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Oceans
Introduction
• The “Blue Planet”
– Seventy-one
percent of Earth’s
surface is
represented by
oceans and
marginal seas
– Continents and
islands comprise
the remaining 29
The Oceans of Earth
About 7% of
the size of the
Pacific
The largest and
has the greatest
depth
About half the
size of the
Pacific and
not quite as
deep
Slightly smaller than the
Atlantic, largely a Southern
Hemisphere body
Earth’s Northern & Southern
Hemispheres
The Composition of Seawater
Composition of Seawater
• Salinity
– Salinity is the total
amount of solid
material dissolved
in water
– Typically expressed
as 0/00 or parts per
thousand (ppt)
– 350/00 is world
average
Composition of Seawater
• Salinity
– Anion + cation = a salt
• Salt = NaCl = Na+ + Cl• Na+ has a positive charge (cation)
• Cl- has a negative charge (anion)
Composition of Seawater
• Salinity
– What goes in must equal what goes out
• Addition of sea salts
– Chemical weathering of rocks on continents (cations)
– Volcanic eruptions / outgassing (anions)
Composition of Seawater
• Salinity
– What goes in must equal what goes out
• Addition of sea salts
• Removal of sea salts
–
–
–
–
Sea spray
Evaporites
Biologic processes
Magma at M.O.R.
Important Factors:
Precipitation
Evaporation
Freezing
Run-off
The Ocean’s Layered Structure
• Temperature and salinity change with depth
in the oceans
– A three-layered structure exists in the open
ocean
The Ocean’s Layered Structure
• Temperature and salinity change with depth
in the oceans
– Salinity variations with depth correspond to the
general three-layered structure described for
temperature
– Thermocline = zone of rapid temperature
change
– Halocline = zone of rapid salinity change
Features of the Ocean Floor
Mapping the Ocean Floor
• Bathymetry – Measurement of ocean depths
and the charting of the shape or topography
of the ocean floor
– Echo sounder (also called sonar)
– Multibeam sonar
– Measuring the shape of the ocean surface from
space
Mapping the Ocean Floor
• Three major topographic units of the ocean
floor
Continental Margins
• Classifications of ocean floor
– Continental Margins – the submerged outer
edge of a continent
– Ocean Basin – the deep seafloor beyond the
continental margin
Continental Margins
• There are two types of continental margins:
– Passive margins
• Also called Atlantic-type margins
• Face the edges of diverging tectonic plates.
• Very little volcanic or earthquake activity
Continental Margins
• There are two types of continental margins:
– Active margins
• AKA as Pacific-type margins
• Located near the edges of converging plates.
• Active margins are the site of volcanic and
earthquake activity.
Passive Continental Margins
1. Continental Shelf
2. Shelf Break
3. Continental Slope
4. Submarine Canyons
5. Continental Rise
Submarine Canyons and
Turbidity Currents
Graded Beds
Each layer grades from coarse at its base to
fine at the top.
back
Active Continental Margins
• Located primarily around the Pacific Ocean
• Continental slope descends abruptly into a
deep-ocean trench
• Accumulations of deformed sediment and
scraps of ocean crust form accretionary
wedges
• Some subduction zones have little or no
accumulation of sediments
An Active Continental Margin
Deep-Ocean Basins
• Features of the deep-ocean floor
–
–
–
–
–
Oceanic Ridges
Hydrothermal Vents
Abyssal Plains and Abyssal Hills
Seamounts and Guyots
Trenches and Island Arcs
Deep-Ocean Basins
Seamounts & Guyots
Deep-Ocean Basins:
Trenches
Mariana trench
the deepest
(11,020 m)
Peru-Chile trench the
longest ( 5900 km)
Ocean Sediments
Seafloor Sediments
• Particles entering the ocean
• Accumulate
– Rapidly on continental margin (pelagic)
– Slowly in the deep ocean (neritic)
• Reflect ocean history
Seafloor Sediments
• Thickness varies
– Thickest in trenches—Accumulations may
approach 10 kilometers
– Pacific Ocean—About 600 meters or less
– Atlantic Ocean—From 500 to 1000 meters
thick
• Mud is the most common sediment on the
deep-ocean floor
Seafloor Sediments
• Sediment can be classified by particle size.
– Waves and currents generally transport smaller
particles farther than larger particles.
Seafloor Sediments
• Types of seafloor sediments
–
–
–
–
Terrigenous sediment
Biogenous sediment
Hydrogenous sediment
Cosmogenous sediment
Studying Sediments
• How do scientists study sediments?
–
–
–
–
–
–
Deep-water cameras
Clamshell samplers
Dredges
Piston Corers
Core libraries
Seismic profilers
Studying Sediments
• What can scientists learn by studying
sediments?
– Historical information
– Location of natural resources, especially crude
oil and natural gas
Ocean Circulation
Surface Circulation Patterns
• Gyre Formation
– Water tends to pile
up in the direction
the wind is blowing
– Water pressure is
higher in the “piled
up” area
– Gravity pulls water
down slope
– Creates huge,
slowly moving
gyres
Surface Circulation Patterns
• Five main gyres
1.
3.
2.
5.
4.
Surface Circulation Patterns
• Deflected by the Coriolis effect
– To the right in the Northern Hemisphere
– To the left in the Southern Hemisphere
Surface Circulation Patterns
• Four main currents exist within each gyre
– A Western Boundary Current
– An Eastern Boundary Current
– Two Transverse Currents
Surface Circulation Patterns
• Western boundary
currents
– Narrow, fast and deep
– Move warm water
poleward
– Well defined boundaries
– Can create features like
eddies
– Little to no coastal
upwelling – nutrient poor
• Eastern boundary
currents
– Slow, shallow and broad
– Carry cold water to the
Equator
– Poorly defined boundaries
– Tend not to form eddies
– Upwelling common –
nutrient rich
Currents Within Gyres
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Surface Circulation Patterns
• Effects of Surface Circulation
– Climate
• Warm water currents bring warm, humid air to
higher latitudes
• Cold water currents bring cool, arid air to lower
latitudes
• Moderates global temperatures
Surface Circulation Patterns
• Effects of Surface Circulation
– Climate
– Wind-induced vertical circulation
• Upwelling is the upward motion of water.
– This motion brings cold, nutrient rich water towards the
surface.
• Downwelling is downward motion of water.
– It supplies the deeper ocean with dissolved gases.
Deep-ocean Circulation
Patterns
• Formation
– A response to density differences
– Factors creating a dense mass of water
• Temperature—Cold water is dense
• Salinity—Density increases with increasing salinity
– Called thermohaline circulation
Waves
Waves
• Wave anatomy
Note that the water molecules in the crest of the wave move in the same
direction as the wave, but molecules in the trough move in the opposite
direction.
Waves
• Energy transferred from one
water particle to another in
orbits
–
–
–
–
Causes the wave form to move
Called orbital wave
Occur between two fluid media
Progressive waves – waveform
moves forward
Waves
• Wavelength determines the size of the orbits
• Water depth determines the shape of the
orbits
• Two broad categories
– Deep-water Waves
– Shallow-water Waves
Waves
• Deep-water Waves
– Waves moving through water
deeper than half their
wavelength ( )
Waves
• Shallow-water Waves
– Water molecule orbits
“flatten” as they get close to
the bottom
– Water above seafloor cannot
move in a circular path
– Waves in water 1/20th their 
are shallow-water waves
Waves
Wind Waves Approaching a Shore
1.Wave train moves towards shore
2.Circular motion of water molecules is
interrupted
3.Wave slows as water becomes more shallow
4.Wave becomes too high for its wavelength
5.Water now moving faster than the wave
6.Wave breaks
7.Forms the surf
Beaches
and
Shoreline Processes
Beaches and Shoreline
Processes
• A beach is a zone of
loose particles that
covers a shore.
• Larger particles are
associated with more
sloped beach.
Beaches and Shoreline
Processes
• Sediment Sources
– Rivers and Streams
– Eroding beach cliffs – 5 – 10% of beach sand
– Sand from the seafloor immediately offshore
Beach Anatomy
beach
offshore
shore
nearshore
foreshore
Longshore
bar & trough
wave cut terrace
coast
backshore
Beaches & Shoreline Processes
• Wave erosion
– Erosion of shoreline by wave impact and
pressure
– Breaks down rock material and supplies sand to
beaches (minor amount)
Beaches & Shoreline Processes
• Wave refraction
– Bending of a waves
– Wave arrives parallel to shore
– Results
• Wave energy is concentrated against the sides and
ends of the headland
• Wave erosion straightens an irregular shoreline
Wave Refraction Along an
Irregular Coastline
Figure 10.12
Beaches & Shoreline Processes
• Longshore transport
– Beach Drift: sediment on beach moves in zigzag fashion via swash/backwash
– Longshore Current: current moves down
beach, caused by waves hitting beach at angle
• Flows parallel to the shore
• Transports sediments down the coast
• Moves substantially more sediment than beach drift
Beach Drift & Longshore Currents
Shoreline Features
• Erosional Features
–
–
–
–
–
Wave-cut cliff
Wave-cut platform
Marine terraces
Sea arch
Sea stack
Shoreline Features
• Depositional features
– Spit, baymouth bar, tombolo, & barrier islands
Stabilizing the Shore
• Shoreline erosion is influenced by the local
factors
–
–
–
–
–
Proximity to sediment-laden rivers
Degree of tectonic activity
Topography and composition of the land
Prevailing wind and weather patterns
Configuration of the coastline
Stabilizing the Shore
• Threats to the Sand Supply
– Flood control dams
– Southern California has 77 sand and gravel
quarries in stream channels
– Paved river channels – reduces channel
widening
– Seawalls and riprap reduce cliff erosion and
focus wave energy onto the beach
Flood Control Dams in
Southern California
Stabilizing the Shore
• Responses to erosion problems
• Hard stabilization—
Building structures
–
–
–
–
Sea Walls
Groins
Jetties
Breakwaters
• Alternatives to hard
stabilization
– Beach nourishment by
adding sand to the
beach system
– Relocating buildings
away from beach
– Returning to “natural”
channels
Stabilizing the Shore
• Erosion problems along U.S. Coasts
– Atlantic and Gulf Coasts
• Development occurs mainly on barrier islands
– Face open ocean
– Receive full force of storms
• Development has taken place more rapidly than our
understanding of barrier island dynamics
Stabilizing the Shore
• Erosion problems along U.S. Coasts
– Pacific Coast
• Characterized by relatively narrow beaches backed
by steep cliffs and mountain ranges
• Major problem is the narrowing of the beaches
– Sediment for beaches is interrupted by dams and
reservoirs
– Rapid erosion occurs along the beaches
Tides
Tides
• Changes in elevation of the ocean surface
• Caused by the gravitational forces exerted
upon the Earth by the
– Moon,
– and to a lesser extent by the Sun
Spring and Neap Tides
• Spring Tides
– During the period of a
new moon, the moon
and sun are lined up on
the same side of the
Earth
– Produces the greatest
range between high
water and low water
• Neap Tides
– Produced when the
moon is at a right angle
to the line of centers of
the Earth and the sun
– The range between
high and low water is
small
Tide Patterns
• Diurnal tide
– One high and one low tide per day
• Semidiurnal
– Twice occurring high and low tide
sequences
– High and low tides are both at the
same level
• Semidiurnal mixed tide
– Combination of diurnal and
semidiurnal tides patterns
– Each high tide reaches different
heights
– Each low tide falls to different levels
Tide Patterns
The worldwide distribution of the three tidal patterns.
Tidal Currents
• Mass flow of water
induced by the
raising or lowering
of sea level owing to
passage of tidal
crests or troughs
• Ebb current
• Flood current
• Slack water
Tides and Marine Organisms
• Intertidal Zone
– Where the land and sea
meet, between the high
and low tide zones.
– Organisms that live
here are adapted to
huge daily changes in
moisture, temperature,
turbulence (from the
water), and salinity.
Tides and Marine Organisms
• Grunions! (Leuresthes tenuis)
– Spawn from late February to early September
End