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Lesson 6:
Ocean Layers I
Chemical Oceanography
We have been learning about ocean
chemistry
What are two important cycling nutrients we have
learned about?
N&C
Name one way human activities affect each of
these nutrients.
What is a Dead Zone?
2
Salinity is another important part of ocean
chemistry
1.
2.
3.
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Salinity is a measure of the amount of dissolved
salts in water
Salinity is not homogenous (uniform) across the
Earth’s oceans
Both salinity and temperature affect the density of
seawater
Factors that influence salinity
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
4
What factors do you think might influence salinity?
Three primary factors influence salinity:
1. Freshwater input - High rates of freshwater input
(river inflow to the sea; melting ice) will decrease
salinity
2. Evaporation - High rates of evaporation will
increase salinity
3. Precipitation - High levels of rainfall will decrease
salinity
Salinity is variable across the ocean
Salinity is highest
in the mid -latitudes
and lowest at the
equator and highlatitudes
Photo: NASA
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Why is salinity important?
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Salinity is one factor that controls the density
of ocean water
What happens when water at different depths
has different densities?
Layers of water will form
Formation of layers is part of the reason we
have ocean currents
Lesson 7:
Ocean Layers II
Physical Oceanography
Last class we learned about salinity
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
How does salinity affect the density of water?

What other variable affects the density of water?
Ocean Layers
1.
2.
3.
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There are three layers in the ocean
Temperature typically gets colder as you move from
the surface of the ocean down through the middle
layer of the ocean.
In the very deepest parts of the ocean, temperature
and salinity tend to be uniform
Let’s take a journey down through the
ocean’s layers
Temperature (oC)
5
50
20
Depth (m)
The ocean has three
layers

The surface layer is on
top, the thermocline in
the middle, and the deep
ocean on the bottom
30
surface
thermocline
1000
2000
10
10

deep ocean
(Mid-Latitudes)
The surface layer
(also known as the mixed layer)


Temperature (oC)
5
10
20
30
mixed
50
Depth (m)
The upper surface of the
ocean is called the mixed
layer
Wind and other forces stir
or “mix” this upper layer of
water to form a relatively
constant temperature
throughout
thermocline
1000
deep ocean
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The thermocline
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Temperature (oC)
5
10
20
30
mixed
50
Depth (m)

The thermocline is a
layer of water where
temperature changes
rapidly with depth
In the thermocline,
the water quickly gets
colder the deeper you
go
This layer separates
the warm, surface
layer from the cool,
deeper waters
thermocline
1000
deep ocean
Deep Ocean

Below the thermocline is the
deep ocean
Temperature (oC)
5
10
20
30
mixed

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But here in the deep ocean,
salinity and temperature do
not change much as we
move downward and
become nearly constant
50
Depth (m)

Water here is cold, dense
and salty
thermocline
1000
deep ocean
What is the pycnocline?
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Pycnocline refers to an area where density changes
rapidly with depth
Seawater density is determined primarily by
temperature and salinity, though the influence of
temperature is often greater
Temperature and salinity tend to remain constant
below the pycnocline