5:15 PM - 6:45 PM
[MIS12-P13] Ocean carbon pump response during the glacial period and its effect on atmospheric carbon dioxide concentration
Keywords:Oecan carbon cycle, glacial-interglacial cycle, Ocean tracer model, Ocean general circulation model
The ocean is a huge carbon reservoir and has a major impact on the climate system. Paleo reconstructions show that glacial atmospheric carbon dioxide concentrations were about 90ppm lower than that in the preindustrial. (e,g. Lüthi et al., 2008). This is thought to be caused by increasing carbon storage during glacial periods. Many modeling studies have been conducted to explain the reduction in glacial atmospheric carbon dioxide concentrations, but the quantitative contributions of individual processes are controversial, and the glacial simulations using GCMs show only about the half pCO2 reduction of the data presented by the paleo reconstructions. It has been pointed out that the model-data agreement of Southern Ocean properties is crucial for simulating glacial changes in the ocean carbon cycle. Against this background, Kobayashi et al.(2021) show a 77-ppm reduction of the atmospheric pCO2 by considering carbonate compensation, and salinity stratification., which closely matches the paleo record.
This study aims to determine the processes for the reduction of the glacial atmospheric pCO2 through ocean carbon pump decomposition by Oka(2020) using the results of Kobayashi et al.(2021), and its predecessor Kobayashi et al.(2015). They performed four experiments: control, restoring(the ERW), and stratification(the ERWs and the ERWa). Restoring and stratification experiments were performed to examine the response of the high salinity in the deep Southern Ocean and stratification. In the ERW experiment, salinity in the deepest layer was restored toward high salinity in the Weddell Sea and Ross Sea. They chose 37.0 and 38.0 psu as the restoring values of salinity. In the ERWs experiment, the vertical diffusion coefficient in the Southern Ocean(30-90S) was forced to be a constant value of 0.10, and in the ERWa experiments the one was forced to be a constant value of 0.10. In this study, these ERW, ERWs, ERWa, and control LGM and PI experiments were analyzed by ocean carbon pump decomposition.
Compared to PI, the atmospheric pCO2 was reduced by 44.1 ppmv in the control LGM experiment and by 39 ppmv, 50.5 ppmv, and 57.2 ppmv in ERW, ERWs, and ERWa respectively. The reduction in atmospheric pCO2 is caused by changes in temperature, salinity, and the ocean carbon pump. The ocean carbon pump has four processes: organic matter pump, carbonate pump, gas exchange pump, and freshwater flux pump, which can be quantitatively analyzed by ocean carbon pump decomposition. In the control LGM experiment, the organic matter pump, carbonate pump, and gas exchange pump contributed to the reductions in pCO2 of 11.6 ppmv, -1.4 ppmv, and 6.2 ppmv compared to PI. Note that the negative sign indicates an increase in the atmospheric pCO2 Also, pump contribution is 4.1ppmv, -2.4ppmv, and 4.0ppmv in the ERW experiment, and 11.4ppmv, -6.8ppmv and 4.2ppmv in the ERWs experiment and 11.5ppmv, -6.9ppmv and 4.2ppmv in the ERWa experiment in order of the organic pump, carbonate pump and gas exchange pump The freshflux water pumps did not significantly change the atmospheric pCO2. These results indicated that the organic matter pump is the most important factor in reducing atmospheric carbon dioxide concentrations. Comparing the strength among the organic pumps, the control LGM experiments, the ERWa experiment, the ERWs experiment, and the ERW experiment were stronger in that order. In the carbonate pumps, the more stratified the experiment, the stronger the pump. Gas exchange pumps weakened compared to PI, contributing to increased atmospheric pCO2. Comparisons among gas exchange pumps showed that the control LGM, ERW, ERWs, and ERWa experiments were weaker, in that order. Freshwater flux pumps contributed little to the reduction in carbon dioxide concentrations.The presentation will discuss these results to determine under what conditions pump strengthening or weakening occurs and its geographic distribution.
This study aims to determine the processes for the reduction of the glacial atmospheric pCO2 through ocean carbon pump decomposition by Oka(2020) using the results of Kobayashi et al.(2021), and its predecessor Kobayashi et al.(2015). They performed four experiments: control, restoring(the ERW), and stratification(the ERWs and the ERWa). Restoring and stratification experiments were performed to examine the response of the high salinity in the deep Southern Ocean and stratification. In the ERW experiment, salinity in the deepest layer was restored toward high salinity in the Weddell Sea and Ross Sea. They chose 37.0 and 38.0 psu as the restoring values of salinity. In the ERWs experiment, the vertical diffusion coefficient in the Southern Ocean(30-90S) was forced to be a constant value of 0.10, and in the ERWa experiments the one was forced to be a constant value of 0.10. In this study, these ERW, ERWs, ERWa, and control LGM and PI experiments were analyzed by ocean carbon pump decomposition.
Compared to PI, the atmospheric pCO2 was reduced by 44.1 ppmv in the control LGM experiment and by 39 ppmv, 50.5 ppmv, and 57.2 ppmv in ERW, ERWs, and ERWa respectively. The reduction in atmospheric pCO2 is caused by changes in temperature, salinity, and the ocean carbon pump. The ocean carbon pump has four processes: organic matter pump, carbonate pump, gas exchange pump, and freshwater flux pump, which can be quantitatively analyzed by ocean carbon pump decomposition. In the control LGM experiment, the organic matter pump, carbonate pump, and gas exchange pump contributed to the reductions in pCO2 of 11.6 ppmv, -1.4 ppmv, and 6.2 ppmv compared to PI. Note that the negative sign indicates an increase in the atmospheric pCO2 Also, pump contribution is 4.1ppmv, -2.4ppmv, and 4.0ppmv in the ERW experiment, and 11.4ppmv, -6.8ppmv and 4.2ppmv in the ERWs experiment and 11.5ppmv, -6.9ppmv and 4.2ppmv in the ERWa experiment in order of the organic pump, carbonate pump and gas exchange pump The freshflux water pumps did not significantly change the atmospheric pCO2. These results indicated that the organic matter pump is the most important factor in reducing atmospheric carbon dioxide concentrations. Comparing the strength among the organic pumps, the control LGM experiments, the ERWa experiment, the ERWs experiment, and the ERW experiment were stronger in that order. In the carbonate pumps, the more stratified the experiment, the stronger the pump. Gas exchange pumps weakened compared to PI, contributing to increased atmospheric pCO2. Comparisons among gas exchange pumps showed that the control LGM, ERW, ERWs, and ERWa experiments were weaker, in that order. Freshwater flux pumps contributed little to the reduction in carbon dioxide concentrations.The presentation will discuss these results to determine under what conditions pump strengthening or weakening occurs and its geographic distribution.