Minecraft v1.15.2
Forge v31.2.19
Better Caves v1.0

Massive air bubbles seem to form in oceans, extending underneath the land. I'm using a bop world type, if that affects anything.

Are you using quark? Looks like one of those sideways ravines to me.

Yes, Quark is being used. I didn't realize Quark added that. But it seems to extend into the water.

Yeah, it's a feature of theirs and I'm pretty sure that is what this is. I would try posting this on their issue tracker to see if they can help you out.

Thanks, I'll give it a try.