第三紀気候変動に対するグローバル二酸化炭素循環の影響 Influence of Global Carbon Dioxide Cycle on Tertiary Climate Change
The geochemical and geological studies of climate change in the Tertiary age indicate that temperature is controlled by the combined processes of global CO<SUB>2</SUB> cycle (weathering, hydrothermal-igneous activities, metamorphism), ocean circulation, albedo, and development of continental ice-sheet.<BR>The temperature change during the Tertiary age has been estimated from analytical data (paleontological data and oxygen isotope data on foraminifera), and computer simulations of the global CO<SUB>2</SUB> cycle. The analytical studies indicate that the middle Miocene age (15-16 Ma) had the climatic optimum. This could be related to the increased rate of CO<SUB>2</SUB> degassing, which was caused by intense hydrothermal-igneous activities at back arc basins, change of mode of plate subduction, and change of ocean circulation pattern. High temperatures in the early Tertiary age (Eocene) are considered to have been also related to CO<SUB>2</SUB> degassing by intense hydrothermal, igneous, and metamorphic activities. The decrease of temperature since the middle Miocene age could have been caused by the combined processes of development of ice sheet, changes in ocean circulation patterns, and intense weathering rate related to the uplifting of the Himalayas.