新東方優美背誦短文50篇 Unit39:The Salinity of Ocean Waters

39 The Salinity of Ocean Waters

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.

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 sea water is frozen, the dissolved materials are left behind. In this manner, sea water directly materials are left behind. In this manner, sea water 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 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.

海水鹽度如果我們分析海水的鹽度，會發現地區間只有輕微的變化，然而有些小的變化是重要的。
導致海洋的鹽度變化的基本過程有三個，其中之一是通過蒸發的方式即把液態水轉化為水蒸氣來減少海洋中的水分。這樣由于鹽留了下來，所以鹽度增大。
當然，如果這種方式走向極端，將會余下白色的鹽晶體。與蒸發相反的是降水，如降雨，由此水被加入海中，海水被稀釋，從而鹽度降低。
這種情形會發生在大量降雨的地區，或江河入海岸處。因此，鹽度通過蒸發減少水分而上升或通過降水或徑流增加淡水成分而下降。一般來說，在陽光很
強烈的熱帶地區，海水的鹽度略高于世界上其它沒有熱帶那樣多的蒸發的地區。同理，在江河稀釋海水的海岸地帶，海水鹽度略低于其它海區。
第三個可以變更鹽度的過程與海洋中冰的形成和融化有關。海水凍結時，溶于其中的物質被留了下來。這樣，在新形成的海
水冰面的正下方的海水比在冰形成之前有更高的鹽度。當然，當冰融化的時候，會降低周圍水中的鹽度。
在南極洲邊緣的威德爾海中，結冰過程增加低溫海水的鹽度，從而形成了濃度最大的海水。這些大密度的海水下沉，可以在世界海洋的深水域發現。