelling
 The rising of deep cold
currents to the ocean
surface
 Occurs when winds blow
parallel to the coastline
 Carries nutrient rich
waters to the surface to
support high levels of
seaweed and plankton
growth.
 These areas are the best
fisheries.
Areas of coastal upwelling in red.
16
Tides
Low Tide
High Tide
 Regular rise and fall of
ocean water caused by
gravitational
attraction between the
Earth, moon, and sun.
 Most coastal locations
experience two high High Tide
tides and two low
tides per day.
Low Tide
Reference:
http://csep10.phys.utk.edu/astr161/lect/time
17
/tides.html