2008 年 114 巻 1 号 p. 47-50
Neodenticula kamtschatica (Zabelina) Akiba and Yanagisawa, an extinct late Neogene planktonic diatom has been very first observed in the middle Quaternary submarine deposit in the northeastern North Atlantic. The species has been considered for a long time to be limited within the high-to-middle latitudinal North Pacific. In the North Pacific region, this species appeared in the geologic record approx. at 6.4 Ma as “first common occurrence”, and became extinct at 2.65 Ma occurrence. On the other hand, no record of the Atlantic specimens has been presented. Thus, its fossil imprint in the North Atlantic of our investigation implies that at least single episode of the trans-ocean migration (=floral interchange of North Pacific and North Atlantic via the Arctic) of the species occurred during the latest Miocene through Pliocene epoch, considering the tectonic and hydrographic backgrounds such as the initial opening of the Bering Strait (5.5 Ma~) and the final closure of the Panamanian Isthmus (~2.76 Ma). Our evidence is significant to give a further insight on the relationship between the process to establish biogeography of planktonic micro-organisms and the paleoenvironmental change in the Northtern Hemisphere.