If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, 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-conversion 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, by the way, 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 rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by evaporation or decreased by the addition 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 this 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 deepest portions of the oceans of the world.
13. What does this passage mainly discuss?
14. Which of the following is NOT true after the formation of ocean ice?
15. Why does the author mention the Weddell Sea in the last paragraph?
16. What can be inferred about the water near the bottom of oceans with ices?
问题1选项
A.The change in oceanic salinity
B.The processes of sea water
C.The formation of our table salt
D.The conversion of sea water
问题2选项
A.The salt is still in the water.
B.The heavy water sinks.
C.The water becomes denser.
D.Water salinity decreases.
问题3选项
A.To suggest that it has salinity variation.
B.To compare Antarctic waters with Arctic waters.
C.To indicate the location of deep waters.
D.To give an example of cold-water salinity.
问题4选项
A.It moves very quickly.
B.It is relatively warm.
C.Its salinity is relatively high.
D.It is relatively cold.
13. 主旨大意题。文章的第一句If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place.（如果对海水的盐度进行分析，就会发现各地的盐度差别很小。）但是有些小的变化是重要的，最后再说明了导致海洋的盐度变化的基本过程有三个：蒸发、降水和冰。文章一直围绕着盐度变化进行阐述。因此A选项“海洋盐度的变化”正确，符合题意。B选项“海水的过程”，C选项“我们食盐的形成”，D选项“海水的转化”均与题意不符，可排除。故选A。
14. 推理判断题。定位在倒数第二段When seawater is frozen, the dissolved materials are left behind. In this manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared.（海水冻结时，溶于其中的物质被留了下来。这样，在新形成的海洋冰正下方的海水会比在冰块形成之前有更高的盐度。）由此可知海洋冰形成后附近水域的盐度会上升，而不是下降，因此D选项“盐度降低”错误。同理可知A选项“盐还在水里”，C选项“水变得更浓了”正确。B选项“重水下沉”定位在最后一段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.（在南极洲附近的威德尔海，海洋中最稠密的水是由于这种冻结过程而形成的，这种冻结过程增加了冷水的盐度。）可知This heavy water sinks这种重水下沉也与海洋冰的形成有关。故选D。
15. 推理判断题。定位在最后一段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 deepest portions of the oceans of the world.（在南极洲附近的威德尔海，海洋中浓度最高的水是由于这种冻结过程而形成的，这种冻结过程增加了冷水的盐度。这种重水下沉，在世界海洋最深的部分被发现。）还是在对第三种导致海洋的盐度变化的过程海洋冰的举例，因此答案选D选项“举冷水盐度的例子”正确，符合题意。A选项“表明它有盐度变化”，与题意不符，可排除。B选项“把南极水域和北极水域进行比较”属于无中生有，可排除。C选项“指示深水的位置”偷换主语，非深水而是重水下沉。可排除。故选D。
16. 推理判断题。根据原文In this manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared.（这样，在新形成的海洋冰正下方的海水会比在冰块形成之前有更高的盐度。）和the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water.（由于这种冻结过程，海洋中最密集的水形成，增加了冷水的盐度）由此可推理出在海洋冰底下的海水浓度会更高。因此C选项“它的盐度相对较高”正确，符合题意。A选项“它移动得很快”，B选项“海水会相对暖和”，D选项“海水相当冷”，均未涉及，不符合题意，可排除。故选C。
