Distinct water masses and the salinity of the seas

Surah Fatir Verse 12 2026-09-03 23:00:56

Quranic verses

وَمَا يَسْتَوِي الْبَحْرَانِ هَذَا عَذْبٌ فُرَاتٌ سَائِغٌ شَرَابُهُ وَهَذَا مِلْحٌ أُجَاجٌ وَمِن كُلٍّ تَأْكُلُونَ لَحْمًا طَرِيًّا وَتَسْتَخْرِجُونَ حِلْيَةً تَلْبَسُونَهَا وَتَرَى الْفُلْكَ فِيهِ مَوَاخِرَ لِتَبْتَغُوا مِن فَضْلِهِ وَلَعَلَّكُمْ تَشْكُرُونَ

And not alike are the two seas. One is fresh and sweet, palatable for drinking, and one is salty and bitter. And from each you eat tender meat and extract ornaments which you wear, and you see the ships plowing through [them] that you might seek of His bounty; and perhaps you will be grateful.

Surah Fatir (35:12)

وَهُوَ الَّذِي مَرَجَ الْبَحْرَيْنِ هَذَا عَذْبٌ فُرَاتٌ وَهَذَا مِلْحٌ أُجَاجٌ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَحِجْرًا مَّحْجُورًا

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 and prohibiting partition.

Surah Al-Furqan (25:53)

In Surah Fatir (35:12), the Quran declares: "And not alike are the two seas. One is fresh and sweet, palatable for drinking, and one is salty and bitter" (وَمَا يَسْتَوِي الْبَحْرَانِ هَذَا عَذْبٌ فُرَاتٌ سَائِغٌ شَرَابُهُ وَهَذَا مِلْحٌ أُجَاجٌ).

This verse clearly distinguishes fresh waters from salty waters, a reality that modern oceanography has precisely characterized.

The salinity of the oceans

The average salinity of seawater is about 35 parts per thousand (35 g of salt per liter of water). This salinity varies by region: Red Sea (~40 ppt), Atlantic Ocean (~35-37 ppt), Pacific Ocean (~34-35 ppt), Baltic Sea (~7-8 ppt).

Distinct water masses

Modern oceanography has discovered that oceans are composed of distinct water masses, each with its own temperature, salinity, and density. These water masses do not mix easily: Atlantic and Mediterranean waters have different characteristics, and at the Strait of Gibraltar, the more saline and dense Mediterranean waters dive beneath the Atlantic waters.

Verse 25:53 also mentions: "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 and prohibiting partition" (وَهُوَ الَّذِي مَرَجَ الْبَحْرَيْنِ هَذَا عَذْبٌ فُرَاتٌ وَهَذَا مِلْحٌ أُجَاجٌ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَحِجْرًا مَّحْجُورًا).

The term barzakh (بَرْزَخًا) designates a barrier or intermediate zone. Oceanography has confirmed the existence of such transition zones where water masses meet without completely mixing.

This knowledge of distinct water masses was only scientifically established from the HMS Challenger expedition (1872-1876), the first major oceanographic expedition, and deepened in the 20th century.

Scientific findings

Average salinity of seawater: ~35 ppt
Oceans are composed of distinct water masses (temperature, salinity, density)
Water masses do not mix easily (barzakh / transition zone)
TEOS-10 (2010): modern system for measuring absolute salinity
HMS Challenger expedition (1872-1876): foundation of modern oceanography

Scientific references

Physical Significance of the Barrier Between Two Seas — Quranica (Journal of Quranic Studies, 2020)
Quran on Barrier Between Seas — The Last Dialogue (thelastdialogue.org, 2019)
Seawater salinity measurement — Thermal Engineering (thermal-engineering.org, 2020)
The Challenger Expedition — National Oceanography Centre (noc.ac.uk, 2019)