11:30 AM - 11:45 AM
[MIS14-18] Impact of Ocean Physical Conditions on Ocean Carbon Pumps and Atmospheric CO2 Concentration at the Last Glacial Maximum
Keywords:carbon , Last glacial maximum, Ocean general circulation model
Ice core records reveal that atmospheric CO2 partial pressure(pCO2) have fluctuated with temperature and ice sheet volume during glacial-interglacial cycles over the past 800,000 years. Glacial CO2 levels are approximately 100 ppmv lower than those of interglacial periods. Due to colder and drier climates, terrestrial vegetation likely decreased and was stored in the ocean interior rather than in terrestrial reservoirs or the atmosphere, driven by deviations from modern ocean circulation patterns(Schmitter and Galbraith, 2008; Gottshalk et al., 2019; Kobayashi et al., 2015)
Due to colder and drier climates, terrestrial vegetation likely decreased during galcial periods compared to the present(e.g. Peterson et al., 2014). As a result CO2 was absorbed and stored in the ocean interior rather than in terrestrial reservoirs or the atmosphere driven by deviations from modern ocean circulation patterns Schmitter and
Galbraith 2008 Gottschalk et al., 2019, Kobayashi et al., 2015)
To clarify the mechanisms behind atmosphere CO2 changes in response to ocean circulation variations three-dimensional climate models are necessary to reconstruct glacial ocean physical conditions and analyze their relationships with atmospheric CO2 levels. However previous studies using such models have struggled to reproduce ocean physical states consistent with paleoclimate proxies such as stratification structures and weakened AMOC. Additionally, the simulated rediction in atmospheric CO2 from the preindustrial(PI) period to the Last Glacial Maximum(LGM) tends to be underestimated compared to ice core data indicating a potential link to the
reprodicibility of ocean physical conditions.
This study investigates how uncertainties in ocean physical conditions affect the simulation of pCO2(atm) by concluding numerical experiments using a three-dimensional ocean carbon cycle model. The response of pCO2(atm) to different ocean physical fields derived from 11 PMIP model outputs was analyzed. Using carbon pump decomposition methods(Sarmiento and Gruber 2006, Oka 2020), We quantitavely evaluated the contributions of various carbon pumps, including the biological pump, carbonate pump, gas exchange pum and fresh water pump to the reduction of pCO2(atm). These experiments identified key circulation changes necessary to reproduce low pCO2(atm) during glacial periods. Furthermore model results were compared with paleoclimate proxies to assess the validity of simulated pCO2(atm) impacts.
Our results indicate that reduction in pCO2(atm) from PI to the LGM was limited to a maximum of 50ppmv with variations of approximately 20ppmv depending on physical states among models. We further analysed the factors behind this variation focusing on changes in CO2 solubility and ocean carbon pumps.
First changes in CO2 solubility were primarily influenced by the reproducibility of sea surface temperature SST. The SST reduction from PI to LGM ranged from 1.5K to 2.7K with variations of about 1.2K among models resulting in differences of up to 20ppmv in pCO2(atm) reduction. Comparisons with SST reconstructions from proxies indicated that PMIP models tended to underestimate SST.
Second differences in ocean carbon pumps were influenced by AMOC and SST reproducibility in the North Atlantic. The biological pump reduced pCO2 atm by 10 to 30 ppmv with a 20 ppmv difference depending on AMOC reproducibility. Furthermore reductions in pCO2 atm due to ocean carbon pumps correlated with deep water massage older water masses tended to be associated with greater pCO2 atm reductions. However model-derived water massages were significantly younger compared to radiocarbon 14C proxy records.
These findings highlight the underestimations of sst and the failure to reproduce older water messages in the LGM, contributing to underestimations of pCO2(atm) reductions. This underscores the importance of accurately reproducing ocean physical states, which may require enhancements in atmospheric model parametrizations and better modeling of processes like deep-water formation near Antarctica. Additionally, beyond physical state reproducibility, pCO2(atm) may have been influenced by changes in the marine ecosystem. Further research should address these issues by improving representations of physical and biogeochemical processes in models.
Due to colder and drier climates, terrestrial vegetation likely decreased during galcial periods compared to the present(e.g. Peterson et al., 2014). As a result CO2 was absorbed and stored in the ocean interior rather than in terrestrial reservoirs or the atmosphere driven by deviations from modern ocean circulation patterns Schmitter and
Galbraith 2008 Gottschalk et al., 2019, Kobayashi et al., 2015)
To clarify the mechanisms behind atmosphere CO2 changes in response to ocean circulation variations three-dimensional climate models are necessary to reconstruct glacial ocean physical conditions and analyze their relationships with atmospheric CO2 levels. However previous studies using such models have struggled to reproduce ocean physical states consistent with paleoclimate proxies such as stratification structures and weakened AMOC. Additionally, the simulated rediction in atmospheric CO2 from the preindustrial(PI) period to the Last Glacial Maximum(LGM) tends to be underestimated compared to ice core data indicating a potential link to the
reprodicibility of ocean physical conditions.
This study investigates how uncertainties in ocean physical conditions affect the simulation of pCO2(atm) by concluding numerical experiments using a three-dimensional ocean carbon cycle model. The response of pCO2(atm) to different ocean physical fields derived from 11 PMIP model outputs was analyzed. Using carbon pump decomposition methods(Sarmiento and Gruber 2006, Oka 2020), We quantitavely evaluated the contributions of various carbon pumps, including the biological pump, carbonate pump, gas exchange pum and fresh water pump to the reduction of pCO2(atm). These experiments identified key circulation changes necessary to reproduce low pCO2(atm) during glacial periods. Furthermore model results were compared with paleoclimate proxies to assess the validity of simulated pCO2(atm) impacts.
Our results indicate that reduction in pCO2(atm) from PI to the LGM was limited to a maximum of 50ppmv with variations of approximately 20ppmv depending on physical states among models. We further analysed the factors behind this variation focusing on changes in CO2 solubility and ocean carbon pumps.
First changes in CO2 solubility were primarily influenced by the reproducibility of sea surface temperature SST. The SST reduction from PI to LGM ranged from 1.5K to 2.7K with variations of about 1.2K among models resulting in differences of up to 20ppmv in pCO2(atm) reduction. Comparisons with SST reconstructions from proxies indicated that PMIP models tended to underestimate SST.
Second differences in ocean carbon pumps were influenced by AMOC and SST reproducibility in the North Atlantic. The biological pump reduced pCO2 atm by 10 to 30 ppmv with a 20 ppmv difference depending on AMOC reproducibility. Furthermore reductions in pCO2 atm due to ocean carbon pumps correlated with deep water massage older water masses tended to be associated with greater pCO2 atm reductions. However model-derived water massages were significantly younger compared to radiocarbon 14C proxy records.
These findings highlight the underestimations of sst and the failure to reproduce older water messages in the LGM, contributing to underestimations of pCO2(atm) reductions. This underscores the importance of accurately reproducing ocean physical states, which may require enhancements in atmospheric model parametrizations and better modeling of processes like deep-water formation near Antarctica. Additionally, beyond physical state reproducibility, pCO2(atm) may have been influenced by changes in the marine ecosystem. Further research should address these issues by improving representations of physical and biogeochemical processes in models.