Great Internal Cave

The Great Internal Cave
The largest of any other pockets, this place is home to the D and its many descendants. "The largest of the caves."

Current Atmospheric Composition: 53% nitrogen, 20% oxygen, 2% argon, 21% carbon dioxide, and 4.1% other gases. Trace amounts of, methane, water vapor, and neon are some of the other gases that make up the remaining 4.1%.

With a decent amount of gas exchangers, the composition of gasses in both water and in the atmosphere of the Great Internal Cave is slowly changing. Slowly enough that it has not killed off a significant amount of the population.