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Oceanography
Chapters 15 & 16
15.1 - The Oceans

Oceanography - The study of the
Earth’s oceans.
 In the late 1800’s the British Challenger
became the 1st research ship to explore
below the ocean’s surface.
Modern Oceanography

Modern research ships use SONAR to
map the seafloor features
 SONAR stands for
SOund Navigation And Ranging
Origins of the Oceans

Has Earth always had oceans?
 Several geological clues indicate that
we have had oceans since the
beginning of geological history.
 Earth is 4.6 billion years old.
Where did the water come from?

Scientists hypothesize that water could
have come from 2 sources:
– they collided with Earth and
released water on impact, over time these
impacts filled the oceans
 Volcanism – significant quantities of gases
were emitted into the air, gases were
mainly water vapor that condensed quickly
into water
 Comets
Distribution of Earth’s Water

97% salt water
 3% freshwater
 Percentage of ice has varied on Earth
from near 0 to 10 percent of the
hydrosphere
 Sea level - the level of the ocean’s
surface
Distribution of Earth’s Water

Sea level has risen and fallen by
hundreds of meters in response to
melting ice and expanding glaciers.
 Tectonic forces that lift and lower the
seafloor also account for variations in
sea level.
 Global sea level rises at 1 to 2 mm per
year because of melting glaciers.
Changes in global sea level
What will happen in the future?
The Blue Planet




Approximately 71% of Earth’s surface is
covered by oceans.
Average depth is 3800 meters
Most land is in the northern hemisphere
where oceans account for 61%
Southern hemisphere has 81% oceans
Major Oceans

Three major oceans: Pacific, Atlantic,
and Indian
 Pacific is largest - roughly half of Earth’s
seawater
 Atlantic - 2nd largest
 Indian - 3rd largest
Earth’s Major Oceans
Sea Ice

The Arctic and Antarctic Oceans are
covered by vast expanses of sea ice
 In the summer ice breaks up
 In the coldest part of the Arctic and
Antarctic Oceans there is no summer
thaw and ice is generally several meters
thick and can be more than 1000 km
wide.
15.2 - Seawater

96.5% water
 3.5% salts
 Most abundant salt in the sea is sodium
chloride (NaCl)
Chemical Properties of Seawater



Salinity - measure of the amount of dissolved
salts in seawater
Oceanographers express salinity as grams of
salt per kilogram of water, (parts per
thousand… ppt )
Total salt content 35ppt or 3.5%
Variations in Salinity

Average salinity is 3.5%, however
actual salinities vary on a global scale
 Subtropical regions have higher salinity
(3.7%). Why?
Because evaporation > precipitation
 Equatorial regions have lower salinities.
Why?
Because evaporation < precipitation
 Polar regions 3.2% - 3.3% due to the
melting of sea ice.

The Mediterranean Sea and the Red
Sea can be as high as 4%.
 The Dead Sea has the highest salt
concentration of any sea in the world.
Physical Properties of Seawater

The presence of various salts causes
the physical properties of seawater to
be different than freshwater.
 Seawater
is more dense than freshwater
 Temperature affects density, colder water
is more dense
 Differences in salinity causes the freezing
point of seawater to be lower when
compared to freshwater
 Freshwater is 0°C, seawater is -2°C
Absorption of Light

Intensity of light decreases with depth
 Water absorbs light, so oceans are dark
 Light sufficient for photosynthesis only
exists in the top 100 m of the ocean
Ocean Temperature Layers

Temperatures range from -2°C to 30°C
 Average ocean temperature is 15°C
 Temperature dramatically decreases
with depth
 Dark waters below 1km have fairly
uniform temp of less than 4ºC
Ocean Layering (3 distinct layers)
 Surface
layer - first 100 m
 Thermocline
- 100 - 1000 m, characterized
by rapidly decreasing temp with depth
layer – Cold water sinks to the
bottom because it is more dense
A) 1000m and below
B) cold and dark
C) temps near freezing
 Bottom
15.3 - Ocean Movements

Wave - a rhythmic movement that
carries energy
 Generated by wind over the water’s
surface
Wave Characteristics

Highest point of wave is the crest.
 Lowest point of wave is the trough.
 Vertical distance between crest and
trough is the wave height
 Crest to crest is the wavelength
Wave Height

Wave height depends on three things:
 Wind
speed
 Wind duration
 Fetch – the distance the wind blows across
the water
Breaking Waves

Waves lose energy as they approach
the shore due to friction with the ocean
bottom.
 That friction between the shallow
shoreline and the water causes surface
waves to move ahead of deeper waves
and collapse.
Tides

Tides are the periodic rise and fall of
sea level; cycles every 24h and 50 min
 Difference in high and low tide varies
from place to place
 Gulf
of Mexico tidal range is less than 1 m
 New England can be as high as 6 m
 Highest range is 15 m in the Bay of Fundy
off of Nova Scotia
Causes of Tides

Basic cause of tides are the gravitational
attraction among the Earth and the Moon
 The moon pulls water away from Earth
Water bulges on the side of
the Earth nearest the moon.
Causes of Tides

Spring tides - occur when the Moon is either
full or new; when Sun, Moon and Earth are
aligned; large tidal ranges

Neap tides - cause small tidal ranges when
the moon is either in first or third quarter
Ocean Currents

Surface currents - any continuous flow of
water along a broad path in the ocean.
 Surface currents move fast, 100 km/day
 Primarily driven by the wind
Importance of Surface Currents

Moves drifting organisms from place to
place
 Carries eggs and larvae of organisms
that have external fertilization
 Brings food and oxygen
 Carries away waste and pollutants
 Warms continents
 Influences weather and climate patterns
16.1 - Shoreline Features

Ocean waves change the shape of a
shoreline by eroding rock materials and
depositing sediments.
 Beaches are long stretches of coastline
that are lined with wide areas of
sediment; usually sand or small
pebbles.
 The size of the sediment depends on
the energy of the waves striking the
coast.
Shorelines Formed by Erosion
Sea stacks – rock tower formed by wind
and wave erosion
 Sea arch – weaker rock is eroded away
by wave and wind erosion.

Shorelines Formed by Deposition
Spit – narrow bank of sand that projects
into the water from a bend in the
coastline
 Barrier island – long ridges of sand
deposited by currents that run parallel to
the shoreline
 Tombolo – a sea stack connected by a
sandbar
