Chapter 16
The Dynamic Ocean
16.1 OCEAN CIRCULATION
Surface Circulation
• Ocean currents are masses of ocean water
that flow from one place to another
• Surface currents – movements of water that
flow horizontally in the upper part of the
ocean’s surface
– Develop from friction btw the ocean and the wind
that blows across its surface
Gyres
• Huge circular moving current systems
dominate the surfaces of the oceans
• 5 Main ocean Gyres
– N. Pacific Gyre
– S. Pacific Gyre
– N. Atlantic Gyre
– S. Atlantic Gyre
– Indian Ocean Gyre
• Coriolis effect – deflection of currents away
from their original course as a result of Earth’s
rotation
• Due to Earth’s rotation, currents are deflected
to the right in the N. Hemisphere & to the left
in the S. Hemisphere
• 4 main currents within each gyre
Ocean Currents & Climate
• When currents from LL regions move into HL
they transfer heat from warmer to cooler
areas on Earth
• As cold water currents travel toward the
equator, they help moderate the warm
temperatures of adjacent land areas
• Play a big role in maintaining Earth’s heat
balance
Upwelling
• Rising of cold water from deeper layers to
replace warmer surface water
• Wind-induced vertical movement
• Brings greater concentrations of dissolved
nutrients to the ocean surfaces
Deep – Ocean Circulation
• Density currents – vertical currents of ocean
H2O that results from density differences in
the H20 masses
• Increase in seawater density can be caused by
a decrease in temperature or an increase in
salinity
A Conveyor Belt
Warm H20
flows toward
poles
Cold, deep
water
upwells
Density
increases
Temperature
drops &
salinity
increases
Dense H20
moves
toward
equator
The cycle
repeats
Upwelled
H20 warms
16.2 WAVES & TIDES
Waves
• Energy traveling along the boundary btw
ocean and atmosphere
• Most ocean waves obtain their energy &
motion from wind
• Top of wave = crest
• Trough = separate crests
• Wave Height = vertical distance btw trough &
crest
• Wavelength = horizontal distance btw 2
successive crests (or 2 successive troughs)
• Wave period = the time it takes one full wave
(one wavelength) to pass a particular spot
• The height, length, & period depend on 3
factors:
– Wind speed
– Length of time the wind has blown
– Fetch (distance that the wind has traveled across
open H20)
• Circular orbital motion allows energy to move
forward through the H20 while the individual
water particles that transmit the wave move
around in a circle
• When waves approach shore, H20 becomes
shallower & influences wave behavior (“feels
the bottom” at depth = to half of its
wavelength)
Tides
Tide-Causing Forces
• Results from the gravitational
attraction exerted upon Earth
by the moon (and the sun)
• Gravity & Inertia produce
tides
• Gravity attracts the Earth &
moon
• Inertia = tendency of moving
objects to continue in a
straight line (keeps Earth &
moon from crashing into each
other
Tidal Cycle
• Tidal range – difference in
height btw successive high
& low tides
• Spring tides – tides that
have the greatest tidal
range due to the alignment
of the Earth – moon – sun
• Neap tides – lowest tidal
range
• Each month = 2 spring tides
& 2 neap tides
Tidal Patterns
• 3 main tidal patterns
– Diurnal Tides
• 1 high tide & 1 low tide each tidal day
– Semidiurnal Tides
• 2 high tides & 2 low tides each tidal day
– Mixed Tides
• Large inequality in high water heights, low water
heights, or both
16.3 SHORELINE PROCESSES &
FEATURES
Forces Acting on the Shoreline
• Waves along the shoreline are constantly
eroding, transporting, & depositing sediment
• Wave Impact
• Abrasion
• Wave Refraction
– Bending of waves
– Wave energy is concentrated against the sides &
ends of headlands that project into the H20,
whereas wave action is weakened by bays
– https://www.youtube.com/watch?v=G1FIBuybN78
• Longshore current – near shore current that
flows parallel to the shore
• Turbulence allos longshore currents to easily
move the fine suspended sand & to roll larger
sand & gravel particles along the bottom
Erosional Features
• Shoreline features that originate primarily
from the work of erosion
• Sediment that is transported along the shore
& deposited in areas where energy is low
produce depositional features
• Wave-Cut Cliffs & Platforms
• Sea Arches & Sea Stacks
Depositional Features
•
•
•
•
Spits
Bars
Tombolos
Barrier Islands – narrow sandbars parallel to
the coast (separate from coast) (3-30 km
offshore)
Stabilizing the Shore
• Groins, breakwaters, & seawalls are some
structures built to protect a coast from
erosion or to prevent the movement of sand
along a beach
• Can be built parallel to shoreline
• Beach nourishment is the addition of large
quantities of sand to the beach system