Marine CO₂ removal (mCDR) is a promising technology for removing legacy emissions from the atmosphere. Its indirect nature makes it difficult to assess experimentally; instead one relies heavily on simulation. Many past papers have treated the atmosphere as non-responsive to the intervention studied. We show that even under these simplified assumptions, the increase in ocean CO₂ inventory is equal to the equivalent quantity of direct CO₂ removals occurring over time, in a realistic atmosphere.