EarthLabs > Earth System Science > Lab 5: It's All Connected: Global Circulation > 5B: Message in a Bottle

Lab 5: It's All Connected: Global Circulation

Part B: Message in a Bottle


In Part A, you traced the pathways of wind and water into and out of your study region. Now, you will use computer simulations to track ocean currents.


Stop and Think

1: Imagine dropping a message in a bottle into the ocean at a given location and observing where the object would end up as a result of surface currents. Based on the pathways you traced in Part A, where do you think your bottle would end up?



Use a computer model to test your prediction. The model uses simple physics equations of motion and information about ocean surface currents from historical monthly ship drift data to predict the motion and pathways of objects adrift at sea.
  1. Click Ship Drift Model to open the model in a new window. This model only includes circulation of currents. It does not include effects of wind/waves or the dynamics of the floating object. The model assumes that the drifter is a small object floating at the surface, and that it has a density similar to that of ocean water. This model does not apply to sailing or motorized boats or ships.
    • You should see a map of the world with arrows depicting the mean or average direction of currents at the ocean surface. The direction of an arrow indicates the direction of the current and an arrow's color indicates the speed of the current. A color scale below the map shows you how to convert each color to a speed in meters per second.

    Checking In

    • What is the range of current speeds (in meters/second) shown on the map?
    • What is the range of current speeds (in miles/hour) shown on the map? Is the fastest surface current speed faster or slower than the average human walking speed (3 miles/hour)? HINT: 1 mile = 1609.344 meters


  2. Look carefully at the world map to find the current speeds that correspond to the different colored arrows. Make a table like the one below and fill in the empty boxes with current speeds in meters/second.
    Ocean Currents Table


  3. Simulate dropping your message in a bottle into the water using the closest ocean access point to your study region as your starting location.
    • Find the place on the map where you want to drop your bottle into the ocean. Move your mouse to that location and click on the map. A second window with a map showing the tracks of five drifters will pop up.
    • Find and write down the starting longitude and starting latitude for your model.

    In the example shown below, the start click was made near the southeast coast of the United States. A square, black outline box marks the beginning of the drifter's voyage (labeled in the image with the word "Start"). The colored tracks (purple, blue, red, orange, blue) follow five drifters under the influence of variable currents through five years. A color-coded , diamond-shaped, outline box marks the end of the track. The five different tracks show the approximate effects of the ocean surface current variability. Coordinates on the map below use degrees of longitude (horizontal scale) and degrees of latitude (vertical scale). The starting point has a longitude near -80 degrees and latitude near 31 degrees.
    Drift path example



  4. Estimate the end locations for the five drifters and write the numbers in a table like the one below.
    drifter locations table


  5. Stop and Think

    2: How well does your prediction of where your message in a bottle would end up agree with the computer model? Explain.

    3: What events and activities in other parts of the globe could affect your region? Describe events and activities that are caused by people (such as making dams) and those caused by nature (such as volcanic eruptions).

    4: What events and activities in your region could affect other parts of the globe?


  6. Experiment with dropping the drifters in different locations around the world to see how the drifters' pathways compare. Try dropping the drifters into the ocean near the following locations:
    • New England
    • the west coast of Australia
    • California
    • Venezuela
  7. Stop and Think

    5: Compare and contrast the paths of these drifters with those of drifters dropped into the ocean near your study region.

    6: Why do you think there are international laws for dumping waste/trash/chemicals in the ocean, rather than just local laws? Do these laws only need to extend to nearby neighboring countries? Explain.


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