考研優(yōu)美英語(yǔ)作文背誦039

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TheSalinity of Ocean Waters

　　If the salinity of ocean waters is analyzed, it is found to varyonly slightly from place to place. Nevertheless, some of these smallchanges are important. There are three basic processes that cause a change inoceanic salinity.
　　One of these is the subtraction of water from theocean by means of evaporation - conversion of liquid water to water vapor.In this manner the salinity is increased, since the salts stay behind. If thisis carried to the extreme, of course, white crystals of salt would be leftbehind.
　　The opposite of evaporation is precipitation, such as rain, by which water is added to theocean. Here the ocean is being diluted so that the salinity is decreased. Thismay occur in areas of high rainfall or in coastal regions    where rivers flow into the ocean. Thus salinity may be increased by thesubtraction of water by evaporation, or decreased by the addition of fresh waterby precipitation or runoff.
　　Normally, in tropical regions where the sun is verystrong, the ocean salinity is somewhat higher than it is in other parts ofthe world where there is not as much evaporation. Similarly, in coastal regionswhere rivers dilute the sea, salinity is somewhat lower thanin other oceanic areas.
　　A third process by which salinity may be altered isassociated with the formation and melting of sea ice. When sea water isfrozen, the dissolved materials are left behind. In this manner, sea waterdirectly beneath freshly formed sea ice has a higher salinitythan it did before the ice appeared. Of course, when this ice melts, itwill tend to decrease the
　　salinity of the surrounding water. In theWeddell Sea Antarctica, the densest water in the oceans is formed as a resultof this freezing process, which increases the salinity of cold water. Thisheavy water sinks and is found in the deeper portions of the oceans of theworld.
　　全文翻譯：海水鹽度
　　如果我們分析海水的鹽度，會(huì)發(fā)現(xiàn)地區(qū)間只有輕微的變化，然而有些小的變化是重要的。導(dǎo)致海洋的鹽度變化的基本過(guò)程有三個(gè)，其中之一是通過(guò)蒸發(fā)的方式即把液態(tài)水轉(zhuǎn)化為水蒸氣來(lái)減少海洋中的水分。這樣由于鹽留了下來(lái)，所以鹽度增大。當(dāng)然，如果這種方式走向極端，將會(huì)余下白色的鹽晶體。與蒸發(fā)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(huì)發(fā)生在大量降雨的地區(qū)，或江河入海岸處。因此，鹽度通過(guò)蒸發(fā)減少水分而上升或通過(guò)降水或徑流增加淡水成分而下降。一般來(lái)說(shuō)，在陽(yáng)光很強(qiáng)烈的熱帶地區(qū)，海水的鹽度略高于世界上其它沒有熱帶那樣多的蒸發(fā)的地區(qū)。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(qū)。
　　第三個(gè)可以變更鹽度的過(guò)程與海洋中冰的形成和融化有關(guān)。海水凍結(jié)時(shí)，溶于其中的物質(zhì)被留了下來(lái)。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(dāng)然，當(dāng)冰融化的時(shí)候，會(huì)降低周圍水中的鹽度。在南極洲邊緣的威德爾海中，結(jié)冰過(guò)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(fā)現(xiàn)。

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