Q-mode principal component analysis (PCA) of a fossil diatom assemblage reveals the late Quaternary paleoceanography of the NW Pacific margin, based on submarine core KH94-3, LM-8 recovered off the Sanriku coast of NE Japan (38 o 53.46'N, 143 o 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 characteristic assemblage. The results of PCA are: principal component 1 (PC1) is composed mainly of Thalassionema nitzschioides, which predominated during the coldest oxygen isotopic Stages 4 (75-58ka) and 2 (25-11ka), and by allochthonous taxa. The diatom tests are poorly preserved and the diatom mass accumulation rate (DMAR) is the lowest in these stages. PC2 is characterized by ice-related diatoms that predominate in Stage 3 (the interstadial), whereas PC3, which is characterized by Neodenticula seminae and Odontella aurita, shows high values in Stage 1. Diatom assemblages exhibit drastic changes between oxygen isotopic Stages 3 and 1 (11-0ka). 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 glaciation because fewer micropaleontological data exist in the NW Pacific margin for these time intervals, compared with other oceans.