3:00 PM - 3:15 PM
[AOS19-06] Modeling of the glacial ocean carbon cycle with an ocean general circulation model
Keywords:ocean carbon cycle, glacial-interglacial cycle, global ocean meridional overturning circulation, carbonate compensation process
The difference in pCO2atm between the preindustrial control simulation and the LGM control simulation was 44.1 ppm. Changes in solubility depending on sea surface temperature and salinity, ocean circulation, and biological production in the ocean surface layers due to iron fertilization resulted in the reduction of pCO2atm , but all of the variation of glacial pCO2atm could not be explained in our control experiment as in previous studies. LGM control simulation underestimated the salinity and water mass age suggested by proxy data in the Southern Ocean. We thus curried out a sensitivity experiment (LGM stratification experiment) to reproduce the salinity and water mass age in the glacial deep Southern Ocean suggested by LGM proxy data. In the LGM stratification experiment, sea bottom salinity around the Antarctica was restored to the high salinity to mimic the deep water formation process. In addition, we decreased vertical diffusivity considering the enhanced salinity stratification in the glacial Southern Ocean.
High salinity in the deep Southern Ocean resulted in increased pCO2atm because Antarctic Bottom Water flow increased and residence time of carbon decreased in the deep Pacific. On the other hand, weakening of vertical mixing contributed to the increase of the vertical gradient of dissolved inorganic carbon and decrease of pCO2atm. However, it is unable to explain the full magnitude of recorded reduction of glacial pCO2atm in our simulations which include the above-mentioned contribution of the Southern Ocean process in addition to gas-exchange, ocean circulation, and iron fertilization changes [Kobayashi et al., 2015].
Carbonate compensation process has been reported to amplify the variation of glacial–interglacial ocean carbon cycle but it is not explicitly included in our above-mentioned simulations. We now try to evaluate the role of carbonate compensation process by coupling a newly developed simple sediment model with our OGCM.