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When we analyze the salt salinity(盐浓度) of ocean waters, we find that it
varies 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. In this manner, the salinity is increased, since the salt
stays behind. If this is carried to the extreme, of course, white 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 (稀释) 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.
Normally, in hot 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, the densest water in the ocean 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 portion of the oceans of the world.
26. This passage mainly tells us about_______.
A. the analysis of the salinity of ocean waters
B. the causes of the variation in oceanic salinity
C. the importance of the changes in oceanic salinity
D. the different forms of salts in ocean waters
27.It can be known from the passage that increase in the salinity of ocean
water is caused
by______.
A. melting of sea ice B. precipitation
C. evaporation D. supplement of salt
28.Which of the following is not the cause of the decrease in the oceanic
salinity?
A. Precipitation. B. Rain and snow.
C. Formation of ice. D. Addition of water by rivers.
29.Which of the following statements is TRUE according to the passage?
A. Oceanic salinity has great effect on sea life.
B. Many factors combine to cause changes in oceanic salinity.
C. The movement of the water is related to the amount of salt.
D. The temperature of the water has much to do with the oceanic
salinity.
30.The purpose of mentioning the Weddell Sea is_______.
A. to give an example of cold-water salinity
B. to point out the location of deep waters
C. to make a comparison between hot-water salinity and cold-water
salinity
D. to show that the water in the Weddell Sea varies in salinity from place
to place
答案：26. B 27. C 28. C 29. D 30. A
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发表于 2016-7-11 18:45:54