There is a strange science involved in the mixing of waters. The phenomenon is different when two seas meet and different when fresh and salty water meet, and Quran has explained it all in clear details. Amazingly, after about 1400 years, the modern science has come up with all theories which certify the correctness of Quranic verses.
Modern Science has discovered that in the places where two different seas meet, 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 Atlantic Ocean water. When Mediterranean Sea water enters the Atlantic over the Gibraltar sill, it moves several hundred kilometers into the Atlantic at a depth of about 1,000 meters with its own warm, saline and less dense characteristics. The Mediterranean water stabilizes at this depth. [Principles of Oceanography p. 93]
The Mediterranean Sea water as it enters the Atlantic over the Gibraltar sill with its own warm, saline and less dense characteristics, because of the barrier that distinguishes between them. Temperatures are in degrees Celsius (C). Even in depths (indicated here by darker colors) up to 1,400 meters and at distances ranging from a minus -100 to +2,500 meters, we find that both bodies of water maintain their individual temperatures and salinity. Although there are large waves, strong currents, and tides in these seas, they do not mix or transgress this barrier.
The Holy Quran mentioned that there is a barrier between two seas that meet and that they do not transgress. God said:
He has granted freedom to the two great seas to meet
[Noble Quran 55:19]
Yet there is a barrier in between which they cannot delete
[Noble Quran 55:20]
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