房総半島・金華山沖の浮遊性有孔虫群

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  • Planktonic Foraminifera off the Coast of Boso Peninsula and Kinkazan, Japan
  • ボウソウ ハントウ キン カザンオキ ノ フユウセイユウコウチュウグン

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Foraminifera assemblages have been analyzed from 17 vertical plankton tows taken along two traverses, off Boso Peninsula and Kinkazan. Locations of stations are shown in Figure 1 and are listed in Table 1 together with dates, times of collections. Type of plankton net used is the Kitahara sampler which has a mouth diameter of 24 cm. and is made of no. XX13 silk grit gauze with effective apertures of 0.1mm.<BR>Total Foraminifera population of each sample and frequency (in %) distribution of each species are listed in Table 2. Stations with asteric (*) mark indicate that calcareous tests of Foraminifera were dissolved and only light greenish protoplasms were present when examined. Sample B1 contains an extraordinally large population of diatom and also a large population of Foraminifera. Excluding sample B1 and six samples in which the calcareous tests were dissolved, Foraminifera population gradually increases from nearshore towards offshore reaching maximum at stations K3, B3 and B3', and then decreases farther offshore. The decrease of the population towards offshore may be related to a small gyre of the Kuroshio. The maximum populations appear to be related to the main course of the Kuroshio, or to the collections during the daytime (from ca. 10 a.m. to ca. 2 p.m.). Diurnal vertical migration of planktonic Foraminifera, that is, larger population in the daytime and smaller population at night near the sea surface, is known in the Central Pacific and an interpretation is given by BRADSHAW.<BR>No cold water species is found, which suggests that the warm Kuroshio covered this area when sampled. Globigerina eggeri and Globigerinoides rubra are dominant species, and the latter reaches its maximum frequency along the main course of the Kuroshio. The other species, except Globigerina bulloides, are tropical or subtropical species but occupy small percents.<BR>Seasonal change of distribution of Foraminifera along a traverse south of Boso Peninsula is not clear because of the dissolution of the calcareous tests, yet it shows some tendencies, that is, maximum population at B3 and B3', absence of Globigerina eggeri and dominance of Globigerinoides rubra in spite of rather marked difference in water temperatures at the times of collections.

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