S7
Two seas and a barrier
55:19–20 and 25:53 describe two bodies of water, "one fresh and sweet and one salty and bitter", released side by side with "a barrier" between them.
مَرَجَ ٱلْبَحْرَيْنِ يَلْتَقِيَانِ١٩ بَيْنَهُمَا بَرْزَخٌ لَّا يَبْغِيَانِ٢٠
Transliteration: maraja l-baḥrayni yaltaqiyāni · baynahumā barzakhun lā yabghiyāni
He released the two seas, meeting [side by side]; Between them is a barrier [so] neither of them transgresses.
۞ وَهُوَ ٱلَّذِى مَرَجَ ٱلْبَحْرَيْنِ هَٰذَا عَذْبٌ فُرَاتٌ وَهَٰذَا مِلْحٌ أُجَاجٌ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَحِجْرًا مَّحْجُورًا٥٣
Transliteration: wahuwa alladhī maraja l-baḥrayni hādhā ʿadhbun furātun wahādhā mil'ḥun ujājun wajaʿala baynahumā barzakhan waḥij'ran maḥjūran
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.
Translation: Saheeh International
"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" (25:53), Sura al-Furqān, Meccan.
Key words
Maraja ("released"): let loose, let flow freely. Baḥr ("sea"): a large body of water; Ibn Kathir's reading below shows it can cover rivers too. Barzakh ("barrier"): something that stands between two things. Ḥijran maḥjūran ("prohibiting partition"): a barrier that forbids passage.
What the verses say
Two waters meet; something between them keeps each from overrunning the other. 25:53 says plainly that one is fresh and one is salt.
Classical tafsir
Ibn Kathir on 55:19–20. Maraja means "let them loose" (citing Ibn ʿAbbas). "The two seas are the fresh and salty waters, the former coming from running rivers." On the barrier: God placed "a barrier of land between these two types of waters", and he quotes Ibn Zayd: God "prevents them from meeting by the dividing barrier He placed between them".
Ibn Kathir on 25:53. The sweet water is "like that in rivers, springs and wells"; "nowhere in creation is there a sea which is fresh and sweet". The salt sea is "salty, bitter and not easy to swallow", like the Red Sea, the Mediterranean and the Indian Ocean. The barzakh is "a partition, which is dry land", and the "prohibiting partition" is "a barrier, to prevent one of them from reaching the other". He cites Ibn Jurayj and Ibn Jarir al-Tabari for the sweet-water meaning, calling it "the meaning without a doubt".
Al-Jalālayn on 55:19. "He has loosed the two waters the sweet and the salty; and so they meet in the perception of the eye."
Al-Jalālayn on 25:53. "merged the two seas letting them flow one adjacent to the other"; "He set between the two an isthmus"; "a forbidding ban a shield that prevents the two from becoming mixed".
Where they differ. Ibn Kathir's barrier is physical land: rivers and seas are separated by the ground between them. Al-Jalālayn's is less specific: the two waters "meet in the perception of the eye", and a "shield… prevents the two from becoming mixed". Neither describes a boundary inside the sea, and neither mentions Gibraltar.
How it works
Text version
At the Strait of Gibraltar, lighter Atlantic water flows into the Mediterranean on top. Saltier, denser Mediterranean water (38 g/kg, 13 °C) flows out beneath it at about 120 m depth, spills over the sill and sinks to about 1,100 m, at about a million cubic metres a second. Tides over the sill make internal waves, and at the boundary the two waters mix: "the two seas never mix" is not true.
Each point is tied to the verses' words "released… meeting", "fresh and sweet… salty and bitter" and "barrier".
- Where fresh meets salt. Established In an estuary, where a river meets the sea, fresh water "floats on top of the heavier seawater" because it is less dense (NOAA). This is the nearest physical picture of 25:53: "one fresh and sweet and one salty and bitter", side by side.
- How sharp the boundary is depends on tides and river flow. Established NOAA classifies estuaries by how much they mix:
- "Salt-wedge estuaries occur when a rapidly flowing river discharges into the ocean where tidal currents are weak": a sharp boundary, fresh above, a wedge of salt below.
- In partially mixed estuaries "saltwater and freshwater mix at all depths", but the lower layers stay saltier.
- In well-mixed estuaries, "Strong tidal currents eliminate the vertical layering". So a "barrier" of density can be sharp, gradual or absent.
- Two salt seas: Gibraltar. Established Mediterranean water leaving through the Strait of Gibraltar has a salinity of "38 g/kg" and a temperature of "13 °C", "extremely high compared with any other waters in that depth range". It exits at about 120 m depth and sinks to an equilibrium depth of about 1,100 m, at a rate of about 1 Sverdrup (a million cubic metres per second) (Wikipedia, "Mediterranean outflow").
- But it does mix. Established At Gibraltar, tides flowing over the Camarinal Sill create "an internal bore", which breaks into internal waves that drive strong mixing; the outflow becomes "less saline due to mixing" as it moves west. Lenses of Mediterranean water called meddies, with radii of 10–50 km (about 20–100 km across) and 500–1,000 m thick, carry its salt far into the Atlantic; "between 15 and 20 meddies are formed" each year (Wikipedia).
- The viral video. Established A widely shared photo said to show "two oceans meeting but not mixing" in the Gulf of Alaska shows, according to Lead Stories, "another river plume taken during a research cruise in the Gulf of Alaska" (photo by Kent Smith, 2010). Ocean Networks Canada, quoted there, describes a similar plume as "a puddle of light water (formed by mixing fresh Fraser water with salt water)".
Points of awe
Where a river meets the sea, its fresh water can ride over the salt water in a distinct layer (NOAA).
About a million cubic metres of Mediterranean water pour into the Atlantic every second, beneath the incoming Atlantic water (Wikipedia).
Reflection
Two waters meet. One is sweet, one bitter. They are "released", free to flow, and still something keeps each from overrunning the other: "Between them is a barrier [so] neither of them transgresses" (55:20).
The commentators saw the plainest form of this. Rivers run sweet; seas are salt; the land stands between them. Al-Jalālayn adds that where they touch, they "meet in the perception of the eye" yet stay distinct. Today we can watch a river's fresh water ride over the sea before it slowly blends.
Sura al-Raḥmān does not offer this as a puzzle. It offers it as a favour, and after each sign asks which of the Lord's favours we would deny. Rivers that stay sweet long enough to water fields, and seas that stay salt, are both gifts.
There is a picture here for human life, offered as reflection. People of very different kinds live side by side. Each can keep its own nature without overrunning the other, within an order neither of them made. The verse calls that restraint a barrier; it might also be called justice.
Questions readers ask next
Did classical scholars mean an invisible barrier in the sea?
No. Ibn Kathir explains the barrier as land between rivers and sea; al-Jalālayn as a "shield" keeping them from mixing. Modern estuary science is described separately.
Is the barrier "proof" of modern oceanography?
No. The page treats it as a sign to notice, not a prediction, and the popular "never mix" claim is false (see the honest notes).
What is an estuary?
The place where a river meets the sea, where fresh and salt water meet and, depending on tides and river flow, layer or mix (NOAA).
What is happening at Gibraltar?
Salty, warm Mediterranean water flows out under the Atlantic water flowing in, then sinks to about 1,100 m; tides mix it strongly at the strait (Wikipedia).
What does "neither of them transgresses" mean?
That neither overruns the other. For Ibn Kathir, land keeps rivers and seas apart; in estuaries, density keeps fresh water above salt water for a while.
Sources
- Saheeh International — 55:19–20, 25:53.
- Ibn Kathir, Tafsir (abridged English), and Tafsīr al-Jalālayn (English), on 55:19–20, https://surahquran.com/tafsir-english-aya-19-sora-55.html, and on 25:53, https://surahquran.com/tafsir-english-aya-53-sora-25.html.
- NOAA, Estuaries Tutorial, "Classifying Estuaries: By Water Circulation", https://oceanservice.noaa.gov/education/tutorial_estuaries/est05_circulation.html.
- "Mediterranean outflow", Wikipedia, https://en.wikipedia.org/wiki/Mediterranean_outflow.
- Sarah Thompson, "Fact Check: This Is NOT A Picture Of Two Oceans Meeting But Not Mixing", Lead Stories (29 January 2021), https://leadstories.com/hoax-alert/2021/01/fact-check-this-is-not-a-picture-of-two-oceans-meeting-but-not-mixing.html.
- "The Quran on Seas and Rivers", islam-guide.com, on IslamReligion.com, https://www.islamreligion.com/articles/214/ — the popular modern claim.
- Mediterranean outflow (Wikipedia)
- Bryden et al.; Science Advances (2018)
- Al-Ṭabarī and Ibn Kathīr on 55:19–20