8.16.2: Chapter Questions

Study Question

1. What are the major energy sources for the surface currents and the thermohaline circulation of the oceans?
2. Why doesn’t a wind-driven current flow in the same direction as the wind that causes it?
3. Wind-driven Ekman transport moves surface water across the oceans. How does this lead to geostrophic currents that continue to flow even if the winds abate? Why don’t geostrophic currents flow in the same direction as the Ekman transport?
4. Subtropical gyres are present in each ocean and each hemisphere in the latitudes between the trades and westerlies. Why? Would they exist if the Earth were totally covered by oceans? Why or why not?
5. Why do the subtropical gyres rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere?
6. How are upwelling and downwelling caused in the oceans, and why are they important? Where would you expect to find upwelling and downwelling areas in the oceans? Why?
7. What factors affect coastal currents but not deep-ocean currents?
8. Why are the deepest water masses in the oceans formed at high latitudes? Why are they not formed in the Indian and North Pacific oceans?
9. Why is there no pycnocline in most high-latitude regions of the oceans?
10. Why are temperature and salinity the two most important tracers of water masses?

Critical Thinking Questions

1. You might have heard it said that because of the Coriolis deflection, water going down a bathtub drain will swirl in opposite directions depending on whether the drain is located in the Northern or Southern Hemisphere. Do you think this is true? Explain why or why not.
2. Imagine that the viscosity of water was much higher, so that it flowed more like syrup. (a) Would the Ekman spiral and Ekman transport be different? If so, how would they be different and why? (b) Would there still be geostrophic currents? If so, how would they be different?
3. If seawater had a maximum density at 4°C, how would the deep water layers be different from those of today? Where would deep water masses be formed?
4. If we were to build a solid causeway across the Pacific Ocean from Seattle to Tokyo, how would the surface currents in the North Pacific Ocean be affected, and how might this affect the climate of Japan, Alaska, and California?
5. If the Earth were covered in water except for the North American continent, would there be geostrophic gyres? If so, where? What would the current pattern be in the Southern Hemisphere?
6. Discuss why you would expect the Gulf Stream to slow down and Europe to be colder if the rate of formation of North Atlantic Deep Water was reduced.
7. Why is there no geostrophic gyre in the Mediterranean Sea?
8. Global climate may change in the next few decades, with the average temperature of the ocean surface waters increasing by as much as several degrees. (a) Hypothesize what might happen to the thermohaline circulation of the oceans as a result. (b) Speculate on what would be the effects on the intensity, geographic distribution, and frequency of upwelling of water from below the permanent thermocline. Explain your reasons for these speculative changes.
9. From what you have learned about ocean circulation, what do you think would be likely to happen to the atmospheric concentrations of carbon dioxide if the carbonate compensation depth (CCD) were to migrate to shallower depths? How long would you expect it to take for these changes to occur? Explain why.
10. If the hypothesized global warming does indeed occur, the Arctic ice pack may melt completely. (a) How would this affect the bottom water mass of the Arctic Ocean? (b) How might it also affect the characteristics of bottom water masses in the other oceans? (c) What other changes in ocean circulation might be caused? (d) Would these changes be significant during a normal human’s lifetime, or would they take thousands of years to occur? Explain the reasons for your answer.