1.13 established that caves in ocean biomes should be filled with water, preventing awkward air/water interactions. The latest snapshot's new amethyst geode structure often generates in such a way that it intersects the ocean floor, and the result is an awkward air pocket that I doubt to be the intended behavior.

What should happen is they should either generate filled with water, or change the geodes so that the outer shell of tuff and calcite isn't broken allowing this to happen.