Anthropogenic CO 2 accumulation and uptake rates in the Pacific Ocean based on changes in the 13 C/ 12 C of dissolved inorganic carbon

The anthropogenic CO 2 accumulation rate for the Pacific Ocean was estimated from the decrease in δ 13 C of the dissolved inorganic carbon measured on six World Ocean Circulation Experiment cruises during the 1990s and repeated during Climate Variability and Predictability in the 2000s. A mean depth‐integrated anthropogenic δ 13 C change of −83 ± 20‰ m decade −1 was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic δ 13 C decreases occurred between 40°S and 60°S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO 2 accumulation rate of 0.41 ± 0.13 mol C m −2  yr −1 (0.82 ± 0.26 Pg C yr −1 ) was determined based on observed δ 13 C changes and is in agreement with previous observation‐ and model‐based estimates. The mean dissolved inorganic carbon DIC 13 inventory change of −178 ± 43‰ mol m −2  decade −1 was primarily the result of air‐sea CO 2 exchange acting on the measured air‐sea δ 13 C disequilibrium of ~ −1.2 ± 0.1‰. Regional differences between the DIC 13 inventory change and air‐sea 13 CO 2 flux yielded net anthropogenic CO 2 uptake rates (independent of ΔpCO 2 ) that ranged from ~0 to 1 mol m −2  yr −1 and basin‐wide mean of 1.2 ± 1.5 Pg C yr −1 . High rates of surface ocean DIC increase and δ 13 C decrease observed in the Drake Passage (53°S–60°S) support above average anthropogenic CO 2 accumulation since 2005. Observed δ 13 C changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO 2 distribution and illustrate the utility of δ 13 C as a tracer to unravel the processes controlling the present and future accumulation of anthropogenic CO 2 in the ocean.