1989, there is a moon pool on the drilling platform in the abyss. It seems that later, all the other cabins were flooded. Why is there a moon pool connected to the sea?

Because all doors connected to the moon pool are sealed, when you enter other cabins, you must close the door connected to the moon pool before opening the next door. The principle is very simple, pneumatic principle. For example, if you put a basin upside down in water, even if the water level is very low, the water in the basin will not be full and air will still be in it. Although the moon pool in the movie is empty, it can bear the same pressure as the sea water at the same depth. Do you understand?