The sea level has risen about 300 feet since the last ice age ended. The really ancient civilizations are on the continental shelves which ring the continents. Look there my friend and you will be amazed. I would look at the old river mouths for starters.
You speak as if you have secret knowledge.
I quite agree CTP. That’s where all the action has been for most of the last 2 million years or so, during the come-and-go ice ages.