BARRIER BETWEEN SWEET AND SALT WATERS
Consider the following Quranic verses: "He has let free the two bodies Of flowing water, Meeting together: Between them is a Barrier Which they do not transgress." [Al-Quran 55:19
In the Arabic text the word barzakh means a barrier or a partition. This barrier is not a physical partition. The Arabic word maraja literally means 'they both meet and mix with each other'. Early commentators of the Quran were unable to explain the two opposite meanings for the two bodies of water, i.e. they meet and mix, and at the same time, there is a barrier between them. 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] Oceanologists are now in a better position to explain this verse. There is a slanted unseen water barrier between the two seas through which water from one sea passes to the other.
But when the water from one sea enters the other sea, it loses its distinctive characteristic and becomes homogenized with the other water. In a way this barrier serves as a transitional homogenizing area for the two waters. This scientific phenomenon mentioned in the Quran was also confirmed by Dr. William Hay who is a well-known marine scientist and Professor of Geological Sciences at the University of Colorado, U.S.A. The Quran mentions this phenomenon also in the following verse: "And made a separating bar between the two bodies Of flowing water?" [Al-Quran 27:61]
This phenomenon occurs in several places, including the divider between the Mediterranean and the Atlantic Ocean at Gibralter. But when the Quran speaks about the divider between fresh and salt water, it mentions the existence of "a forbidding partition" with the barrier. "It is He Who has Let free the two bodies Of flowing water: One palatable and sweet, And the other salty and bitter; Yet has He Made a barrier between them, And a partition that is forbidden To be passed." [Al-Quran 25:53
Modern science has discovered that in estuaries, where fresh (sweet) and salt-water meet, the situation is somewhat different from that 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 marked density discontinuity separating the two layers." [Oceanography, Gross, p. 242. Also see Introductory Oceanography, Thurman, pp. 300-301.] This partition (zone of separation) has salinity different from both the fresh water and the salt water. [Oceanography, Gross, p. 244 and Introductory Oceanography, Thurman, pp. 300-301.]
This phenomenon occurs in several places, including Egypt, where the river Nile flows into the Mediterranean Sea.
Meeting of the Waters, Manaus, Brazil
This is where the black waters of the Rio Negro meet the brown waters of the Solimoes River.