My suspicion is that someone has this idea that if we attached a "bubble" to a cable it will pull the cable up and the bubble will expand as it rises and the pressure drops. So all we need to do is keep creating those bubbles and we've a source of energy - which of course is the mythical perpetual motion machine as we'd need to put energy in to get the bubble down to depth in the first place, and losses would mean less out than we put in.
Or perhaps, the suggestion is that the "current" is not constant - if measuring by volume, the air current is lower at the bottom of the system than at the top. But that's because it's measuring the wrong thing - the mass is constant, but as it's compressible it changes volume.
Or perhaps, the suggestion is that the "current" is not constant - if measuring by volume, the air current is lower at the bottom of the system than at the top. But that's because it's measuring the wrong thing - the mass is constant, but as it's compressible it changes volume.