Oceans · a Light

Two seas meet and a barrier lies between them

Surah al-Rahman says He released the two seas, meeting, and between them a barrier they do not overrun. Where a river runs into the sea, oceanographers do find a boundary: fresh water is lighter and rides over a wedge of salt water, and the two keep separate identities for a distance, sometimes with a visible line on the surface where sediment collects. Similar density fronts exist between water masses in the open ocean. What should not be said is that the verse predicted this. These boundaries are not walls, they mix steadily by turbulence and diffusion, and the classical commentators, long before any of it was measured, read the passage as saying that sweet water and salt each keep their character.

Surah al-Rahman 55:19-20

Source · Qur'an 55:19-20