The international geography . greater depththan in the tropics, and it is thinnest of all in the south-eastern parts ofthe three oceans. Circulation of Enclosed Seas.—The whole mass of water in theocean is believed to be in continual though very slow motion, becausethere is no abrupt change of temperature anywhere between massesof water at the same depth and not separated by a ridge. But inenclosed seas, which are cut off from the ocean by a barrier, the tem-perature corresponds to that of the ocean only from the surface to thed^pth of the barrier ; below that the water retains the same temper
The international geography . greater depththan in the tropics, and it is thinnest of all in the south-eastern parts ofthe three oceans. Circulation of Enclosed Seas.—The whole mass of water in theocean is believed to be in continual though very slow motion, becausethere is no abrupt change of temperature anywhere between massesof water at the same depth and not separated by a ridge. But inenclosed seas, which are cut off from the ocean by a barrier, the tem-perature corresponds to that of the ocean only from the surface to thed^pth of the barrier ; below that the water retains the same temperatureunchanged to the bottom. Thus the Mediterranean has a uniformtemperature of 55° from 190 fathoms, the depth of the Strait of Gib-raltar, to the bottom in 2,400 fathoms (the Atlantic has a temperatureof f 5° at the latter depth) ; and the Red Sea has a temperature of yofrom 200 fathoms, the depth of the Strait of Bab-el-Mandeb, to thebottom in 1,200 fathoms. Enclosed seas are not as a rule stagnant, but The Oceans 67. Fig 39.—Diagram showing temperature 0/ Red Sea. their waters circulate on account of their differences in salinity. Thusthe water of the Red Sea and the Mediterranean is much Salter anddenser than that of the ocean, so that when the level of the enclosed sea isreduced by evaporation the comparatively light ocean water flows in asa surface current, while thedense warm water sets out-wards as a return current alongthe bottom. In the shallowBaltic and the deep Black Sea,on the contrary, the numerousrivers which flow in make thewater so fresh that it overflowsas a surface current, whilethe dense ocean-water flows in as an under-current. The Baltic is, how-ever, very variable in its circulation on account of the action of wind, andthe Black Sea is so deep that its lower waters are absolutely stagnant andputrid, unfit for the support of animal life of any kind. In shallow partially-enclosed seas, such as the North Sea, tidal currents play a notable part inthe
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectgeography, bookyear19
