> more gravity would create more "pull"? Exactly. There is more mass below the ocean in the areas around where the hole developed and less mass below the hole.

> more gravity would create more "pull"? Exactly. There is more mass below the ocean in the areas around where the hole developed and less mass below the hole. That mass is pulling water from the hole so it became a hole. By the way, less water in the hole and more around it further contribute to making the hole deep because water also have a mass. It doesn't go on forever up to draining the center of the hole dry, there is an equilibrium. Calculating the sea levels could be an unusual physics problem for students.