In Surah Al-Furqan (25:53), the Quran states: "And it is He who has released [simultaneously] the two seas, one fresh and sweet and one salty and bitter, and He placed between them a barrier (barzakh) and prohibiting partition."
This verse describes the meeting of fresh and salt water with a barrier separating them. Modern science has confirmed this phenomenon in estuaries and zones where water masses meet.
Historical context
In the 7th century, it was believed that seas and rivers mixed freely. The concept of a barrier between fresh and salt water was completely unknown. The Quranic description of a separation between these two types of water was therefore a surprising statement for the time.
Scientific confirmation
Modern science has discovered several phenomena that confirm this statement:
- Estuaries: When a river flows into the sea, the less dense fresh water floats above the denser salt water. This stratification creates a transition zone called a halocline where salinity changes abruptly.
- Haloclines: A halocline is a water layer where salinity varies rapidly with depth. It acts as a physical barrier that limits mixing between surface fresh water and deep salt water.
- Meeting zones of seas: In certain straits such as the Strait of Gibraltar, the waters of the Atlantic and the Mediterranean meet but retain their distinct characteristics due to their different density and salinity.
- The salt wedge: In estuaries, salt water penetrates beneath fresh water forming a "salt wedge", creating a clear boundary between the two water masses.
The Quranic term barzakh (برزخ) denotes a barrier or separation. Modern oceanographic science has confirmed the existence of these natural barriers between water masses of different salinity.
The Quran also mentions this phenomenon in Surah Ar-Rahman (55:19-20): "He released the two seas, meeting [side by side]; Between them is a barrier [so] neither of them transgresses."
Scientific significance
The Quranic description of the barrier between fresh and salt water is a remarkable example of early scientific knowledge. Oceanographers only discovered haloclines and estuarine stratification in the 20th century, thus confirming the 7th-century Quranic statement.