Sinking Water: A Connection With Glaciers, Ocean Currents and Weather Patterns

Stanley Mraz, North Park Elementary School in Fridley, MN in the Colombia Heights School District.
Guided inquiry part of the lesson is based on an original activity from the FOSS Kit, Water, p. 16-18.
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In this investigation students will first observe that some objects float in water and some objects sink in water. An operational definition that FOSS encourages is that objects float in water if they are less dense than water and objects sink if they are denser than the water they are in. Then, students will investigate what happens when they lower a small vial of hot water colored with red food coloring into a cup of room temperature water. Next, the students will lower a vial of cold water colored with blue food coloring into a cup of room temperature water. Finally, through a guided discussion and a teacher demonstration through the use of a model of the ocean and a glacier, the students will see real-world application of the affects of melting glaciers of Greenland. Not only will they witness a rising sea level, they will also see that the enormous amount of cold water could push the North Atlantic ocean current into a different or lower position thus affecting the ocean current systems which are a critical part of driving our global climate.

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Learning Goals

This activity is designed for students to learn that warm water is less dense than room temperature water and that cold water is denser than room temperature water. Through teacher questioning, observation and critical thinking, the students will discover that this concept is critical to understand due to the impacts of global climate change impacting the world's glaciers. The students will view a large model of the Atlantic Ocean (aquarium) and an iceberg from Greenland (frozen blue food coloring on a large slab of ice). Students will understand how ocean levels will rise. Students will also learn the connection between cold glacial water with the change of ocean current movement and global climate change. Key vocabulary: density, ocean currents, glaciers, sea level, global climate change

Context for Use

This lesson can be conducted in either a classroom or a science lab. The lesson is for my 4th grade science class; but, due to the standards it meets, it could easily be a fifth grade lesson. In order to conduct the buoyancy and hot and cold water density experiments, a teacher will need at least 50 minutes. The glacier connection/extension is at least another 15 to 20 minutes depending upon the depth of the discussion. Equipment that will be needed are bins (one per four students) and a variety of objects to test. A vial of water (7 dram) with red food coloring, a craft stick and a rubber band to attach to the vial and a large cup of room temperature water to lower the vial in are all needed to do the warm density test. The cold density test requires the same set of objects with the exception of ice water and blue food coloring place in the vial. For the extension activity that makes real-world applications, the teacher will need to prepare in advance a "glacier" (blue food coloring and water frozen in a container or balloon) and have a large aquarium. A drawing of a city at near sea level could be prepared in advance.

Description and Teaching Materials

The First Part of the Lesson is Taken From Investigation 2, Part 2 of FOSS
Introduce the activity by giving students a variety of objects and have them predict which ones will float in their container of water and which ones will sink. After completing the buoyancy tests, determine with the class that if an object floats in water, the object is then less dense than the water. If it sinks, the object is than denser than the water. Next, introduce the hot-water challenge. Show the students how to attach a small vial to a craft stick with a rubber band. Fill the vial with hot water colored with red food coloring. Ask them what they think will happen when the vial is carefully lowered to the bottom of the cup of water that is at room temperature. After the experiment is completed and the results show that the hot red water rose, discuss with them why. Now do the same activity except switch the vial to very cold water with blue food coloring and lower it into another container of water. Remember to use a container of the same size. Again, make observations and discuss the results.
Application to Real World by Stan Mraz:
After the density portion of the lesson on how cold water is denser than warm water (FOSS Water Kit, P.16-18), the teacher asks the class, "We all learned that cold water is denser than warm water. As a result, cold water sinks. Why is this important to know?" After students volunteer their responses (or after a long period of silence), ask them, "Do you know what is happening to the temperature of our planet? Why is this happening? How will this rise in temperature impact plants, animals, and even our weather?" After you are satisfied with the discussion, show them the aquarium and tell them, "This is a model of our ocean. What do we call the elevation of our ocean? (Sea Level) I am going to draw a line with this transparency maker on the outside of the aquarium to represent the current level of our ocean on this model. Over here (the teacher could prepare in advance paper with drawn cut-outs of a city's buildings) I am going to quickly sketch on the outside of the aquarium some buildings to represent a city alongside the ocean. Can anybody name some cities near the ocean? Actually, most of our world's population lives quite close to an ocean!" After drawing or placing the prepared paper sketch of the city, "unveil" (from a hidden cooler) a huge iceberg. This must be prepared in advance by mixing blue food coloring in with the water in a large balloon or "glacier shaped" container that is placed in a freezer. It is best to handle the glacier with gloves to prevent staining of the hands! Ask the students, "What do you think this large piece of ice represents in the model?" After a brief discussion on glaciers and students sharing what they already know about glaciers ask them, "If this glacier is on this huge slab of bedrock (place the iceberg on the lab table), it does not move very fast. How could rising temperatures cause it to move faster towards the ocean?" After students have given a variety of explanations, give the following demonstration. First describe how warming temperatures cause the glacier to melt and form pools of water on top of the ice. Demonstrate this by pouring a bit of water in a variety of places. Then ask, "What do you think happens to some of these pools of water on top of the ice?" After a few students volunteer their thoughts state, "Many pools tunnel to the bottom and eventually, when melting continues to run off, moulins form. Moulins are glacial waterfalls. These waterfalls lubricate the ice where it meets the bedrock. What do you think this does to the glacier? Right, it makes the glacier slide easier to the ocean. What do you think this will do to the ocean?" Demonstrate by gentle sliding the glacier into the aquarium. Ask, "What do you notice that happened to the water level of the ocean? The students will easily see that the water level rose dramatically and the city next to the ocean is now underwater. In addition, the students (with maybe a few teacher clues) will notice that water (colored blue) is coming off of the bottom of the glacier and sinking. Ask the students, "What happens to cold water that we discovered in our science lesson?" Then, ask them how they think this melting could affect our global climate. Describe to them that the earth has ocean currents (like they might have seen in the movie, Finding Nemo) and that the cold water pushing down on the North Atlantic current could seriously change the climate because the climate is partly regulated by the movements of ocean currents.

Extra Fascinating Facts:
The ocean currents are all connected like a giant conveyor belt. In the North Atlantic, 5,000,000,000 gallons of cold glacial water are coming off of Greenland every second. Greenland is covered by 630,000 cubic miles of ice. That's enough to raise global sea levels by 23 feet.

An Inconvenient Truth, 2006 Paramount Pictures.

Schiele, Edwin. NASA: Ocean Motion and Surface Currents.

Rudolf, John Collins. The Warming of Greenland, published January 16, 2007, New York Times.

Teaching Notes and Tips

Depending upon the freezer, it often will take at least two days to freeze a significant amount of water that is at least 2 liters in volume. A gallon milk jug with colored water filled slightly under the handle will work well. Bring the "iceberg" to school in a well-insulated cooler and keep it a surprise until the moment arises. Wearing gloves in the class while handling the "iceberg" prevents staining and keeping the hands from becoming numb!

After the extension is over, make a list of inquiry entries with the class concerning the situation. Also, it's best to empower the students with positive messages and not gloom and doom. Here are some ideas of easy things they can do to make a difference. See what other ideas they can come up with from a federal government level to an individual level.

A Few Ideas from
Change a light: Replacing one regular light bulb with a compact florescent light will save 150 pounds of carbon dioxide a year.
Drive less: Walk, bike, carpool or take metro transit more often. You'll save one pound of carbon dioxide for every mile you don't drive.
Recycle More: You can save 2,400 pounds of carbon dioxide per year by recycling just half of your household waste.
Use less hot water: It takes a lot of energy to heat water. Use less water and less hot water by installing a low-flow showerhead. Wash your clothes in cold or warm water instead of hot water.
Turn off the electric devices not being used such as DVD players and computers.
Plant a tree: A single tree will absorb one on of carbon dioxide over its lifetime.
Adjust your thermostat: Moving your thermostat down just 2 degrees in the winter and up 2 degrees in summer could save about 2,000 pounds of carbon dioxide per year.
Check your tires: Keeping your tires properly inflated can improve your gas mileage by more than 3%.
Avoid products (such as bottled water) that use a lot of packaging! You can save 1,200 pounds of carbon dioxide if you cut down your garbage by 10%.


An informal assessment can be given by observing students' understanding of buoyancy by having a checkoff list (not included) of predictions and results. A quick formal essay could be given by having students coloring the water movement of a picture of a vial with warm water submerged in a container of room temperature water. They would also color a picture of a vial of cold water submerged in a container of room temperature water. Finally, they could write a short descriptive paragraph explaining how this concept connects with what is happening in the real world.

Standards Explain what would happen to a system such as a wetland, prairie or garden if one of its parts were changed. In this lesson the system changed is the ocean currents. Understand that different models can be used to represent natural phenomena and these models have limitations about what they can explain. Aquarium and iceberg model represent the phenomena of sinking cold water.

References and Resources