Paleohydrography of the Kuroshio-Kuroshio Extension based on fossil diatoms

Abstract

The hydrographic history of the Kuroshio-Kuroshio Extension system east off Honshu during 200 thousand years was reconstructed based on high-resolution records of fossil diatoms in three cores recovered from the area beneath the Kuroshio Warm Core. The influences of the terrestrial environments are implicated in the fluctuations in number of diatom valves, and in relative abundances of extinct, freshwater and littoral diatom species; in the Kuroshio Extension off shore area extinct, freshwater and littoral diatoms showed decrease in their relative abundance. The Earth's orbital parameters and the variations in isostatic balance in the Northern Hemisphere are considered to have controlled the species composition of diatom flora. The warm-water diatom species in littoral-neritic association are predominant in the near shore area due to the Kuroshio flowing northeast along the coast of southwest Japan. The cold-water species of oceanic association are predominant in the Kuroshio Extension off shore, where southward Oyashio flows in from the Bering and Okhotsk Seas.