2008年大学英语四级巅峰阅读培训(第二十七讲)

科普：自然世界 348词 建议作题时间：8分钟
　　If the salinity of ocean waters, that is, how much salt the ocean waters contain, is analyzed, ti si found to vary only slightly from place to place. Neverthelee, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation — change of liquid water to water vapor. In this manner, the salinity is increased, since the salts stay behind. If this is carried to the extreme, of course, white crystals of salt would be left behind; this is how much of the table salt we use is actually obtained.
The opposite of evaporation is precipitation, such as rain, by which water is added to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas of high rainfall or in coastal regions where the rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by evaporation, or decreased by the additon of fresh water by precipitation or runoff.
　　Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea, salinity is somewhat lower than in other oceanic areas.
　　A third process by which salinity may be altered is associated with the formation and melting of sea ice. When seawater is frozen, the dissolved materials are left behind. In the manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water.
In the Weddell Sea, off Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of the oceans of the world.
　　1. There is no _________ of the salinity between different places in the sea.
　　2. Precipitation makes the salinity of an ocean decrease becouse it __________.
　　3. Where is the process of evaporation strongest?
　　4. What happens to the salt in the seawater when it is frozen?
　　5. The densest water formed in the Weddell Sea is an example of _________.
　　◆难句突破◆请翻译下面两句话：
　　①Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation.
　　分析：复合句。主干是the ocean salinity is higher。两个where引导的定语从句分别修饰regions 和the world
　　答案：通常，在太阳照射强烈的热带地区，海水咸度比在其他蒸发现象不那么强烈的地区要高一些。
　　②In the Weddell Sea, off Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water.
　　分析：复合句。主干是the densest water is formed。其中，as….是结果状语，which引导的定语从句作process的后置定语，which在从句中做主语。
　　答案：在南极洲附近的德威尔海，海水结冰现象导致了地球上限度的海水的形成，它增加了冷水的咸度。