The northeast atlantic is running out of excess carbonate: the fragile future of cold-water coral communities

XX Seminario Ibérico de Química Marina, SIQUIMAR 2020, Barcelona (Spain), 1st-3rd July 2020
Ocean acidification decreases the excess carbonate, that is, the amount of carbonate available for marine calcifiers. Here, the chemical status of the Northeast Atlantic and its cold-water corals (CWC) communities is examined by means of a high-quality database of carbon variables based on the GO-SHIP A25 section. The database covers a two-decade period (1997-2018), where the mean annual atmospheric carbon dioxide (CO2) increased from 364 to 409 parts per million of volume. The running out of excess carbonate, that is, the progression of undersaturation with respect to aragonite, could compromise the conservation of the habitats and ecosystem services developed by CWC communities. We find that the anthropogenic perturbation in the ocean carbon cycle is significantly decreasing the concentration of excess carbonate in the waters surrounding CWC communities at a rate of -0.17±0.02 μmol kg-1·ppm-1. The optimal chemical conditions for development of CWC communities in the Northeast Atlantic are maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate available and the arrival of subpolar-origin waters close to undersaturation. Given the current acidification rate, the living CWC communities would be exposed to undersaturated waters before the end of the century, if atmospheric CO2 concentration reached ~700 ppm. Therefore, the future of the CWC communities in the Northeast Atlantic is closely linked to the accomplishment of global climate policies to limit global warming below 1.5-2ºC, which would preserve chemically optimal conditions of CWC growth in this particular oceanic region
For this work M. Fontela was funded by the Spanish Ministry of Economy and Competitiveness (BES-2014-070449) supported by the Spanish Government and co-funded by the Fondo Europeo de Desarrollo Regional 2007–2012 (FEDER) and by Portuguese national funds from FCT - Foundation for Science and Technology through project UIDB/04326/2020 and CEECINST/00114/2018. F.F. Pérez were supported by the BOCATS Project (CTM2013-41048-P) and ARIOS project (CTM2016-76146-C3-1-R) both co-funded by the Spanish Government and the Fondo Europeo de Desarrollo Regional (FEDER). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989 (project COMFORT, Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points).”