4:45 PM - 5:00 PM
[MIS10-34] Role of ocean carbon cycle in glacial reduction of atmospheric carbon dioxide concentration
Keywords:ocean carbon cycle, glacial-interglacial cycle, global ocean meridional overturning circulation, carbonate compensation process
I first try to improve the insufficient reproducibility of the high salinity and old water mass in the glacial deep Southern Ocean, and then investigate its influence on the ocean carbon cycle and atmospheric pCO2. For this purpose, a LGM simulation is conducted, in which salinity in the ocean deepest layer in the Southern Ocean is restored toward high salinity reported from paleo-ocean proxy data and small vertical diffusion coefficient is prescribed to reproduce the enhanced stratification in the Southern Ocean. In the simulated glacial Southern Ocean, salinity stratification is strengthened, and the residence time of deep water gets longer. As a consequence, the concentration of dissolved inorganic carbon (DIC) increases in the Southern Ocean and decreases in the surface ocean glacial decline in atmospheric pCO2 is only about 47 ppm.
Next, the role of carbonate compensation process in the glacial reduction of atmospheric pCO2 is investigated with a newly created ocean sediment model. As a result of carbonate compensation, atmospheric pCO2 decreases due to an increase in whole ocean alkalinity as previous studies suggested. It is newly found that this carbonate compensation process works more effectively by the enhanced stratification in the Southern Ocean. Owing to this contribution, the glacial reduction of atmospheric pCO2 reaches about 73 ppm, which is much larger response than that obtained in previous OGCM studies.