This might look playful splashing but it is more likely a territorial display. Guillemots are known to chase one another when contesting burrow territories, perch rocks, and mating attempts. If so provoked, they will dive underwater to continue their pursuit.
The guillemots found on the Project Puffin islands in Maine are numerous enough that they will indeed chase one another from rock to rock or take up with one another in the water.
Photo Courtesy Of: rhamphotheca:
Pigeon Guillemots (Cepphus columba) deuling, Fort Worden State Park, WA, USA
(photo: Andrew Reding)