Anthropogenic CO2 accumulation and uptake rates in the Pacific Ocean based on changes in the C-13/C-12 of dissolved inorganic carbon Global Biogeochemical Cycles

The anthropogenic CO2 accumulation rate for the Pacific Ocean was estimated from the decrease in C-13 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 C-13 change of -8320mdecade(-1) was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic C-13 decreases occurred between 40 degrees S and 60 degrees S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO2 accumulation rate of 0.410.13molCm(-2)yr(-1) (0.820.26PgCyr(-1)) was determined based on observed C-13 changes and is in agreement with previous observation- and model-based estimates. The mean dissolved inorganic carbon DIC13 inventory change of -178 +/- 43 parts per thousand molm(-2)decade(-1) was primarily the result of air-sea CO2 exchange acting on the measured air-sea C-13 disequilibrium of similar to-1.2 +/- 0.1 parts per thousand. Regional differences between the DIC13 inventory change and air-sea (CO2)-C-13 flux yielded net anthropogenic CO2 uptake rates (independent of pCO(2)) that ranged from similar to 0 to 1molm(-2)yr(-1) and basin-wide mean of 1.2 +/- 1.5PgCyr(-1). High rates of surface ocean DIC increase and C-13 decrease observed in the Drake Passage (53 degrees S-60 degrees S) support above average anthropogenic CO2 accumulation since 2005. Observed C-13 changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO2 distribution and illustrate the utility of C-13 as a tracer to unravel the processes controlling the present and future accumulation of anth ropogenic CO2 in the ocean.