Response of deep-sea CaCO₃ sedimentation to Atlantic meridional overturning circulation shutdown

Changes in the distribution of the preservation and burial of calcium carbonate (CaCO₃) in deep ocean sediments and associated atmospheric pCO₂ response to the shutdown of the Atlantic meridional overturning circulation (MOC) are examined using an Earth system model. We find that shutdown of the Atlantic MOC forced by the freshwater inflow significantly decreases the CaCO₃ content in North Atlantic sediments. This is a consequence of a decrease in bottom-water carbonate ion concentrations and reduction in sea-surface CaCO₃ production. The main sedimentary impacts of these two effects are separated in time, however, with reduced CaCO₃ production dominating the decrease in CaCO₃ burial during the first 1000 years after the forcing is applied. In the absence of significant overturning circulation in the Atlantic, atmospheric pCO₂ increases by 11 ppm, largely due to a decrease in POC export and a weakening biological pump. The change in pCO₂ induced by reorganization of CaCO₃ burial in deep-sea sediments is small, only 1 ppm, because increased preservation of CaCO₃ in the Pacific largely efficiently buffers decreased preservation in the Atlantic, leaving the global burial and ocean alkalinity minimally changed at equilibrium.