著者

柏木 洋彦

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.126, no.4, pp.513-531, 2017-08-20 (Released:2017-09-27)

参考文献数

86

被引用文献数

2 2

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Weathering is deeply related to global climate change. In the carbon cycle, silicate weathering, especially volcanic rock weathering, transfers carbon in the atmosphere (as CO2) to the lithosphere, and oxidative weathering of organic matter releases carbon (as CO2) from the biosphere to the atmosphere. Moreover, as an indirect effect of weathering on climate change, negative feedback in the climate system, which results from the dependence of weathering rate on temperature and evolution of terrestrial plants, is crucial. It has stabilized the long-term global climate throughout the Phanerozoic. Weathering rate is controlled by several geochemical external factors: tectonic forces such as lithology, continental uplift, and continental drift (paleogeography); climate forces such as temperature, runoff, and glaciations; and, biological forces such as terrestrial plant evolution. Regarding biological forces, accelerated weathering assisted by ectomycorrhizal fungi (EM fungi) and arbuscular mycorrhizal fungi (AM fungi), as well as vascular plants of gymnosperms and angiosperm, are emphasized. Variations of global weathering in the geological past are estimated using experimental approaches, such as isotope analysis (e.g., 87Sr/86Sr, 187Os/186Os, δ7Li), and theoretical approaches, such as numerical simulations (e.g., carbon cycle model). Each is used differently according the purpose of a study. Based on these estimates, geological past climate changes in the Phanerozoic are found to be closely related to weathering. For example, on the order of magnitude of 107 years, changes in weathering patterns due to continental drift (paleogeography) have resulted in variations of atmospheric CO2, hence climate change. On the order of magnitude of 106 years, it is suggested that a decrease in atmospheric CO2 from the mid- to late Cretaceous was caused by enhanced weathering according to terrestrial plant evolution and that variations of atmospheric CO2 in the late Cenozoic were regulated by weathering directly or indirectly influenced by continental uplift. Additionally, contributions of weathering to global climate change involved in oceanic anoxic events in the Mesozoic have been investigated.

著者

鹿園 直建 原田 広康 池田 則生 柏木 洋彦

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.38, no.5, pp.149-160, 2009 (Released:2009-11-26)

参考文献数

20

被引用文献数

3 3

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Dissolution kinetics model calculations were performed for the interaction between three types of basaltic rocks in Japan (Fuji and Hachijyojima fresh basalts and Kitamatsuura altered basalt) and groundwater injected CO2. Dissolution rates of the basalts experimentally determined by the authors (Shikazono et al., 2008) and database of dissolution rate constants of silicate minerals in the basaltic rocks in PATHARC (Talman et al., 2000) were used for the calculations. The results of calculations indicate that most of dissolved carbon in groundwater injected CO2 can be fixed as carbonates in long-term period. The efficiency of carbon fixation is in an order, Hachijyojima>Fuji>Kitamatsuura. But the efficiency is not so different for three basaltic rocks in the fixation of carbon in underground sequestration of CO2. It is inferred that mineral trapping of CO2 by carbonates in basalt aquifer is useful for the long-term fixation of carbon in underground sequestration of CO2.

著者

柏木 洋彦 鹿園 直建

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.112, no.4, pp.473-488, 2003-08-25 (Released:2009-11-12)

参考文献数

85

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Climate change and variations of atmospheric CO2 during Cenozoic have been discussed by many studies. The model results for global carbon cycle and climate change are generally consistent with those of many analytical studies concerning climate events in early Cenozoic, e.g., early Eocene warming events. However, the climate events proposed by analytical studies in late Cenozoic are not wholly inconsistent with the results of the model studies, e.g., Miocene climatic optimum (warming), cooling events in Eocene/Oligocene boundary and middle Miocene (15 Ma). Many problems remain in relation to evaluating CO2 flux by hydrothermal solutions at mid-ocean ridges, island-arc, and back-arc basins in the models. Also, the discrepancy may be derived from errors in estimating weathering flux, organic carbon burial, and change in vegetation. Moreover, another greenhouse effect gas such as methane, land-sea distribution, albedo variations due to the formation of ice-sheets, and temperature distribution attributed to changes in the ocean circulation system should be considered. Recent analytical studies reveal that the CO2 level since Miocene has remained relatively low in spite of the suggested climate events in this period. The mechanism of oceanic environmental change, as well as atmospheric CO2, is especially important to elucidate climate change during Cenozoic.