Neogloboquadrina pachydermaとNeogloboquadrina incomptaの古海洋学的意義(<特集>後期新生代の環境指標としての微古生物学と古海洋学の進展)

概要

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Neogoboquadrina group is dominant in modern planktic foraminiferal assemblages around Japan. As on of the most useful paleoceanographic proxies, the coiling direction of Neogloboquadrina pachyderma was widely used by many workers who have explained the behavior by temperature controlling the coiling direction in a single species. Morphologic characteristics and geographical distribution pattern, however, reflect the presence of two distinct species with opposite coiling direction preferences in the Northwest Pacific and Japan Sea. The Oyashio and cold waters in Japan Sea are inhabited by N. pachyderma, with dominantly sinistral shells associated with rarely dextral forms. On the other hand, the dominantly dextrally coiled Neogloboquadrina incompta, accompanied with rarely sinistral shells, thrives in (1) the Perturbed area located between the Oyashio and the Kuroshio fronts and (2) the transitional water formed by mixing of the Tsushima Warm Current with cold waters in Japan Sea. In addition, N. incompta is also common in the area off Ensyu-nada, where the cold water mass occurs associated with the meandering of the Kuroshio. Thus, N. pachyderma and N. incompta are the optimal markers of the cold waters and the transitional waters as well as the cold water mass in the Kuroshio domain, respectively. These two species contribute to reconstruct the paleoceanography in Northwest Pacific and Japan Sea.
2009-10-16