Earth and planetary system science, Comparative planetology
My research interest is to understand the stability, variability, and evolutionary trends of the Earth and other terrestrial planets,especially of their climates and surface environments (atmosphere,ocean, biosphere, crust, and upper mantle) from theoretical viewpoints, such as energy transport and geochemical cycles between the subsystems of the planets, on a variety of timescales. We have studied the evolution of the atmosphere coupled with the evolution of the ocean, crust and mantle as other components of the system. Mantle degassing is one of the fundamental processes for the evolution of the atmosphere and may depend both on the crustal production and the thermal evolution of the mantle. We have also studied correlations among the atmospheric, volcanic, and thermal evolution by using specific geochemical tracers, such as 40Ar, for the Earth, Mars, and Venus. Climatic change in the Earth's history may have been caused by variations in the atmospheric CO2 level. We have developed models of geochemical cycle of carbon on various time scales to reconstruct the paleoclimate changes and to understand the causes for the CO2 variations and climatic changes in the past. We have studied the climate evolution during the Earth's history and the climatic changes during some geological ages and within some geological boundary events (e.g., Permian/Triassic, Cenomanian/Turonian, Cretaceous/Tertiary, and Paleocene-Eocene thermal maximum). We also have developed an ocean biogeochemical general circulation model to study the carbon cycle at present. We are also interested in the snowball Earth events (global glaciations) during the Proterozoic. We have studied this issue from theoretical viewpoints (climate and carbon cycle modeling), and also, conducted geological field survey in Canada, US, and South Africa in order to reveal the relation among the climate change, evolution of the atmosphere, and evolution of life.
1. Ozaki, K., Tajika, E., Hong, P.K., Nakagawa, Y., and Reinhard, C.T. (2017) Primitive photosynthesis and Earth’s early climate system, Nature Geoscience, 11, 55–59, doi:10.1038/s41561-017-0031-2.