Calculating the oceanic CO₂ increase: A need for caution

A number of workers have presented calculations attempting to show the anthropogenic CO 2 increase in the ocean. These workers back‐calculate the CO 2 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 CO 2 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 CO 2 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 CO 2 increase is in doubt.