I just thought i'd input, im relatively new to brewing, but thought i'd share some information from other sources that i've found.
I have a couple aquariums, and always thought that putting bubbles of air into the water would aid in the oxygen level in the water, but come to find out its a VERY minimal effect in comparison to circulating the top surface of liquid (in our case, beer).
The idea is that the surface area of a group of bubbles is very little when compared to the top surface area of an aquarium, or again, in our case, a fermenter. The oxygen absorption, thus, takes place mostly on the top surface. So hopefully this can shine some light on the most effective methods of oxygenation.