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Variations in fossil diatom assemblages and their relationship with global and Indian monsoon climate changes for the last 600,000 yr were investigated using a core of ancient lake (Paleo-Kathmandu Lake) sediments drilled at the Kathmandu Basin, Nepal Himalaya. Chronological scales of the core were constructed by tuning pollen wet and dry index records to the SPECMAP δ18O stack record. Examinations of biogenic silica contents and fossil diatom assemblages revealed that variations in productivity and compositions of diatom assemblages were closely linked with global and Indian monsoon climate changes on glacial and interglacial time scales. When summer monsoonal rainfall increased during interglacials (interstadials), diatom productivity increased because of increased inputs of terrestrial nutrients into the lake. When summer monsoonal rainfall reduced and/or winter monsoonal aridification enhanced during glacials (stadials), productivity of the diatoms decreased and lake-level falling brought about changes in compositions of diatom assemblages. Monospecific assemblages by unique Cyclotella kathmanduensis and Puncticulata versiformis appeared during about 590 to 390 ka. This might be attributed to evolutionary fine-tuning of diatom assemblages to specific lake environmental conditions. Additionally, low-amplitude precessional variations in monsoon climate and less lake-level changes may have also allowed both species to dominate over the long periods.

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The 8 and 27 keV monoenergetic neutron calibration fields have been developed by using (45)Sc(p, n)(45)Ti reaction. Protons from a 4-MV Pelletron accelerator are used to bombard a thin scandium target evaporated onto a platinum disc. The proton energies are finely adjusted to the resonance to generate the 8 and 27 keV neutrons by applying a high voltage to the target assemblies. The neutron energies were measured using the time-of-flight method with a lithium glass scintillation detector. The neutron fluences at a calibration point located at 50 cm from the target were evaluated using Bonner spheres. A long counter was placed at 2.2 m from the target and at 60 degrees to the direction of the proton beam in order to monitor the fluence at the calibration point. Fluence and dose equivalent rates at the calibration point are sufficient to calibrate many types of the neutron survey metres.

Diatom analysis of two submarine cores off eastern Hokkaido Island, northern Japan, provides insights into the Holocene palaeoenvironmental history of the southwestern Okhotsk Sea. Diatom flora was mainly composed of open-water and/or high-productivity-related Thtalassionema nitzschioides, Neodenticula semninae and sea-ice-related species such as Bacterosira fragilis and Fragilariopsis cylindrus, suggesting millennial-scale alternation of dominant hydrographic regimes. Great abundances of T. nitzschioides and N. seminae, in particular, together with the ice-related species, from the early Holocene onward show that this biota was the major contributor to productivity in the southwestern Okhotsk Sea. On the other hand, faint but important occurrences of warm-water species such as Fragilariopsis doliolus were observed during 6.3-5.5, 4.2-2.7 and 1. l-0.2 ka. Such rhythmic occurrences of warm-water species as a sensitive indicator of the Soya Warm Current and the terminal branch of the subtropical Kuroshio Current reflect this history. The presence of this warm species is probably in tune with pulses of the Tsushima Warm Current that have been documented in Holocene sediments of the Japan Sea. These floral results, which might imply the millennially paced variability in palaeoclimate regimes in both Subarctic and subtropical regions, are well documented in these cores from the southwestem Okhotsk Sea.

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