Atlantic Ocean CO 2 uptake reduced by weakening of the meridional overturning circulation

• Published in: Nature Geoscience
• Main Authors: Perez, FF, Mercier, H, Vazquez-Rodriguez, M, Lherminier, P, Velo, A, Pardo, PC, Roson, G, Rios, AF
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2013
• Subjects: Earth Sciences; Atmospheric Sciences; Climate Change Processes; North Atlantic
• Online Access: https://doi.org/10.1038/NGEO1680; http://ecite.utas.edu.au/103035

Uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006. This reduction in carbon dioxide uptake was related to warming at the sea surface, whichaccording to model simulationscoincided with a reduction in the Atlantic meridional overturning circulation. The extent to which the slowdown of this circulation systemwhich transports warm surface waters to the northern high latitudes, and cool deep waters southcontributed to the reduction in carbon uptake has remained uncertain. Here, we use data on the oceanic transport of volume, heat and carbon dioxide to track carbon dioxide uptake in the subtropical and subpolar regions of the North Atlantic Ocean over the past two decades. We separate anthropogenic carbon from natural carbon by assuming that the latter corresponds to a pre-industrial atmosphere, whereas the remaining is anthropogenic. We find that the uptake of anthropogenic carbon dioxidereleased by human activitiesoccurred almost exclusively in the subtropical gyre. In contrast, natural carbon dioxide uptakewhich results from natural Earth system processesdominated in the subpolar gyre. We attribute the weakening of contemporary carbon dioxide uptake in the subpolar North Atlantic to a reduction in the natural component. We show that the slowdown of the meridional overturning circulation was largely responsible for the reduction in carbon uptake, through a reduction of oceanic heat loss to the atmosphere, and for the concomitant decline in anthropogenic CO 2 storage in subpolarwaters.