Why do dolphins create air rings and how do they defy buoyancy?

[Isaacsname]

Hello,

I apologize in advance if this is the wrong section, it seemed the most appropriate

Dolphins are able to produce rings of air which seem to counteract buoyancy by rotating ( I'm assuming rotation )

https://www.youtube.com/watch?v=bT-fctr32pE

How and why is this true ?

Thanks

 

[Borek]

They don't counteract buoyancy, they are held in place by a whirlpool - and only for a limited time.

I am moving it to physics, it fits there much better.