The Quran on Seas and Rivers

The barriers between the different types of 

water found in nature : a fact mentioned 

in the Quran expounded by science

 

Modern science has discovered that in the places where two different seas , there is a barrier between them. This barrier divides the two seas so that each sea has its own temperature , salinity and density. 
[ Principles of Oceanography, Davis, pp. 92-93 ] 
For example, Mediterranean sea water is warm , saline and less dense compared to the Atlantic Ocean. When Mediterranean sea water enters the Atlantic over the Strait of Gibraltar, several hundred kilometers into the Atlantic moves at a depth of about 1,000 meters, with its temperature , salinity and has less dense . The Mediterranean water stabilizes at this depth [Principles of Oceanography, Davis, p. 93] ( see Figure 1) .

Figure 1: The Mediterranean sea water enters the Atlantic over the Strait of Gibraltar with its own warm, saline and less dense characteristics , because of the barrier that distinguishes them. Temperatures are in degrees Celsius ( ° C ) . ( Marine Geology , Kuenen , p. 43, with a slight improvement . )

Although there are large waves, strong currents and tides in these seas , they do not mix or transgress this barrier .
The Quran says that there is a barrier between two seas that meet and do not exceed . God said :
" He has let free the two seas meet . There is a barrier between them. Exceed not . " (Quran 55:19-20 )
But when the Quran speaks of separation between fresh and salt water , it mentions the existence of an " impassable " in addition to the wall. God says in the Quran:
"It is one that has both types , a soft and palatable open water, and the other salty and bitter. And He has made between them a barrier and imposing. " (Quran 25:53 )
One may ask why the Quran does not mention the partition when speaking about the separation between fresh and salt water, but did not mention when talking about the separation between the two seas ?
Modern science has discovered that in estuaries , where fresh water (sweet) and salt water meet, the situation is somewhat different from what is found in places where two seas meet . It has been discovered that what distinguishes fresh water from salt water in estuaries is a " pycnocline zone with a discontinuity net density separation of the two layers. " [Oceanography, Gross, p. 242.  Also see Introductory Oceanography, Thurman, pp. 300-301] This partition (zone of separation ) has a different salinity from the fresh water and seawater 
[Oceanography, Gross, p. 244, and Introductory Oceanography, Thurman, pp. 300-301] ( see Figure 2) .

Figure 2: Longitudinal section showing salinity (parts per thousand ‰) in an estuary . We can see here the partition (zone of separation) between the fresh and salt water. (Introduction Oceanography , Thurman , p. 301, with a slight improvement )

This information has been discovered recently , using advanced equipment to measure temperature , salinity , density, oxygen solubility , etc. The human eye can not tell the difference between the two seas that meet , rather the two seas appear to us as one homogeneous sea . Likewise, the human eye can not see the division of water in estuaries into three kinds : fresh water , salt water , and the partition (zone of separation ) .