The Ocean in Motion: Wind-Driven Gyres and the Deep Overturning · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Two engines move the ocean

Science · Earth's Systems · ages 17-18
Name ______________________   Date ____________

  1. Three parcels of seawater compete to sink. Which one wins?

    • Warm and fresh
    • Warm and salty
    • Cold and salty

  2. What drives surface currents, and what drives the deep loop?

    • Wind at the surface, density differences below
    • Fish migration at the surface, tides at depth
    • Waves at the surface, wind at depth

  3. Surface currents stream in straight lines exactly downwind.

    Circle one:   True   False

  4. In a tank with no wind, salty water meets fresh water. What happens?

    • Salty water sinks and slides underneath
    • Fresh water dives below the salty layer
    • Both layers freeze in place at once

  5. What does the name thermohaline circulation tell you?

    • It is paced by tides and waves together
    • It is driven by heat and salt setting density
    • It is stirred by wind over hot sand

  6. The deep loop takes centuries per lap. What does that imply for climate?

    • The deep ocean never affects climate
    • Changes made now echo for generations
    • Surface currents will halt within years

  7. The ocean absorbs a pulse of extra heat today. When will the deep loop fully answer?

    • By next week, as surface currents race
    • Never, since heat cannot enter water
    • Centuries from now, not this year

  8. A student says gyres prove water ignores rotation and follows wind directly. What is wrong?

    • Wind never touches the ocean surface
    • Rotation steers the flow into closed gyres
    • Gyres appear only in tanks, never in oceans
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Two engines move the ocean W1-mt_ZaWclUQ-fh-s1

  1. Cold and salty · Cold and salty water is densest, so it plunges deepest.
  2. Wind at the surface, density differences below · The surface answers to wind while the deep answers to density.
  3. False · Rotation steers the flow sideways into closed gyres.
  4. Salty water sinks and slides underneath · Denser salty water drops while fresher water rides on top.
  5. It is driven by heat and salt setting density · Thermo points to heat and haline to salt, the two density controls.
  6. Changes made now echo for generations · Slow overturning stores today's heat and carbon for a very long time.
  7. Centuries from now, not this year · Deep water moves on a centuries timescale, so its reply is slow.
  8. Rotation steers the flow into closed gyres · Gyres exist precisely because rotation bends the wind-driven flow.
Worksheet · LightMySky