SEA WATER 217 



dissolved in the water may vary from time to time and place 

 to place for various reasons. The open ocean water, how- 

 ever, varies in its salinity within very small limits being 

 almost always between 34 and 36 parts of salt to a thousand 

 parts of water by weight. It is quite natural that in the 

 neighbourhood of land the amount of dissolved salt is lower 

 than in the open ocean owing to the fresh water which 

 flows off the land diluting it. 



In the Baltic Sea, for instance, the salinity of the water 

 is very low, being always below twenty-nine parts per 

 thousand. As we get down to the mouth of the Baltic, 

 however, where it joins the North Sea in the Skager Rack 

 we notice a considerable rise in the salinity due to the 

 mingling of more saline waters coming from the North Sea 

 itself and from water carried round by the drift of the Gulf 

 Stream which penetrates the North Sea round the north 

 of Scotland. Owing to its lessened salinity the stream of 

 Baltic water is quite recognizable as it flows up past the 

 coast of Norway. 



On the other hand the salinity of sea water may be 

 considerably higher than that of the open ocean owing to 

 constant evaporation of the water from the surface and a 

 consequent concentration of the salts left behind. Such 

 conditions are to be found in the Red Sea, where the highest 

 salinities in the world, for open waters, occur, viz. forty 

 parts per thousand. Here, under the fearful heat of the 

 sun, water is constantly evaporating at the sea surface and 

 there are no rivers flowing down from the land with fresh 

 water to dilute the sea once more. The eastern basin 

 of the Mediterranean is also very salt compared with the 

 open waters of the Atlantic. 



(In the case of the " Dead Sea " river water has been 

 pouring down for thousands of years into a comparatively 

 small lake in which constant evaporation is taking place. 



