Geochemistry, Palaeoclimatology, Palaeoceanography
The global environment is a gigantic and complex system composed from a large number of sub-systems connected each other. Both long- and short-term geological processes affected to the surface phenomena. The studies that I am currently involved are to understand their mechanisms using combined Geochemical and Geophysical approaches.
The research topics that I am currently interesting are as follows:1. Study on Palaeoclimatology2. Sea-level changes3. Geomagnetic intensity variations and cosmogenic nuclides production rates4. Sea-water Uranium series nuclides chemistry(Uranium in corals, sediments and sea-water)5. Geo-archaeology(People’s migration from Africa, Landbridge problem, Dating of human artifacts)6. Tectonics and climate change(Active tectonics research using cosmogenic nuclides and/or GPS)
Understanding the past climate change is the important approach to predict future changes. In particular, since the industrial revolution, people’s induced greenhouse gases have largely perturbed earth’s climate system. To predict future climate changes, the precise reconstruction of the past changes free from people’s activity effects using geological archives are particularly important which can be used as boundary conditions for the General Circulation Models. Therefore, one of the goal of my study is to provide accurate records of past climate changes using geochemical and geophysical methods. Cores taken from deep seas contained details of environmental changes in the past and hence they are widely used for my research. Coral reefs are also important to study climate change that can be used to detect surface ocean environmental changes with using various chemical tracers. Studies regarding the global chemical cycles are included in this category.
My interests are extended to those included understanding the physical properties of the earth’s mantle and crust. Surface environmental processes are key to understand the internal structure of the earth. Searching for the paleo-geoidal information such as ups and downs of the past shoreline structures, for examples, is an approach to attack this type of problem. Systematic study to monitor rebounding the earth’s surface due to ice- and meltwater- loads caused by glacial and interglacial climate changes could tell us the rheological structure of its interior. Crustal uplift due to tectonic process can be studied using cosmogenic nuclides to monitor long-term history, whereas GPS systems are now widely used to study annual movements of the crusts. Integration of these two approaches is the crucial issue and the best outcomes would be the perfect reconciliations of both results. Yet it is not the case in many cases so gathering the higher-resolution datasets are still important topic.
So my research interests are to study the recent history of earth. The tools to undertake researches are various and I am eager to expand them as analytical methods being advanced. The bottom line when I conduct my research topics is as recognizing the geological phenomena using macro- as well as micro-views.
I am a member of the International Liaison Office of the School of Science and try to promote international exchange programs including collaborative projects.
1. Yokoyama, Y. et al.(2018) Rapid glaciation and a two-step sea level plunge into the Last Glacial Maximum. Nature, 559, 603-607
2. Lee, C., Yokoyama, Y. et al.(2016) Two-step rise of atmospheric oxygen linked to the growth of continents. Nature Geoscience, 9, 417-424
3. Yokoyama, Y. et al.(2016) Widespread collapse of the Ross Ice Shelf during the late Holocene. PNAS (Proceedings of National Academy of Science USA), 113 (9), 2354-2359