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Tatsuya Hayashi Last modified date:2019.09.05

Assistant Professor / Department of Environmental Changes
Department of Environmental Changes
Faculty of Social and Cultural Studies


Graduate School


E-Mail
Phone
092-802-5655
Academic Degree
Ph.D
Country of degree conferring institution (Overseas)
No
Field of Specialization
Micropaleontology, Paleoclimatology
Outline Activities
My interests are taxonomy, evolution and ecology of marine and non-marine diatoms and their relationship with Cenozoic climatic and environmental changes.
I am also interested in the reconstruction of Cenozoic paleoclimatic and environmental records based on multi-proxy studies on marine and lake sediments.
Research
Research Interests
  • Late Cenozoic evolutionary history of planktonic diatoms
    keyword : nonmarine diatoms, late Cenozoic, evolution
    2012.04.
  • Intensification of Northern hemisphere glaciation and glacial-interglacial cycles over the past 3 Myr
    keyword : Northern hemisphere glaciation, glacial-interglaical cycles, North Atlantic, AMOC
    2007.04.
  • Middle to Late Pleistocene Indian monsoon changes and environmental changes in the Kathmandu Basin, Nepal
    keyword : Indian monsoon, fossil diatoms, Paleo-Kathmandu Lake, Middle to Late Pleistocene, Nepal
    2000.04.
Academic Activities
Papers
1. Tatsuya Hayashi, William N. Krebs, Megumi Saito-Kato, Yoshihiro Tanimura, The turnover of continental planktonic diatoms near the middle/late Miocene boundary and their Cenozoic evolution, PLoS ONE, doi.org/10.1371/journal.pone.0198003, 13, 6, e0198003, 2018.06, [URL], Fossil evidence indicates that modern assemblages of temperate nonmarine planktonic diatoms began near the middle/late Miocene boundary when the genus Actinocyclus, an important constituent of lacustrine planktonic diatom assemblages during the early to middle Miocene, was replaced by genera of the family Stephanodiscaceae. This floral turnover has been confirmed in many regions of the world, except eastern Asia where taxonomic data about early and middle Miocene planktonic diatom assemblages have until recently been scarce. Our analysis of Lower and Middle Miocene lacustrine diatomaceous rocks in Japan confirms that species of nonmarine Actinocyclus were important constituents of lake phytoplankton there as well. The appearance of nonmarine Actinocyclus species near the beginning of the Miocene may have resulted from the introduction of euryhaline species into lacustrine environments during a highstand of sea level at that time. Similarly, it is possible that species of Stephanodiscaceae evolved from marine thalassiosiroid ancestors that invaded high latitude lacustrine environments during multiple Paleogene highstands, resulting in a polyphyletic origin of the family. The turnover from nonmarine Actinocyclus to Stephanodiscaceae genera near the middle/late Miocene boundary may be linked to a contemporaneous increase in silica concentrations in lakes caused by active volcanism, increased weathering of silicate rocks due to orogeny, and the expansion of C4 grasslands. This turnover may also have been influenced by enhanced seasonal environmental changes in the euphotic zone caused by the initiation of monsoon conditions and a worldwide increase in meridional temperature gradients during the late Miocene. Morphological characteristics of Stephanodiscaceae genera, such as strutted processes and small size, suggest their species were better adapted to seasonal environmental changes than nonmarine species of Actinocyclus because of their superiority in floating and drifting capabilities and possibly metabolism, intrinsic growth rate, and reproductivity. As climates deteriorated during the late Miocene, Stephanodiscaceae species may have spread from high latitudes to temperate lakes where they diversified, ultimately displacing Actinocyclus..
2. Tatsuya Hayashi, Yoshihiro Tanimura, Morphological variability of Cyclostephanos ramosus sp. nov. from Pleistocene sediments of the Paleo-Kathmandu Lake, Nepal, Diatom, 31, 1-11, 2015.12, [URL], A new diatom species, Cyclostephanos ramosus sp. nov., is described from Pleistocene sediments of the Paleo-Kathmandu Lake, Nepal. Cyclostephanos ramosus is a polymorphic species characterized by three morphological variations, which are related to valve silicification, valve size and stratigraphic distribution. Heavily-silicified valves exhibit an annulus and network-like structures in the valve center and narrow secondary costae in the mantle area. Other valves have a variable number of valve face areolae, mantle areolae, costae, and mantle fultoportulae, and show differences in the shape of the mantle costae. The number of costae and mantle fultoportulae also shows variations related to stratigraphic distribution, which occur on a time scale of a few tens of thousands of years. On the basis of morphological characteristic features, C. ramosus is most similar to Cyclostephanos malawiensis, but differs in its domed cribra on the mantle, much deeper mantle and larger distance between spines and mantle fultoportulae. The three morphological variations have different implications. Valves showing variation in silicification reflect an eco-morphological response to available silica, while valves with size-related variations show morphological modification brought about by vegetative cell divisions. The stratigraphic variations are highly suggestive because they indicate that the number and shape of costae, which have been traditionally used to delineate Cyclostephanos species, can vary intraspecifically on long time scales. These facts suggest the careful examination of intraspecific morphological variations on various time scales is required for the taxonomy of Cyclostephanos..
3. Tatsuya Hayashi, Monospecific planktonic diatom assemblages in the Paleo-Kathmandu Lake during the middle Brunhes Chron: implications for the paradox of the plankton, Palaeogeography, Palaeoclimatology, Palaeoecology, 10.1016/j.palaeo.2010.12.007, 300, 1-4, 46-58, 2011.02.
4. Tatsuya Hayashi, Masao Ohno, Gary Acton, Yohan Guyodo, Helen F. Evans, Toshiya Kanamatsu, Fumiki Komatsu, Fumi Murakami, Millennial-scale iceberg surges after intensification of Northern Hemisphere glaciation, Geochemistry, Geophysics, Geosystems, 10.1029/2010GC003132, 11, 9, 2010.09.
Membership in Academic Society
  • Paleosciences Society
  • Geological Society of Japan
  • Palaeontological Society of Japan
  • International Society for Diatom Research
  • Japanese Society of Diatomology
  • Japan Association for Quaternary Research
Educational
Other Educational Activities
  • 2019.04.
  • 2019.03.
  • 2018.08.
  • 2018.02.