New underwater caves

One of the caves system that Minecraft desperately has to fix is the underwater caves. Having to use water breathing or respiration in a cave that barely has any new ways of improving the games mechanic or having to explore is just kind of a waste.

A benefit for a new underwater cave system is introducing new blocks or a brand new ore that is found exclusively underwater in the cave. 

This new ore which would be called aquamarine could be a benefit for using tools or items underwater since regularly underwater cave if someone even uses it would have a hard time mining because of how pickaxes work in water.