填空题 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 1 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, while crystals of salt would be left behind; this, by the way, is how much of the table salt we use is actually 2 .
The opposite of evaporation is precipitation, such as rain, by which water is 3 to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas of high rainfall 4 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 5 water by precipitation of runoff.
Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat 6 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 alter is associated 7 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 8 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 9 a result of this 10 process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of oceans of the world.
A. with B. fresh C. added
D. and E. obtained F. until
G. or H. as I. freezing
J. higher K. incur L. before
M. in N. as O. cause