Paleoceanographic implications of a 90,000 year long diatom record in piston core KH94-3, LM-8 off NE Japan

Q-mode principal component analysis (PCA) of a fossil diatom assemblage rev eals the late Quaternary paleoceanography of the NW Pacific margin, based o n submarine core KH94-3, LM-8 recovered off the Sanriku coast of NE Japan ( 38 degrees 53.36 'N, 143 degrees 22.19 'E). Overall, diatoms were abundant during interglacials, but low in abundance and poor in preservation during the last glacial, with each oxygen isotope stage having its own characteris tic assemblage. The results of PCA are: principal component 1 (PC1) is comp osed mainly of Thalassionema nitzschioides, which predominated during the c oldest oxygen isotopic Stages 4 (75-58 ka) and 2 (25-11 ka), and by allocht honous taxa. The diatom tests are poorly preserved and the diatom mass accu mulation rate (DMAR) is the lowest in these stages. PC2 is characterized by ice-related diatoms that predominate in Stage 3 (the interstadial), wherea s PC3, which is characterized by Neodenticula seminae and Odontella aurita, shows high values in Stage 1. Diatom assemblages exhibit drastic changes b etween oxygen isotopic Stages 3 and 1 (11-0 ka). Distinct increases of DMAR occurred during both periods. We infer an intensified advection of sea ice from the Sea of Okhotsk toward the area off Sanriku during Stage 3. This interpretation explains the high DMAR in Stage 3, owing to high productivity at the sea ice edge. Our study can contribute to marine environmental reconstruction since the last glaci ation because fewer micropaleontological data exist in the NW Pacific margi n for these time intervals, compared with other oceans. (C) 2001 Elsevier S cience B.V. All rights reserved.