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I totally disagree that this is a question for an expert. Any self 
respecting diver should be able to calculate pressure and volume
relationships and understand archimedes principle. I also think that
the question was wrong. The explanation follows:-

To make a diver neutrally buoyant he requires a volume of air in his
BC. Assuming that the suit is incompressible and has no air in it all
the diver has to do is maintain the same volume ( V ) of air in his BC
to be neutrally buoyant at any depth. ( Archimedes paraphrased- a body
is neutrally buoyant if it displaces exactly it's own mass of water.)

Lets call the 'amount' of air the equivalent volume at 1 atmosphere 
pressure. So amount of air = absolute pressure * volume.

Okay, 33fsw at sea level dives an absolute pressure of 1.99 atm.
      23fsw at 10,000 ft give 0.5 atm ambient + 0.69 atm water = 1.19 atm

Since the volume of the BC is the same in both cases the absolute pressure
indicates that very obviously the dive at sea level requires more air 
( in terms of mass, or equivalent volume of air at sea level).

If the question been a 23ft dive at sea level and a 33ft dive at 10,000 ft
it would have been more interesting:-

33fsw at 10,000 ft gives an absolute pressure of 0.5atm +0.99atm = 1.49atm 
23fsw at sea level gives 1.69 atm.

This shows the slightly surprising result that the shallower dive at sea
level requires more air from your tank to fill the BC than the deeper
dive at altitude. 

If american divers used the metric system for their air calculations they
would find this sort of stuff a lot easier. ( My opinion only).

Andy.   

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