Meridional overturning circulation conveys fast acidification to the deep Atlantic Ocean
Published 13 February 2018
Since the Industrial Revolution, the North Atlantic Ocean has been accumulating anthropogenic carbon dioxide (CO2) and experiencing ocean acidification1, that is, an increase in the concentration of hydrogen ions (a reduction in pH) and a reduction in the concentration of carbonate ions. The latter causes the ‘aragonite saturation horizon’—below which waters are undersaturated with respect to a particular calcium carbonate, aragonite—to move to shallower depths (to shoal), exposing corals to corrosive waters2,3. Here we use a database analysis to show that the present rate of supply of acidified waters to the deep Atlantic could cause the aragonite saturation horizon to shoal by 1,000–1,700 metres in the subpolar North Atlantic within the next three decades. We find that, during 1991–2016, a decrease in the concentration of carbonate ions in the Irminger Sea caused the aragonite saturation horizon to shoal by about 10–15 metres per year, and the volume of aragonite-saturated waters to reduce concomitantly. Our determination of the transport of the excess of carbonate over aragonite saturation (xc[CO32−])—an indicator of the availability of aragonite to organisms—by the Atlantic meridional overturning circulation shows that the present-day transport of carbonate ions towards the deep ocean is about 44 per cent lower than it was in preindustrial times. We infer that a doubling of atmospheric anthropogenic CO2 levels—which could occur within three decades according to a ‘business-as-usual scenario’ for climate change4—could reduce the transport of xc[CO32−] by 64–79 per cent of that in preindustrial times, which could severely endanger cold-water coral habitats. The Atlantic meridional overturning circulation would also export this acidified deep water southwards, spreading corrosive waters to the world ocean.
Perez F. F., Fontela M., García-Ibáñez M. I., Mercier H., Velo A., Lherminier P., Zunino P., de la Paz M., Alonso-Pérez F., Guallart E. F. & Padin X. A., in press. Meridional overturning circulation conveys fast acidification to the deep Atlantic Ocean. Nature.
As the saturation horizon rises so too the long term sink for carbonates is reduced in size. For the short time spans we humans tend to worry about this may not seem catastrophic but it is a a problem that earth will have to deal with for ~ 100,000 years after we finally quit emitting CO2. The calcium carbonate that would otherwise settle onto the shelves will instead desolve and reenter the oceans as DIC . The DIC will circulate and eventually upwell where it can again enter the atmospheric carbon pool. Our legacy is a very long term truncation of the ability of the oceans to sink carbon. Sad that, a legacy of death.
Bruce