But it's taking carbon out of the ocean and releasing it into the atmosphere. The issue becomes, how long does it take for the released atmospheric CO2 to be reabeorbed back into he ocean? Does it do more harm in the atmosphere or in the ocean?

Right now we're taking carbon out of the ground and putting it in the atmosphere.

The ocean presently has a lot of extra carbon, which it absorbed from the atmosphere. So this is an indirect way of taking carbon out of the atmosphere and then putting it back...a closed loop. If we did this for all our hydrocarbon fuel we'd be carbon-neutral.