Ocean Currents and Salinity

Overview

In part one of this two-part lesson students work in pairs to explore the effects of salinity on ocean stratification using a simple plastic shoebox-sized container in which they create a mini-ocean environment. Students will apply what they learn in the lab setting along with information gained in several online articles to a basic understanding of the Global Conveyor Belt and its effect on global climate.

Part Two is available here: Investigating Earth's Hydrosphere: Ocean Currents and Temperature

Objectives

The objective of this lesson is to answer the following essential questions:

• How does salinity affect ocean density?
• How do differences in ocean salinity affect ocean stratification?
• How do differences in ocean salinity contribute to the Global Ocean Conveyor Belt System?

Lesson Preparation

1. Students should have had prior lessons on density concepts.
2. Before completing the lab students should read the article, "Salinity" developed by Windows On The Universe (see Resources section). This article can be accessed at three different reading levels and in Spanish. In this lesson students will create a mini-ocean system in a clear box to determine how salinity can affect ocean density and stratification. Students will add various amounts of salt to three different water samples, color each sample with food coloring, pour them one by one into a clear box and finally observe the profile of the overall system.
3. Students should read the journal and watch the movie "Going On A Sea Cruise", by PolarTREC educator Lisa Seff (see Resources section) to get an overview of how ocean salinity and temperature data are collected by researchers in the field.

Procedure

Procedure 1: Preparing the ocean water

1. Label the large beaker "Water #1"
2. Pour 500 mL of room temperature water into this beaker.
3. Add 1.5 teaspoons of salt and gently stir/swirl until all of the salt dissolves.
4. Use the salinity probe as directed by your instructor to determine the salinity of Water #1.
5. Write the salinity of Water #1 into the data table.
6. Add 50 mL of room temperature water to one of the small beakers.
7. Label this beaker "Water #2"
8. Add .25 teaspoons of salt and gently stir/swirl until all of the salt dissolves.
9. Use the salinity probe as directed by your instructor to determine the salinity of Water #2.
10. Write the salinity of Water #2 in the data table.
11. Add 3 drops of blue food coloring to Water #2 and swirl gently until mixed throughout.
12. Add 50 mL of room temperature water to the other small beaker.
13. Label this beaker "Water #3"
14. Do not add any salt to this beaker. The salinity will be 0ppt. Write the salinity into the data table.
15. Add 3 drops of red food coloring to Water #3 and swirl gently until mixed.

Procedure 2: Creating your ocean environment

1. Place 2 blocks under the corners at one end of your clear box so that the box is stable but tilted as shown in Diagram #1 (see 'Procedure 2', attached)
2. Take the temperature of Water #1 and write the temperature in the Data Table. Carefully pour Water # 1 into the box. You should have several inches of the box bottom that are not covered with water as shown with the arrow in the profile view Diagram #2 (see 'Procedure 2', attached)
3. Let the water rest for a minute.
4. Take the temperature of Water #2 and write the temperature in the Data Table. Carefully and slowly pour Water # 2 into the box in the area not covered with water just above the wooden blocks.
5. Let the water rest for a minute then move so your eyes are level with the water in the container and draw the profile view you see into Diagram #3 (see 'Procedure 2', attached)
6. Take the temperature of Water #3 and write the temperature in the Data Table. Carefully and slowly pour Water # 3 into the box in the area not covered with water just above the wooden blocks.
7. Let the water rest for a minute then move so your eyes are level with the water in the container and draw the profile view you see into Diagram #4 (see 'Procedure 2', attached)

Extension

1. Complete the complementary lesson 'Investigating Earth's Hydrosphere: Ocean Stratification, Currents and Temperature' (available through the PolarTREC website: www.polartrec.com)
2. Read the articles 'Ocean Water Properties' by the University of Rhode Island and 'Salinity' by NASA Science Earth, 'A Chilling Possibility' by NASA Science News and 'Global Conveyor Belt' by NOAA Ocean Service Education. The NOAA article also includes several animations the students should watch.
3. Alternatively, if educators would like to access articles on salinity available in different reading levels and in Spanish they should go to 'Salinity, Density of Ocean Water and Thermohaline Circulation' by Windows To The Universe. Use the links at the top of each webpage to change the reading level or language. Complete the corresponding survey: Ocean Water Properties and the Global Conveyor Belt.

Resources

• Center For Microbial Oceanographic Research & Education Ocean Conveyor Belt (http://cmore.soest.hawaii.edu/education/teachers/science_kits/ocean_conveyor_kit.htm)
• 'Going On A Sea Cruise' PolarTREC Journal and Video (http://www.polartrec.com/expeditions/oceanographic-conditions-of-bowhead-whale-habitat/journals/2012-09-02)
• 'Ocean Water Properties' by University of Rhode Island (http://www.hurricanescience.org/science/basic/water/)
• 'Salinity' by NASA Science Earth (http://science.nasa.gov/earth-science/oceanography/physical-ocean/salinity/)
• 'A Chilling Possibility' by NASA Science News (http://science.nasa.gov/science-news/science-at-nasa/2004/05mar_arctic/)
• 'Global Conveyor Belt' by NOAA Ocean Education (http://oceanservice.noaa.gov/education/kits/currents/06conveyor2.html)
• 'Salinity' by Windows To The Universe (advanced level-the level and language of this article can be changed by clicking on the appropriate link at the top of the page) (http://www.windows2universe.org/earth/Water/salinity.html&edu=high)
• Thermohaline Circulation: Global Ocean Conveyor by Windows To The Universe (advanced level-the level and language of this article can be changed by clicking on the appropriate link at the top of the page) (http://www.windows2universe.org/earth/Water/circulation1.html&edu=high)

Assessment

Students will be evaluated through the use of the accompanying lab questions and student worksheet.

Credits

This lesson was adapted by PolarTREC and Springs School Educator Lisa Seff from lesson materials originally developed by the Center for Microbial Oceanographic Research and Education. For the original lesson plan "Ocean Conveyor Belt" and additional resources such as PowerPoints, lesson extensions and self-contained lesson plan kits that educators may borrow for classwork go to the following link: C-MORE Ocean Conveyor Belt (http://cmore.soest.hawaii.edu/education/teachers/science_kits/ocean_conveyor_kit.htm)