Although there
are large waves, strong currents, and tides in these seas, they
do not mix or transgress this barrier.
The Holy Qur'an mentioned that there is a barrier between two
seas that meet and that they do not transgress. God said:
{He has let free the two seas meeting
to gather. There is a barrier between them. They do not transgress.}
(Qur'an 55:19-20)
But when the
Qur'an speaks about the divider between fresh and salt water,
it mentions the existence of "a forbidding partition"
with the barrier.
God said in the Qur'an:
{He is
the one who has let free the two bodies of flowing water, one
sweet and palatable, and the other salty and bitter. And He
has made between them a barrier and a forbidding partition.}
(Qur'an 25:53)
On may ask, why did the Qur'an mention
the partition when speaking about the divider between fresh
and salt water, but did not mention it when speaking about the
divider between the two seas?
Modern science has discovered that in estuaries, where fresh
(sweet) and salt water meet, the situation is somewhat different
from what is 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
p. 242)
This partition (zone of separation) has
a different salinity from the fresh water and from the salt
water (Oceanography p. 244 and Introductory Oceanography pp.
300-301)
This information
has been discovered only recently using advanced equipment to
measure temperature, salinity, density, oxygen dissolubility,
etc. The human eye cannot see the difference between the two
seas that meet, rather the two seas appear to us as one homogeneous
sea. Likewise the human eye cannot see the division of water
in estuaries into the three kinds: the fresh water, the salt
water, the partition (zone of separation).