This was in the news several years ago. If they haven't got evidence yet, they never will get it---because it isn't there. No city, no pyramids, no Atlantis.
Some say as much as 500ft.
Regardless, block off the Carribean and it'll dry up. The unsuspecting builders built it on the shoreline of the very much lowered Gulf Of Mexico coast. Incidentally, I also believe the same thing happened in the Mediterranean...may have been sectioned into 2-3 parts.