MOTION IN THE
OCEAN
Waves, Tides, and Currents
Waves

A disturbance which
moves through or
over the surface of a
fluid

Mostly caused by
winds
(Also earthquakes,
volcanoes, grav. pull)

Form of great energy
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
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
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

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
What Causes Tides?
1. Gravitational pull of
sun & moon on Earth
• Moon closer, therefore
> effect
• Like magnet, pulls water
away from surface
= TIDAL BULGE
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
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
Importance of Tides
• Expose & submerge orgs
• Circulate water in bays &
estuaries
• Circulates food, wastes, etc
• Trigger spawning (grunion,
horseshoe crab)
Currents
• What are currents?
- “Rivers” of circulating water
• Causes
- Wind
- Rotating Earth
- Density Changes
Surface Ocean Currents
• Broad, slow drifts; never
cross equator
• Wind generated; circular
patterns
•
Coriolis Effect
- N. Hemis – clockwise; Right
- S. Hemis – counterclockwise; Left
• 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
Deep Ocean Currents
Flow
beneath surface; cross
equator
Move North to South

Separated from surface
currents by boundary
called a “Thermohaline”
(diff in densities)
Importance Of Deep Currents

Upwelling
• Brings deep water to surf.
• Circulates nutrients up
• Moves plankton & larvae