"“The study did suggest the possibility of pockets of water,” Dr. Navon said. “If you want to relate this to the Bible, it would fit nicely with the description of the Flood of
Noah in which the flood resulted from rain and water from below.”
So, you should not confuse the two areas of water beneath the surface. There is water below the surface and not in the mantel.
Now, the "sky" water or firmament with on one side water is interesting. Because, there are those who believe the way Genesis is written that the sun was blocked by water in the sky. And, this is why people lived to be very old prior to the flood. So, when the rains began, water came up from the water pockets in the earth's crust along with a huge downpour of water from the heavens or the firmament.
Now, listen to the article I provided.