Current CaCO₃ dissolution at the seafloor caused by anthropogenic CO₂

Oceanic uptake of anthropogenic CO₂ leads to decreased pH, carbonate ion concentration, and saturation state with respect to CaCO₃ minerals, causing increased dissolution of these minerals at the deep seafloor. This additional dissolution will figure prominently in the neutralization of man-made CO₂ However, there has been no concerted assessment of the current extent of anthropogenic CaCO₃ dissolution at the deep seafloor. Here, recent databases of bottom-water chemistry, benthic currents, and CaCO₃ content of deep-sea sediments are combined with a rate model to derive the global distribution of benthic calcite dissolution rates and obtain primary confirmation of an anthropogenic component. By comparing preindustrial with present-day rates, we determine that significant anthropogenic dissolution now occurs in the western North Atlantic, amounting to 40-100% of the total seafloor dissolution at its most intense locations. At these locations, the calcite compensation depth has risen ∼300 m. Increased benthic dissolution was also revealed at various hot spots in the southern extent of the Atlantic, Indian, and Pacific Oceans. Our findings place constraints on future predictions of ocean acidification, are consequential to the fate of benthic calcifiers, and indicate that a by-product of human activities is currently altering the geological record of the deep sea.