Comparison of methods to determine the anthropogenic CO2 invasion into the Atlantic Ocean

A comparison of different methods for estimating the anthropogenic CO2 burden in the Atlantic Ocean is performed using referenced, high quality total dissolved inorganic carbon (DIC) data. The dataset is from two cruises through the center of the basin between 62 degrees N and 43 degrees S in 1991 and 1993. The specific anthropogenic input is determined utilizing empirical procedures as described in Gruber et al. (1996) and Chen and Millero (1979) to correct for remineralization and to estimate preanthropogenic endmembers. These estimates are compared with output of the Princeton ocean biogeochemical model and the NCAR ocean model. The results show that the specific inventories of anthropogenic carbon agree to within 20% but with different storage and uptake patterns. The empirical estimates differ because of assumptions about mixing and winter outcrop endmembers. The same remineralization quotients (Redfield ratios) were used for each method. Varying these constants within the range of literature values causes changes in specific inventories of similar magnitude as the differences observed with different methodologies. Comparison of anthropogenic CO2 uptake and chlorofluorocarbon ages suggests that the anthropogenic CO2 penetration in the North Atlantic is too shallow following the procedure according to Gruber et al. (1996), and too deep using those of Chen and Millero (1979). The results support these previous observations in that the uptake of CO2 in the North Atlantic is disproportionate to its surface area. This is caused by a combination of deep water formation and deep winter mixed layers.