What causes thermohaline
circulation?
Check Your Slide Notes
 Earth has one ocean.
 Five main regions of the ocean are the Atlantic Ocean,
the Pacific Ocean, the Indian Ocean, the Arctic Ocean,
and the Southern Ocean.
 Thermo means related to heat or temperature and
haline means related to salinity.
 Thermohaline currents are caused by differences in
temperature and salinity.
Check Your Slide Notes
 High salinity water cools and sinks in the North Atlantic.
 Water returns to the surface in the Pacific and Indian
Oceans through the process of upwelling.
 Not all ocean surface water has the same salinity.
 Salinity tends to be greater in warmer waters.
 The thermohaline ocean conveyer explains why there
is a circumpolar deep water current.
Consider the following…
 What provides the thermal energy that drives the
conveyer?
 Why does the conveyer explain the differences in
climate between New Jersey and Oregon?
 What other factors might explain why New Jersey and
southern California do not have the same climate
although both are on a warm ocean current?
 Does the conveyer explain monsoons in the Indian
Ocean region? Explain.
Consider the following…
 Why does the thermohaline current curve instead of
moving in a straight line from the tropics to the polar
regions?
 Why is the curvature in opposite directions in the
northern and southern hemispheres?
 Whose name is given to this phenomenon?
 What happens when a denser liquid and a less dense
liquid meet?
Consider the following…
 What other factor causes ocean surface currents?
(Hint: It is caused by pressure differences related to
unequal heating of Earth’s surface.)
 What would happen to the climate of northern Europe if
the Gulf Stream shut down? (Hint: It has happened in
the past.)
 What would cause the conveyer to slow or change
patterns? (Hint: This answer could involve tectonic
changes occurring over millions of years,
extraterrestrial events, or changes in Earth’s
atmosphere.)
Modeling Earth Systems
You will use
 a density tank that has two compartments separated by
a removable divider
 food coloring
 cold freshwater, warm freshwater, cold saltwater, warm
saltwater
Each group will be assigned two combinations of water.
Test Variables
Density will depend on
 Salinity
 Temperature
We test 6 combinations that mimic conditions on Earth.
Two combinations will test the temperature only. Two
combinations will test the salinity only. Two
combinations will test temperature and salinity. All
combinations model a particular location.
Test Combinations
 Warm freshwater/Cold freshwater
 Warm salt water/Cold salt water
 Warm salt water/Cold freshwater
 Warm freshwater/Cold salt water
 Cold freshwater/Cold salt water
 Warm freshwater/Warm salt water
Form a Hypothesis
 Which variable will be more dense?
 Why do you expect a certain outcome?
 Use the hypothesis starter if you need
help.
The ___________________ will be less
dense than ___________________
because
_________________________________
___.
Procedure
1. Pour one variable into the left side of the density tank.
2. Pour the other variable into the right side of the
density tank.
3. Carefully remove the tank divider.
4. Observe what happens and record your observations.
5. Explain what you observed.
What happened?
Conditions
 Warm freshwater/Cold freshwater
 Warm salt water/Cold salt water
 Warm salt water/Cold freshwater
 Warm freshwater/Cold salt water
 Cold freshwater/Cold salt water
 Warm freshwater/Warm salt water
Outcome
Where in the world…
 Describe what you observed.
 Explain what you observed.
 What location in the world does your density tank
model? (Hints: Cold and warm freshwater would be
found together in a great deep lake.) Explain your
decision.
Where in the world…
Be ready to discuss the “consider the following…”
questions and to research more about climate and
factors that cause climate change.