The Northeast Atlantic is running out of excess carbonate in the horizon of cold-water corals communities.

The oceanic uptake of atmospheric carbon dioxide (CO₂) emitted by human activities alters the seawater carbonate system. Here, the chemical status of the Northeast Atlantic is examined by means of a high-quality database of carbon variables based on the GO-SHIP A25 section (1997–2018). The increase of atmospheric CO₂ leads to an increase in ocean anthropogenic carbon (C_ant) and a decrease in carbonate that is unequivocal in the upper and mid-layers (0–2,500 m depth). In the mid-layer, the carbonate content in the Northeast Atlantic is maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate and the arrival of subpolar-origin waters close to carbonate undersaturation. In this study we show a progression to undersaturation with respect to aragonite that could compromise the conservation of the habitats and ecosystem services developed by benthic marine calcifiers inhabiting that depth-range, such as the cold-water corals (CWC) communities. For each additional ppm in atmospheric pCO₂ the waters surrounding CWC communities lose carbonate at a rate of − 0.17 ± 0.02 μmol kg⁻¹ ppm⁻¹. The accomplishment of global climate policies to limit global warming below 1.5–2 ℃ will avoid the exhaustion of excess carbonate in the Northeast Atlantic. [ABSTRACT FROM AUTHOR]