Can we start a Bioshock 2 section ?

I had an issue with performance in Bioshock 2.. the game was having a terrible frame rate even though I had a card that was higher than their recommended level. The frame rate remained low even after I lowered all the graphics settings to their lowest. Finally after lot of trial and error and some help from some gaming forums, I found the culprit. It was the Ambient Occlusion.