Can CFCs be used to determine anthropogenic CO2?

Abstract

From model simulations of the uptake of CFC‐11, CFC‐12 and anthropogenic CO2, we investigate the method of using CFC‐derived water ages to determine the anthropogenic CO2 accumulation in the ocean. The CFC age method is best suited to water younger than 30 years where CFC water ages are most reliable. For water younger than 30 years, the CFC‐12 and CFC‐11 age method can estimate the global 1980–1990 accumulation of anthropogenic CO2 to within 10% and 22%, respectively. With the exception of the Southern Ocean south of 50°S and the equatorial upwelling areas, these CFC‐derived estimates of the water column inventory of anthropogenic CO2 are within 10% of the simulated values. Our results suggest that the CFC age method provides another way of determining the accumulation of anthropogenic CO2 in the ocean. We applied the CFC age method to observed CFC data to estimate the accumulation of anthropogenic CO2 in the North Pacific (20°N–65°N) between 1980 and 1990. For water younger than 30 years the CFC‐derived estimate of accumulation is 1.1 Gt C. In comparison, the estimate from the simulated CFC distribution is 1.3 Gt C. Our model simulation overestimated the accumulation north of 40°N and underestimated the penetration of anthropogenic CO2 into the subtropical gyre. From the observed CFC data we estimate the anthropogenic CO2 uptake by the North Pacific to be 1.1 Gt C/yr for the 1980s.