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The Paleocene-Eocene Thermal Maximum was a transient, carbon-induced global warming event, considered the closest analog to ongoing climate change. Impacts of a decrease in deepwater formation during the onset of the Paleocene-Eocene Thermal Maximum suggested by proxy data on the carbon cycle are not yet fully understood. Using an Earth System Model, we find that changes in overturning circulation are key to reproduce the deoxygenation and carbonate dissolution record. Weakening of the Southern Ocean deepwater formation and enhancement of ocean stratification driven by warming cause an asymmetry in carbonate dissolution between the Atlantic and Pacific basins suggested by proxy data. Reduced ventilation results in accumulation of remineralization products (CO2 and nutrients) in intermediate waters, thereby lowering O-2 and increasing CO2. As a result, carbonate dissolution is triggered throughout the water column, while the ocean surface remains supersaturated. Our findings contribute to understanding of the long-term response of the carbon cycle to climate change.

Plan Language Summary The Paleocene-Eocene Thermal Maximum, characterized by a relatively rapid carbon release to the atmosphere and global warming, has received ample scientific attention owing to its analogy to ongoing climate change. We perform Earth system model projections of concomitant changes in climate, ocean circulation, and marine biogeochemical cycles during the onset of the Paleocene-Eocene Thermal Maximum. In our simulations global warming (induced by atmospheric emissions of CO2) leads to a weakening of the meridional overturning circulation and reduced ventilation of the ocean interior which is more pronounced in the Atlantic than in the Pacific Ocean. As a result of this ocean stagnation, respiratory CO2 released via bacterial remineralization of organic matter (oxygen is thereby consumed) builds up in intermediate waters. This triggers carbonate dissolution and deoxygenation. This mechanism alone is sufficient to explain the asymmetry in the carbonate dissolution proxy record between the Pacific and Atlantic Oceans.