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

Abstract

[1] Changes in the distribution of the preservation and burial of calcium carbonate (CaCO 3 ) in deep ocean sediments and associated atmospheric pCO 2 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 CaCO 3 content in North Atlantic sediments. This is a consequence of a decrease in bottom-water carbonate ion concentrations and reduction in sea-surface CaCO 3 production. The main sedimentary impacts of these two effects are separated in time, however, with reduced CaCO 3 production dominating the decrease in CaCO 3 burial during the first 1000 years after the forcing is applied. In the absence of significant overturning circulation in the Atlantic, atmospheric pCO 2 increases by 11 ppm, largely due to a decrease in POC export and a weakening biological pump. The change in pCO 2 induced by reorganization of CaCO 3 burial in deep-sea sediments is small, only 1 ppm, because increased preservation of CaCO 3 in the Pacific largely efficiently buffers decreased preservation in the Atlantic, leaving the global burial and ocean alkalinity minimally changed at equilibrium.

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“…The results confirm that the nutrient-burial feedback identified by Tschumi et al (2011) should not be neglected (e.g. Sigman et al, 1998;Matsumoto et al, 2007;Chikamoto et al, 2008) when discussing long-term carbon cycle changes. This nutrient-burial feedback arising as marine biological productivity in the long run is limited by the riverine or aeolian input of nutrients into the ocean.…”

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