MIT Massachusetts Institute of Technology

Will an Ice Cube Melt Faster in Freshwater or Saltwater?

William Andrake
Science teacher
Swampscott Middle School
Swampscott, MA

With an often unexpected outcome from a simple experiment, students can discover the factors that cause and influence thermohaline circulation in our oceans. In two 45 minute class periods, students complete activities where they observe the melting of ice cubes in saltwater and freshwater, using basic materials: clear plastic cups, ice cubes, water, salt, food coloring, and thermometers. There are no prerequisites for this lesson but it is helpful if students are familiar with the concepts of density and buoyancy as well as the salinity of seawater. It is also helpful if students understand that dissolving salt in water will lower the freezing point of water. There are additional follow up investigations that help students appreciate and understand the importance of the ocean’s influence on Earth’s climate.

Bill Andrake has been a classroom science teacher, mainly at the middle school level, for over thirty years. His educational background and passion is in the study of marine biology and thus he often looks for ways to bring ocean science into his curriculum. Additionally, he feels this brings relevance and meaning to his lessons as he teaches students who live in a seaside community. 

From Woods Hole Oceanographic Institution - The Ocean Conveyor: Includes an animation that explains how thermohaline circulation works along with its importance to global climate.
http://www.whoi.edu/main/topic/ocean-conveyor 

From Woods Hole Oceanographic Institution – Fresher Ocean, Cooler Climate A less-salty North Atlantic Ocean Could Cool Northern Winters. Lonny Lippsett . Originally published online September 14, 2005 : In print Vol. 44, No. 2, Sep. 2005.
http://www.whoi.edu/oceanus/feature/fresher-ocean--cooler-climate

From Woods Hole Oceanographic Institution Is Global Warming Changing the Arctic And Will Polar Changes Trigger Climate Shifts beyond the Arctic? Lonny Lippsett . Originally published online January 23, 2006.
http://www.whoi.edu/oceanus/viewArticle.do?id=9206

From the National Oceanic and Atmospheric Association - The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity. Provides an introduction to thermohaline circulation and the global ocean conveyor belt.
http://oceanservice.noaa.gov/facts/conveyor.html 

From NOAA’s Climatic Data Center: NOAA Paleoclimatology - What caused the Younger Dryas? Younger Dryas was an abrupt change in climate as a result of a disruption to the thermohaline circulation in the North Atlantic about 14,500 years ago. This led to a period of colder climate that lasted about 3000 years.
http://www.ncdc.noaa.gov/paleo/abrupt/data4.html

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