Multicentury climate warming slows meridional overturning circulation, sequestering nutrients in the deep ocean and reducing uptake of anthropogenic CO2

Under a high-end emission scenario to the year 2300, climate warming drives a drastic slowdown in the ocean’s meridional overturning circulation, with a cessation of Antarctic Bottom Water (AABW) production and North Atlantic Deep Water (NADW) formation reduced to 5 Sv.  In conjunction with regionally enhanced biological production and upper-ocean nutrient trapping in the Southern Ocean, this deep circulation slowdown drives long-term sequestration of nutrients and dissolved inorganic carbon in the deep ocean, but also greatly reduces the ocean’s capacity to take up heat and anthropogenic CO₂ from the atmosphere, prolonging peak warmth climate conditions. Surface nutrients (N, P, and Si) are steadily depleted driving down biological productivity and weakening the biological pump, which transfers carbon to the ocean interior.  Ocean dissolved oxygen concentrations steadily decline, with the potential for anoxia eventually developing in some regions.  This Community Earth System Model (CESM) simulation did not include active ice sheet dynamics, but the strong climate warming simulated would lead to large freshwater discharge from the Antarctic and Greenland ice sheets.  This would further stratify the polar regions, potentially leading to complete shutdown of the meridional overturning circulation.  The impacts of this would be catastrophic as the hothouse Earth climate conditions could be extended for thousands of years, with widespread ocean anoxia developing, driving a mass extinction event.