deadmau5

hey all i was listening to my uncle talk about a dive he did off the coast of australia not too long ago. He said in an underwater cave below sea level there was a chimney shaped area which had an air pocket at the top of it. as the divers passed through the cave the expelled air rose up the "chimney" and into the pocket. Having dived in this cave many times over the years, and after speaking to many other older divers, my uncle found that the air level in the cave remained constant. Again, the cave is under sea level. Does this have something to do with pressure and the oxygen re-entering the water?