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Atlantic Ocean CO₂ uptake reduced by weakening of the AMOC

Between 1990 and 2006 there was a rapid decline in the amount of carbon dioxide taken up by the subpolar Atlantic Ocean from the atmosphere, related to warming at the surface of the ocean. The results from model simulations indicated there was a reduced meridional overturning circulation of the Atlantic Ocean (AMOC) at the same time as the reduced CO₂ levels. It has been uncertain to what extent the slowing of the circulation system, that is responsible for transporting warm surface waters to the northern high latitudes, and deep waters that are cool to the south, contributed to the uptake of carbon. The authors¹ tracked the uptake of CO₂ in the subtropical and subpolar regions of the North Atlantic Ocean for the last 2 decades by using data on the oceanic transport of volume, heat and CO₂. They assumed that the natural part of the carbon involved related to the atmospheric levels in the preindustrial atmosphere, the remainder being the proportion that is anthropogenic carbon, thereby separating the natural carbon from the anthropogenic carbon. Their results showed that the CO₂ released by human activity occurred almost exclusively in the in the subtropical gyre.

They also found that the uptake of natural CO₂, that is the result of processes that are part of the Earth system, was the dominant CO₂ component in the subpolar gyre. According to the authors¹ they attributed the reduced uptake of contemporary CO₂ in the subpolar region of the of the North Atlantic to the reduction of the natural component. They suggest their results show that the CO₂ uptake reduction was largely the result of the slowing of the meridional overturning circulation, by a reduction of heat loss from the ocean to the atmosphere, and a concomitant decline of the storage in subpolar waters of the anthropogenic CO₂,

It has been estimated that the global ocean takes up contemporary CO₂ 1.6 ± 0.9 PgCyr^-1 from observation-based CO₂ flux climatology referenced to the year 2000.

Sources & Further reading

1. Perez, Fiz F., Herle Mercier, Marcos Vazquez-Rodriguez, Pascale Lherminier, Anton Velo, Paula C. Pardo, Gabriel Roson, and Aida F. Rios. "Atlantic Ocean Co2 Uptake Reduced by Weakening of the Meridional Overturning Circulation." Nature Geosci 6, no. 2 (02//print 2013): 146-52.