A number of workers have presented calculation attempting to show the anthropogenic CO2 increase in the ocean. These workers back-calculate the CO2 concentration of a water parcel to when it was at the sea surface by using well-known ratios to correct for chemical changes induced by biological decomposition. Because of the potential significance of these CO2 back-calculations, their limitations are examined here. In the Antarctic Intermediate Water, which has served as a primary testing ground for these backcalculation models, mixing is seen to significantly alter chemical concentrations. However, previously used mixing corrections are shown to have little effect on an analogous back-calculation of preformed nitrate. Additionally, the results of the CO2 back-calculations are probably too high for the water mass in question. Thus the ability of these methods to provide reliable estimates of the oceanic CO2 increase is in doubt.