The dolphin directs the ring of bubbles downwards

- how do you direct bubbles to go DOWN?

The ring seems to act like a lens, refracting the image inside its area slightly

- how do you make a lens out of water in water without a container and with a different refractive index to water?

The bubbles at the lower portion of the circle gradually disappear

- where do the bubbles go?

The bubbles re-appear at the lower portion of the circle

- where do new bubbles come from if the dolphin didn't blow them?

Note how the movement of the ring follows the direction of the dolphin's snout, although it cannot be "blowing" with it's mouth because it's mouth is closed and it would blow air (it is a mammal) which would be visible as more bubbles in a "jet".

- what force is the dolphin using to direct the "lens"/bubble ring?

The two still pics below are my attempts to make clear what I see happening on these films.

Here is what I think is happening. I think the dolphin can use its sonar to compress a two close standing waves of ultrasound that trap and squeeze a disc shaped layer of water immediately in front of it's snout.

I think it can vary the distance of this and the diameter, and that it only uses the initial ring of bubbles as a guideline to set up the disc (it needs to hear the coordinates of a disc to range-find for its standing wave trick). And I think the pressure between the discs forces some of the air in the water out of aqueous solution and that is why the margin of bubbles comes and goes.

If I am only half-way right then this indicates that the dolphin has a control over sonar that exceeds anything humans can do - or are likely to be able to do for some decades.