Revising the Miocene through Pleistocene diatom biostratigraphy on the drill cores recovered in DSDP Leg 19 results in the dating of Neogene sequences especially for Sites 183 and 192 in the far North Pacific Ocean. Ages for the basal part of the lithologic unit A (opal-A), diatom ooze to diatomaceous mud, overlying the unit B (opal-CT), mudstone with no diatom, are older than 10 Ma at 210 mbsf in Site 183, about 9.5 Ma at 718 mbsf in Site 192, and about 4.6 Ma at 582 mbsf in Site 188, at 370 mbsf in Site 187, at 587 mbsf in Site 185 and at 599 mbsf in Site 184, and about 3.2 Ma at 521 mbsf in Site 191, at 618 mbsf in Site 190, at 541 mbsf in Site 189 and at 926 mbsf in Site 186. The diagenetic boundary between opal-A and opal-CT distinctively forms a diachronic plane in the subarctic Pacific. Fossil diatoms in the dredged samples from the Bering Sea indicate stratigraphically major increasing times of diatom mass accumulation rates in the North Pacific: 10-9 Ma, 7-6 Ma, and 3-2 Ma.

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The crewed submersibles and ROVs of JAMSTEC have obtained many images of nektonic cephalopods, but they only rarely catch voucher specimens of such fast-moving animals. An inventory of JAMSTEC's cephalopod specimens collected by those vehicles yielded nineteen species including some noteworthy species.

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Two types of handcorers with different internal diameters (MBARI type corer [MC] ; 7cm, KITAZATO type corer [KC] ; 8cm) were evaluated for their sampling efficiency and sampler bias on meiofauna, based on the samples collected with these corers during dives #820 ∼ 822 of ROV “Hyper Dolphin” at Myojin Knoll, which is about 150km south-southwest of Hachijo Island. It was suggested that the sampling efficiency became worse when overlying water above sediment is leaked from the core samples, regardless of corer type. Meiofauna in the sediments collected with KC showed the “general” vertical distribution pattern; meiofauna were concentrated in the surface layer of the sediments. On the other hand, in the sediments collected with MC, the vertical profiles of meiofauna were rather “uniform”. Furthermore, the community compositions at higher taxonomic level were different from those in the sediments collected with KC. These differences between the corers would be attributed to the differences in core diameter and the degree of disturbance to the edge and surface of the sediment samples. Handcorer-sampling with ROVs or submersibles is essential to the studies on meiofauna around hydrothermal vents. These results of this study, however, suggest that comparing meiofaunal data based on samples collected with different types of handcorers should be done carefully.

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