2019年10月13日托福阅读真题+题目+答案：Ocean Currents

2019年10月13日托福阅读真题+题目+答案：Ocean Currents

Wind moving across the surface of ocean water produces a frictional drag that forcefully pulls along the surface waters, creating ocean currents. The water moves at an angle to the wind, since it is deflected (curved) by the rotation of Earth toward the right in the Northern Hemisphere and to the left in the Southern Hemisphere; this is known as the Coriolis effect. The pattern of ocean surface currents is similar, but not identical, to the pattern of prevailing winds. The speed of ocean currents is usually only about 2 percent to 3 percent of the wind speed. An average wind speed of 10 meters per second would therefore produce an ocean current moving at 30 centimeters per second. In the North Atlantic Ocean, current velocities may be as high as 200 centimeters per second.

Like atmospheric circulation, oceanic circulation has a vertical dimension. Generally, the surface and deep layers of ocean water do not mix because of differences in their temperature and salinity (the concentration of dissolved salts). The surface waters (those no deeper than 200 meters from the surface) are warmer and less saline, and therefore less dense, than the deeper, cooler ocean waters. When warm tropical surface currents reach polar regions, particularly the coasts of Antarctica and Greenland, the water loses heat to the surrounding environment and becomes cooler and denser. The waters cool off enough for ice to form, which increases the salinity of the unfrozen water. This combination of cooling and greater salinity increases the density of the water, which sinks to deeper layers. These dense, downwelling currents move toward the equator, carrying cold polar water toward the warmer tropical oceans.

These deep ocean currents connect with surface currents again at zones of upwelling, where deep ocean waters rise to the surface. Upwelling occurs where prevailing winds generally blow nearly parallel to a coastline, such as off the western coasts of North and South America.

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1.Why does the author state that "An average wind speed of 10 meters per second"?

A emphasize the variability of ocean current speed in different places

B provide an example of the impact the Coriolis effect has on an ocean current

C demonstrate the difference between the pattern of ocean currents and that of prevailing winds

D provide a specific illustration of the relationship between wind speed and the speed of ocean currents

2. According to paragraph 2 which of the following is true of surface water as compared to deep ocean water?

A. Surface water has a more stable temperature than deep ocean water.

B. Surface water has a lower concentration of salt than deep ocean water.

C. Surface water travels greater distances than deep ocean water.

D. Surface water flows toward the equator, while deep ocean water flows toward the poles.

3. According to paragraph 2, downwelling occurs in the polar regions because of

A. the greater impact atmospheric circulation has on oceanic circulation in polar regions

B. the greater depth of oceans in the polar regions

C. the increased salinity of water in polar regions due to ice formation

D. the particular characteristics of the coastlines of polar regions

。。。。余下托福阅读真题题目省略！

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