Science as Inquiry

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    Earth & Space Science

  • Structure of the earth system (5-8)
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  • Geochemical cycles (9-12)

    Science in Personal & Social Perspectives

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  • frozen Great Lakes

    The winter of 2003-2004 was bone-chillingly cold for many regions in the United States. One region especially hard hit has been the Great Lakes. December 2003 was a relatively mild month, with temperatures averaging as high as 5 degrees above normal. In January 2004, as is typical in the winter, the jetstream migrated southward allowing cold Arctic air to come in from Canada. Temperatures in January averaged 9 degrees below normal. With the plummeting temperatures, the Great Lakes have begun to freeze over, resulting in major impacts on life around the Great Lakes especially for maritime travel and commerce.

    The Great Lakes formed approximately 14,000 years ago as the glaciers that once covered North America began to retreat. The lake system accounts for 20% of the world's fresh water, making it the largest freshwater system in the world. It is made up of five lakes, Superior, Michigan, Ontario, Erie and Huron, and is bordered by eight states and two Canadian Provinces. The lakes are connected to each other by three rivers, St. Marys, St. Clair and Niagara, and the Straits of Mackinac. The St. Lawrence Seaway provides the outlet to the Atlantic Ocean. A series of locks, canals and channels allow ships up to 740 ft long to maneuver the Great Lakes.

    The Great Lakes are a major shipping gateway, especially for agricultural and mine products, and yet it's not unusual for Lakes Superior, Huron, and Erie to experience 70% or more ice coverage during the winter. The NOAA Great Lakes Atlas maintains daily average ice cover charts from 1973 through 2002 for Superior, Michigan, Ontario, Erie and Huron.

    How does the shipping industry deal with ice? Indeed, the locks between Lake Ontario and Montreal on the St. Lawrence River do close from late December to late March because of ice, but before and after this closed season, the Great Lakes have a couple of methods to ensure that maritime commerce can continue even with ice. The United States and Canadian Coast Guards employ icebreaking tugs, vessels, and buoy tenders to cut paths through the ice. They also rely on up-to-date ice data and ice prediction charts. Both the United States National Ice Center and the Canadian Ice Service produce ice charts that use an "egg code" to explain the ice conditions.

    The egg code is a unique symbol that can convey a lot of information in a compact form. The egg code is divided into four sections. The top section indicates how much ice coverage is in a certain are of the lake and is depicted in tenths. If the top number is 1, then 1/10th or 10% of the area has ice. The remaining three sections are read in columns and describe the thickness (section 2), type of ice (section 3), and the size of the chunk of ice or "ice floe" (section 4). Go to the Canadian Ice Service Egg Code page to see a detailed explanation of how to read an egg code.

    In the following data activity, we will analyze actual and predicted ice charts and use them to discuss wintertime shipping in the Great Lakes.


    Print out the following 2002-2003 ice charts from the National Ice Center:

    How did the predicted January ice maps compare with the actual December ice maps? How did the predicted March ice maps compare with the actual March ice maps? Did any lakes completely freeze over? Do you think the 2002-2003 winter was warmer than normal or colder than normal?

    As mentioned above, the Montreal/Lake Ontario locks open back up in late March. Do you think the lakes would have been free of ice by then? Look at the actual ice conditions for March 27, 2003 eastern lakes and western lakes. Which major ports would be most affected by the remaining ice?

    Now let's look at the 2003-2004 season. Print the following maps:

    How closely are the 2003-2004 predictions to the actual values? How do they compare to the 2002-2003 season? Notice that Lake Erie always seems to have the most ice, and yet it's the southern-most lake. Why might that be? (Hint: look at the depths of the lakes). Which ports would be affected by a frozen over Lake Erie?

    Print out the predicted ice maps for March 2004 for the eastern lakes and western lakes. Assume these maps show the ice conditions for when the Montreal/Lake Ontario locks resume business. On the maps, draw the easiest routes for ice cutters to clear a path to get from the St. Lawrence River to Toronto, Cleveland, Chicago and Duluth. Did your routes stay close to shore, or were they near the center of the lakes? Which routes had the most ice?

    For more related resources, visit the Bridge's Great Lakes page.

    If you have questions about the Data Tip of the Month or have suggestions for a future data tip, contact Lisa Lawrence, Bridge Data Project Manager.

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