This document discusses the three main layers of the ocean - the surface layer, thermocline layer, and deep ocean layer. It provides details about each layer: 1) The surface layer or epipelagic zone is mixed by wind and currents, keeping temperatures relatively constant down to around 200m. 2) The thermocline layer lies below and temperatures drop rapidly with depth down to around 1000m, separating the warm surface waters from the cold deep waters. 3) Below the thermocline, the deep ocean layers of bathypelagic, abyssopelagic and hadalpelagic zones have cold, dense waters where temperature and salinity remain uniform with increasing depth.

1. Lesson 7:
Ocean Layers II
Physical Oceanography

2. Last class we learned about salinity
 How is salinity measured?
 How does salinity affect the density of water?
 What other variable affects the density of water?
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3. Today we’ll learn more about ocean
layers
1. There are three layers in the ocean
2. Temperature typically gets colder as you move
from the surface of the ocean down through the
middle layer of the ocean.
3. In the very deepest parts of the ocean, temperature
and salinity tend to be uniform
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4. Let’s take a journey down through the
ocean’s layers
 The ocean has three layers
 The surface layer is on top. The
surface layer is also called the
Epipelagic Zone.
 The thermocline in the middle,
which is made up of the
Mesopelagic Zone.
 The deep ocean is on the
bottom. The deep ocean can be
further divided into the
Bathypelagic, Abyssopelagic
and Hadalpelagic Zones.
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5. Let’s take a journey down through the
ocean’s layers
 The depth of each layer
can change based on
location and season
 Here, the thermocline
ranges from about 50m-
1,000m
 The majority of ocean
water (by volume) can be
found in the deep ocean
below the thermocline5

6.  The upper surface of the
ocean is called the mixed
layer or epipelagic zone.
 Wind and other forces stir
or “mix” this upper layer of
water to form a relatively
constant temperature
throughout
 Depending on weather,
season, and latitude, the
mixed layer typically ranges
from 10 – 200 m in
thickness
(Mid-Latitudes)
We’ll start our journey in the surface layer
(also known as the mixed layer or Epipelagic Zone)
1000
50
Temperature (oC)
5 10 20 30
Depth(m)
thermocline
mixed
deep ocean
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7. Let’s move down into the thermocline
 The thermocline is a
layer of water where
temperature changes
rapidly with depth
 The thermocline contains
the Mesopelagic Zone
 In the thermocline, the
water quickly gets colder
the deeper you go
 This layer separates the
warm, surface layer from
the cool, deeper waters
1000
50
Temperature (oC)
5 10 20 30
Depth(m)
thermocline
mixed
deep ocean
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8. What happens as we move below the
thermocline?
 Below the thermocline is the
deep ocean – containing
the Bathypelagic,
Abyssopelagic and
Hadalpelagic Zones
 Water here is cold, dense
and salty
 In the deep ocean, salinity
and temperature do not
change much as we move
downward – they become
1000
50
Temperature (oC)
5 10 20 30
Depth(m)
thermocline
mixed
deep ocean
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9. Don’t get confused with “clines”
 Remember that thermocline refers to a “gradient”
where temperature changes rapidly with depth
 Halocline is an area where salinity changes rapidly
with depth (halo refers to salt)
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10. What is the pycnocline?
 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
 Just as temperature and salinity influence seawater
density, the thermocline and halocline affect the
pycnocline
 Temperature and salinity tend to remain constant
below the pycnocline
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11. Student activity
Now, answer the multiple choice and short answer
questions on the assignment “Tips for the Bowl –
Ocean Layers.”
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