Dolphins [...] expel air from their blowholes, generating large, amorphus bubbles that rise quickly to the surface.
Reference
Marten K., Shariff K., Psarakos S. & White D. J. (1996) Ring bubbles of dolphins. Scientific American pp. 82-87.
The animals also produced a column of small air bubbles coming from their blow holes (they were either blown all at once or gradually).
Reference
Delfour F. & Aulagnier S. (1997) Bubbleblow in beluga whales (Delphinapterus leucas): a play activity? Behavioural Processes, 40, 183-186.
The animal emits air from its mouth to yield necklaces of bubbles, which they would pass through or bite.
Reference
Marten K., Shariff K., Psarakos S. & White D. J. (1996) Ring bubbles of dolphins. Scientific American pp. 82-87.
Dolphin shows interest for the air bubbles […] and/or follows them to the water surface.
Reference
Pace D.S. (2000) Fluke-made bubble rings as toys in bottlenose dolphin calves (Tursiops truncatus) Aquatic Mammals, 26.1, 57-64.