EarthLabs > Earth System Science > Lab 5: It's All Connected: Global Circulation > 5A: Tracing Pathways

Lab 5: It's All Connected: Global Circulation

Part A: Tracing Pathways

Global ocean surface currents: blue lines show cool currents; red lines show warm currents. Click image for larger view. Image source: Teachers' Domain, Examine Global Surface Currents, published December 17, 2005, retrieved on January 11, 2010,
Circulating wind and ocean currents distribute energy and matter all around the globe. Surface currents are primarily driven by wind and Earth's rotation. Earth's rotation causes the pathway of both air and water to appear to curve rather than travel in a straight line. This is known as the Coriolis effect. Because the Earth spins counterclockwise (when viewed from above), the Coriolis effect causes winds to be deflected eastward (right) in the northern hemisphere and westward (left) in the southern hemisphere. Ocean currents behave similarly, but can also be deflected by continents or other landmasses, which causes the water to move in circular patterns called gyres. Watch this short video for a demonstration of how the Coriolis effect works.

Deeper ocean currents, often called "thermohaline circulation," are controlled by temperature (thermo) and salinity (haline). Saltier water is more dense and therefore sinks. The motion of this heavier water results in vertical mixing of the ocean water that drives deep ocean currents. You might also hear this process referred to as the "global ocean conveyor belt" because the currents generated by this cold water mixing travel around the world. Ocean currents move heat from warm tropical latitudes toward colder polar latitudes, transport nutrients that sustain marine life, and aid ocean travel. Ocean currents may also carry trash, pollutants, or other drifting debris up to thousands of miles. Fortunately, one person's trash can sometimes truly be another person's treasure.

In January 1992, 29,000 bathtub toys spilled into the ocean when a storm hit a ship traveling from Hong Kong to Tacoma, Washington and knocked a shipping container into the sea. Ten months later, plastic ducks, turtles, frogs, and beavers began washing ashore near Sitka, Alaska. The distribution of this debris may have seemed like a disaster to some, but scientist Curt Ebbesmeyer saw it as an exciting opportunity to study the paths of ocean currents. In fact, Curt Ebbesmeyer made an entire career out of tossing objects into the water to see where they end up.

  1. Although it is very difficult to trace the exact path of a particular parcel of air or ocean water and anything it might contain, we can use average wind and water patterns to explore how different regions around the world are connected to one another. Look at this interactive map of global surface currents and then answer the Checking In questions below.

    Checking In

    Answer the following questions to check your understanding of the information contained in the interactive global surface currents map.
    • Look at the direction of the surface currents in the oceans and at the direction of the wind. What evidence do you find that wind influences the direction of the surface currents in the oceans?
    • What pattern can you see in the direction of the global winds? Look at global winds near the equator, in the middle latitudes, and in the polar regions.
    • Notice the location and flow of warm and cold ocean currents. Why do you suppose that currents flowing toward the equator are generally cool while currents flowing away from the equator are warm?

  2. Look at the black outline map of the world and the world maps of average ocean currents and average winds in January and July given to you by your instructor. If you do not already have copies, download and print them now using the links below.
  3. Locate the Earth System study region you defined in Lab 4, on the black outline map map of the world and draw a box around it.

  4. Trace the flow of water from your study region. Start upstream at the source, then move downstream through your study region to an ocean, noting the names of bodies of water and the regions through which it passes.

  5. Using the world maps of average ocean currents and average winds to guide you, draw the pathways of wind and water into and out of your region on the black outline map: from where it meets an ocean, across that ocean to other continents, to around the globe. NOTE: You may want to use pencil at first; then use different colored pens or pencils to distinguish wind direction and water currents from each other.

  6. Write the geographic names of regions along the water's pathway and through which the wind passes.

  7. Answer the following Stop and Think questions about wind and water pathways through your study region.

    Stop and Think: Wind

    1: What are the regions from which wind blows into your region? Write down real geographic names (for example, write the name of a mountain chain, not just "mountains").

    2: What might the wind be bringing into your region? Think about the places the wind is coming from, what happens there, what lives there. Think about dust, insects, tiny seeds, smoke, air masses of cooler or warmer temperatures, and moisture. Be specific in your responses.

    3: When wind blows out of your region, what region does it blow into? Again, write down real geographic names.

    4: What might the wind be carrying out of your region? Is it the same as what it brought in? Be as specific as you can about what is being carried, and where it goes.

    Stop and Think: Water

    5: What are the regions from which water flows into your region? Write down geographic names.

    6: What might the water be bringing into your region? Be as specific as you can.

    7: When water flows out of your region, what region does it flow into? Again, write down geographic names.

    8: What might the water be carrying out of your region? Be specific.

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