Oceans
Seas of Life
What are Oceans?
• List characteristics of the oceans:
– Large
– Waves
– Tides
– Salt water
– Plant and animal life
– Deep
What Are Ocean Waves?
• Ocean waves are movements where
water particles alternately rise and
fall.
How Do Waves Move?
• Water waves have two motions:
– The forward progress of the energy of
the wave.
– The circular motion of the water
particles as they rise and fall.
Wave Motion
Parts of Waves
• Crest = the top of a wave
• Trough = the bottom of a wave
How Are Waves Measured?
• Wave Length (Frequency)= the
distance from crest to crest.
• Wave Height (Amplitude)= the
distance from crest to trough.
How Do Waves Break?
• In open water waves roll.
• Waves break in shallow water as the
bottom of the wave has friction with
the ocean floor, but the top continues
at the same speed.
Effects of Breaking Waves
• Surf is the turbulent water caused by
breaking waves.
• Swash is the motion of water up the
beach and backwash is the water
running back down the beach and under
the next wave.
• Rip currents are strong narrow currents
that flow straight out to sea through the
surf zone.
Topography of the Sea Floor
• The crust of the sea floor is covered in many
places with layers of sediment.
• Terrigenous sediment is land sediment that
has settled on the ocean floor.
• Pelagic sediment is sediment made up of finegrained clays and skeletons of microscopic
organisms.
– This covers 75% of the ocean bottom and can take
up to 50 years to settle.
• Oozes are sediments of microscopic shells.
Ooze
s
Topography of the Sea Floor
Continental Shelf is a gently sloping surface
which extends under the ocean from the
shoreline to a depth of about 100-200 meters.
Continental Slope is relatively steep, extending
downward as deep as 2 km from the shelf.
Continental Rise is a wedge of sediment that
extends from the lower part of the slope to the
deep ocean floor.
Sea Floor Topography
• Abyssal plains are the flat regions of the
deep ocean floor at the base of the rise.
• Submarine canyons are v-shaped
valleys that run across continental
shelves and down continental slopes.
• Mid-ocean ridges are undersea
mountain ranges in the ocean basins.
• Trenches are deep ocean chasms
parallel to the edge of a continent or
island arc.
Sea Floor Topography
• Seamounts are volcanic mountains
rising 1000m above the ocean floor over
a hot spot.
• Guyots are volcanic islands that have
stopped growing and have been flattened
by wave action.
Atol
How Do Waves Form?
• Waves generally form in one of three
ways:
– Wind
– Underwater earthquakes
– Large amounts of ice or land falling into
the water.
How do Waves Form?
Wind Waves
• Waves are usually formed by wind
creating friction with the surface of
the water.
– With high enough wind speed a wave
forms.
– Increased wind speed = increased wave
height.
How Do Waves Form?
Wind Waves continued
• Fetch = the distance that wind blows
over the surface of the water.
– Increased fetch = increased wave
height.
– Therefore the largest waves form on the
biggest bodies of water with the
strongest, longest prevailing winds.
How Do Waves Form?
Underwater Earthquakes
• As underwater earthquakes shift the
ocean floor, very large waves called
tsunamis form as great amounts of
water rise and fall around the fault
line.
How Do Waves Form?
Landslides
• As large amounts of land/ice hit the
water at one time, very large waves
called mega-tsunamis form as great
amounts of water is pushed out of
the way.
Beaches
• A beach is a strip of sediment (usually
sand or gravel) that extends from the lowtide line to a cliff or zone of permanent
vegetation.
• The beach face is the section the waves
are constantly pounding.
• Just offshore there is usually a marine
terrace, a wide, gently sloping platform
that may be exposed at low tide.
• The berm is the wave-deposited upper
part of a beach that is usually dry.
Berm and Terrace
What Are Tides?
• Tides are long, slow waves that
result in the alternate rise and fall
of the surface level of the oceans.
– Tides can change sea level by up to
60 feet.
What Are Tidal Pools?
• Tidal pools form as high tide water
collects and is trapped when the tide
drops.
Tidal Pools
How Do Tides Occur?
• Tides are caused by
– the gravitational pull of the moon
and sun on the earth,
– The rotation of the earth.
What is the Shape of the
Earth?
• The gravitational forces acting on the
earth flatten the oceans of the earth
into an oblate sphere.
Types of Tides
• High tide is the highest level the water
reaches.
• Low tide is the lowest level the water
reaches.
• Spring tides are more severe (higher high
tides and lower low tides than normal).
• Neap tides are less severe (lower high
tides and higher low tides than normal).
Spring Tide
• Spring tides occur when the
gravitational forces of the sun and the
moon pull on the earth in the same
way.
– This combination of forces makes the earth
more oblate (less round) and causes
higher than normal high tides and lower
than normal low tides.
Neap Tide
• Neap tides occur when the gravitational
forces of the sun and the moon pull on
the earth at right angles to each other.
– This combination of forces makes the earth
more round and causes lower than normal
high tides and higher than normal low
tides.
What is the Intertidal Zone?
• The intertidal zone is an
ecosystem that exists in the area
of coastline between the high
tide line and the low tide line.
Life In The Intertidal Zone
• Threats to life are:
– Being dried up by the sun
– Being eaten by birds and animals
– Being washed out to sea
Adaptations for Life in the ITZ
• Organisms adapt to the wet/dry cycle
of the ITZ by various means:
– Locomotion
– Shells
– Grip
– Maintaining moisture
– Hiding/burrowing
Adaptive Organisms
Limpet
Erosion and Deposition by
Wave Action
• Longshore Drift is the movement of
sediment parallel to the shore as waves
strike the shore at an angle.
• Groins are built to protect beaches that are
losing sand from longshore drifting.
• Jetties are rock walls designed to protect the
entrance of a harbor from sediment
deposition and storm waves.
Jettie
s
Groins
Coast and Coastal Features
• The coast is all the land near the sea,
including the beach and a strip of land
inland from it.
• Coasts change, due to drowning by
glacial meltwater or tectonic forces,
resulting in irregular shorelines with
valleys that become short, deep, narrow
bays.
• Headlands are the points of land
between the valleys.
Headlands
What is Wave Refraction?
• An irregular coast with bays
separated by headlands can
gradually be straightened by wave
action.
• Shallow water slows waves off the
headlands while those same waves
move faster through the deep bays.
• This bending of the wave is called
wave refraction.
Headland Erosion
Wave Erosion and Deposition
Wave Trains
Coastal Features Formed by
Wave Erosion of Headlands
• Sea cliffs are steep slopes that erode
as waves undercut them.
• Stacks are erosional remnants of
headlands, and sea arches are
bridges of rock left after shoreline
erosion.
• Fjords are long, deep, steep sided
bays formed by glaciers.
• Estuaries are drowned river valleys.
Sea Cliffs
Tidal Estuary
Stacks, Fjiords, Arches
Coastal Features Formed by
Wave Erosion of Coasts
• Sandbars are ridges of sand that parallel the
shoreline, usually underwater.
• Barrier islands are sandbars that reach above
sea level.
• A spit is a finger-like ridge of sediment that
extends out into the open water.
– A spit with a curved end is called a hook.
• Baymouth bars are ridges of sediment that cut
off an earlier open bay from the ocean.
• Tombolos are bars of sediment that connect a
former island to the mainland.
Sandbars, Spits, Baymouth bars and Tombolos
How Did The Oceans Form?
• Water came from volcanoes (water
vapor) into the air. Over millions of
years this water vapor cooled, and
condensed, then precipitated out to
form the oceans.
Where Did The Salt Come
From?
• Once the oceans formed, the water cycle
began.
– The constant runoff, along with erosion,
dissolved many elements and minerals and
deposited them in the oceans.
– Other elements were added to the atmosphere
from volcanoes.
– The most abundant elements were sodium,
chlorine, silicone and calcium.
What is Salinity?
• Salinity is the measure of the amount
of solids (primarily salts) dissolved
in the ocean water.
– On average, in every 1000 grams of salt
water there is 35 grams of dissolved
solids. (35 parts/1000)
Salinity of the Oceans
Does Not Change
• Salinity remains constant because:
– Constant adding from volcanoes,
erosion, runoff etc.
– Constant removal by plants and
animals, and solids forming on the
bottom.
– Addition and removal occur at the same
rates.
How Does Salinity Support
Life?
• Salinity is harmful to humans
yet it supports marine life.
How?
– Calcium forms bones and
shells
– Silicone forms shells
– Oxygen and carbon dioxide
dissolved in the water is used
for respiration of animals and
What Are Ocean Currents?
• In a current the water particles flow in one
direction.
– Like in rivers and oceans.
• Ocean currents distribute solar energy around
the globe.
• There are several types of ocean currents.
– Surface currents
– Density currents
– Turbidity currents
Surface
Currents
• A surface current is a movement
of water that affects only the
upper 100 feet of seawater.
– Most are caused by winds.
• Example is the Gulf Stream
How Do Surface Currents
Affect Life?
• Surface currents affect life through:
– Weather
– Marine life = food supplies
Surface Currents Affect
Weather
• Weather: surface currents
affect the climates by
distributing the heat energy of
the oceans around the globe.
– Warm water from the tropics is
brought north as cold polar water
is brought south.
Surface Currents Affect Marine
Life
• Most life in the oceans exists
close to the surface because:
– Ocean plants need light for
photosynthesis.
• Light only penetrates upper 100-200
feet
– Animals live near surface where food
sources exist.
Classification of Marine Life
• Marine organisms are classified by
the way they move.
• Marine organisms are classified as
either plankton, nekton, or benthos.
What are Plankton?
• Plankton = are organisms that drift.
– most are microscopic.
– plankton depend on dissolved
substances in the water to exist.
– plankton exist where “food” is and
therefore travel with the prevailing
currents.
What are Nekton?
• Nekton = are organisms that swim
(fish and animals).
– Since these organisms can swim they
can search for food.
– These organisms still tend to use the
currents as their supply of food.
What are Benthos?
• Benthos are organisms that live on
the ocean floor.
• These organisms do not swim and
some, such as corals, stay in one
place their entire life. Others, such
as snails and crabs, crawl along the
ocean floor.
Some Benthos
What Are Density Currents?
• Density currents are the movement
of water that occurs when dense
seawater moves toward areas of less
dense seawater. (usually vertical)
• Density currents are affected by
temperature and salinity.
Affects of Temperature on
Currents
• Freshwater freezes faster (less density).
• As the freshwater freezes it increases the
salinity of the surrounding seawater.
• The more dense seawater sinks and
pushes the less dense seawater away
resulting in a current.
Upwelling
• Upwelling is an interruption in a density
current.
– This usually is the upward movement of cold
water.
– This happens when strong surface winds carry
warm surface water away allowing the cold deep
water to come to the surface.
Coastal Upwelling
What are Turbidity Currents?
• Turbidity currents are dense
mixtures of water and sediment that
are pulled downslope by gravity like
huge avalanches. These are a major
cause of canyon erosion.
– Turbidites are the deposits made by
turbidity currents.