What happens to ice in water?

Contributed by Sharon Browning, Cornelia Harris, Kristine DeLong, Mellie Lewis

Topic: The properties of water in the ice and liquid phase as it relates to convection in the ocean and density driven circulation.
Course type: Introductory level college students (non-science majors) and high school students.

This activity teaches Climate Literacy Essential Principle 2: Climate is regulated by complex interactions among components of the Earth system

Goals

Students should be able to do the following:

• Understand the relationship between temperature, density and the phases of H₂O; water and ice.
• Make connections to how disruptions to the overturning circulation system can cause abrupt climate change when thermohaline circulation ceases.

Description

Water has unique properties, density is one of the most important as it is related to convection and density driven circulation in the ocean. Liquid water is densest at 4ºC, not the solid ice phase, which is lighter. This explains why ice floats in the ocean and cold, dense liquid water sinks. Saltwater adds another dimension by increasing the density of water. The combination of temperature and salinity produces a overturning, density driven circulation in the ocean or thermohaline circulation.

Convection circulation is the thermally driven with warm, less dense water rising and cold, dense water sinking, similar to boiling water on the stove. A short video demonstration of thermohaline circulation, called wind in a bowl illustrates the warm rising and cold sinking convection circulation. The video also shows that ice floats and the meltwater from the ice sinks. This demo could be conducted live in class.

The lesson should include a discussion of the properties of water, density and convection circulation with a demonstration of the properties. Then have the students work together on a problem in which warmer water than the bowl water is added to the surface of water. What would happen to the circulation? Then discuss how thermohaline circulation can be disrupted and how this relates to abrupt climate change and examples from the past such as the Younger Dryas. This can be demonstrated by adding warmer water than the bowl water (20ºC) with green food coloring to the water bowl.

Teaching Materials

Power Point file with data (PowerPoint 311kB Jun14 11) and Worksheet (Microsoft Word 25kB Jun15 11).
Data and the activity are from the NASA Aquarius Mission ( This site may be offline. ) . Students use the images in the PowerPoint file to answer the questions in the worksheet.

Assessment

Pre activity quiz
This salinity quiz by NASA can be used to test students' knowledge of salinity and density prior to the lessons. Using the results from the quiz, educators can assess the misconceptions some students may have regarding salinity and the properties of water.

Post Activity project
The students are broken into groups to work together to solve the problems based on the what they learned about water, density, and salinity. The students are asked to form a hypothesis of what would happen if freshwater was added to the surface of the ocean at various temperatures from 0ºC to 20ºC. The groups would then compare their results. This could be done as a jigsaw if time permits.

If the class is conducting the demo live, then the students could add green dry to water at their temperature to test their hypothesis.

References

Data for this activity from NASA Aquarius Mission
Ocean Currents and Sea Surface Temperature ( This site may be offline. ) - classroom activity by My NASA Data Lesson Plans
http://www.globe.gov/tctg/earth_la_seaphen_s5.pdf?sectionId=26 Cloud Watch (pdf file) by GLOBE
Salinity facts from the NASA Aquarius Mission
Science: Ocean Circulation & Climate from the NASA Aquarius Mission
Salinity & The Water Cycle – Overview - classroom activity from the NASA Aquarius Mission
Wind in a bowl - instructions for demo and video of the demo