Anthropogenic CO2 accumulation rates in the North Atlantic Ocean from changes in the C/C of dissolved inorganic carbon

[1] The anthropogenic CO2 accumulation rate for the North Atlantic Ocean was estimated on the basis of the decrease in the dC of the dissolved inorganic carbon measured between cruises in 1981 (Transient Tracers in the North Atlantic), 1993 (OACES) and 2003 (Repeat Hydrography). A mean depth-integrated dC change of 15.0 ± 3.8% m yr 1 was estimated by applying a multiple linear regression approach to determine the anthropogenic dC decrease at 22 stations where dC depth profiles were compared. The largest and deepest anthropogenic dC decreases occurred in the subpolar ocean and, in contrast, the smallest and shallowest decreases occurred in the tropical ocean. A mean anthropogenic CO2 accumulation rate of 0.63 ± 0.16 mol C m 2 yr 1 (0.32 ± 0.08 Pg C yr ) in the North Atlantic Ocean over the last 20 years was determined from the mean depth-integrated dC change and a ratio of anthropogenic dC to DIC change of 0.024% (mmol kg ) . Only half of the accumulated anthropogenic CO2 in the North Atlantic during the last 20 years was the result of air-sea CO2 uptake, based on a comparison of the air-sea CO2 flux to the DIC 13 inventory change, with the other half likely a result of northward advective transport.