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.