An upgraded carbon-based method to estimate the anthropogenic fraction of dissolved CO2 in the Atlantic Ocean

45 páginas, 3 tablas, 7 figuras.-- This work is distributed under the Creative Commons Attribution 3.0 LicenseAn upgrade of classical methods to calculate the anthropogenic carbon (Cant) signal based on estimates of the preformed dissolved inorganic carbon (CT) is proposed and applied to modern Atlantic sections. The main progress has been the use of subsurface layer data (100–200 m) to reconstruct water mass formation conditions and obtain better estimates of preformed properties. This practice also eliminates the need for arbitrary zero-Cant references that are usually based on properties independent of the carbon system, like the CFC content. The long-term variability of preformed total alkalinity (AT) has been considered and the temporal variability of the air-sea CO2 disequilibrium (ΔCdis) included in the formulation. The change of ΔCdis with time has shown to have non-negligible biases on Cant estimates, producing a 4 μmol kg average decrease. The proposed φCT method produces substantial differences in the Cant inventories of the Southern Ocean and Nordic Seas (~18% of the total inventory for the Atlantic) compared with recent Cant inventories. The overall calculated Atlantic Cant inventory referenced to 1994 is 55±13 Pg C, which reconciles the estimates obtained from classical CT-based Cant calculation methods, like the ΔC*, and newly introduced approaches like the TrOCA or the TTD methods.This study was developed and funded by the European Commission within the 6th Framework Programme (EU FP6 CARBOOCEAN Integrated Project, Contract no. 511176), Ministerio de Educacion y Ciencia (CTM2006-27116-E/MAR), Xunta de Galicia (PGIDIT05PXIC40203PM), Accion Integrada Hispano-Francesa (HF2006-0094) and the French research project OVIDE. M. Vazquez-Rodriguez is funded by Consejo Superior de Investigaciones Cientificas (CSIC) I3P predoctoral grant program I3P-BPD2005. Funding for Richard G. J. Bellerby was provided from grant no. 511176 (GOCE).Peer reviewe