Impact of the Ocean’s Overturning Circulation on Atmospheric CO2

• Main Authors: Schmittner, Andreas, Brook, Edward J., Ahn, Jinho
• Format: Book Part
• Language: English; unknown
• Published: American Geophysical Union
• Subjects: Antarc*; Antarctic; ice core; North Atlantic; Southern Ocean
• Online Access: https://ir.library.oregonstate.edu/concern/defaults/z603qz979

A coupled climate-carbon cycle model and ice core CO2 data from the last glacial period are used to explore the impact of changes in ocean circulation on atmospheric CO2 concentrations on millennial time scales. In the model, stronger wind driven circulation increases atmospheric CO2. Changes in the buoyancy driven deep overturning in the Atlantic affect atmospheric CO2 only indirectly through their effect on Southern Ocean stratification. In simulations with an abrupt and complete shutdown of the Atlantic overturning, stratification in the Southern Ocean decreases due to salinification of surface waters and freshening of the deep sea. Deeper mixed layers and steeper isopycnals lead to outgassing of CO2 in the Southern Ocean and hence gradually increasing atmospheric CO2 concentrations on a multi-millennial time scale. The rise in CO2 terminates at the time of rapid resumption of deep water formation and warming in the North Atlantic, and CO2 levels subsequently gradually decrease. These model responses and a strong correlation between simulated atmospheric CO2 and Antarctic surface air temperatures with little or no time lag are consistent with newly synchronized ice core data from the last ice age. Sensitivity experiments reveal that the amplitude of the response of atmospheric CO2 is sensitive to the model background climatic state and decreases in a colder climate owing to smaller changes in the overturning. Keywords: modeling, atmospheric CO2, Southern Ocean, climate dynamics, ocean circulation