Trends of anthropogenic CO2 storage in North Atlantic water masses

• Published in: Biogeosciences
• Main Authors: Perez, F. F, Vazquez-rodriguez, M., Mercier, Herle, Velo, A., Lherminier, Pascale, Rios, A. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Gesellschaft Mbh 2010
• Subjects: Irminger Basin; Irminger Sea; Iceland; North Atlantic Deep Water; North Atlantic; North Atlantic oscillation
• Online Access: https://archimer.ifremer.fr/doc/00006/11706/8362.pdf; https://doi.org/10.5194/bg-7-1789-2010; https://archimer.ifremer.fr/doc/00006/11706/

A high-quality inorganic carbon system database, spanning over three decades (1981-2006) and comprising of 13 cruises, has allowed the applying of the phi C degrees(T) method and coming up with estimates of the anthropogenic CO2 (C-ant) stored in the main water masses of the North Atlantic. In the studied region, strong convective processes convey surface properties, like C-ant, into deeper ocean layers and grants this region an added oceanographic interest from the point of view of air-sea CO2 exchanges. Generally, a tendency for decreasing C-ant storage rates towards the deep layers has been observed. In the Iberian Basin, the North Atlantic Deep Water has low C-ant concentrations and negligible storage rates, while the North Atlantic Central Water in the upper layers shows the largest C-ant values and the largest annual increase of its average concentration (1.13 +/- 0.14 mu mol kg(-1) yr(-1)). This unmatched rate of change in the C-ant concentration of the warm upper limb of the Meridional Overturning Circulation decreases towards the Irminger basin (0.68 +/- 0.06 mu mol kg(-1) yr(-1)) due to the lowering of the buffering capacity. The mid and deep waters in the Irminger Sea show rather similar C-ant concentration rates of increase (between 0.33 and 0.45 mu mol kg(-1) yr(-1)), whereas in the Iceland basin these layers seem to have been less affected by C-ant. Overall, the C-ant storage rates in the North Atlantic subpolar gyre during the first half of the 1990s, when a high North Atlantic Oscillation (NAO) phase was dominant, are similar to 48% higher than during the 1997-2006 low NAO phase that followed. This result suggests that a net decrease in the strength of the North Atlantic sink of atmospheric CO2 has taken place during the present decade. The changes in deep-water ventilation are the main driving processes causing this weakening of the North Atlantic CO2 sink.