Late Cenozoic paleoceanographic changes in the adjacent seas of the Ryukyu Islands.

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1. Piston core [KT84-14-Pl] collected from the trench slope east off the Miyako Islands at the water depth of about 2,200 m: This 416 a long core has recorded many paleoceanographic conditions during the past 150,000 years, judging from analyses of benthic foraminiferal faunas, calcareous nannoplankton floras, oxygen and carbon stable isotopes of planktonic and benthic foraminiferal tests, chemical compositions (particularly carbonate) , and two ash layers. A manuscript of this synthetic study is prepared for submitting to the journal, Marine Micropaleontology. A monograph described 163 taxs (three new genera and 10 new species included) of benthic foraminifera from the core was published in early 1990.2. Piston core [RN87-PC4] collected from the trench slope south off the Ishigaki Islands at the water depth of 2,488 m: It is verified that this 356 cm long care attains to about 90,000 years ago by an ash layer and calcareous nannoplanktons. Benthic foraminiferal change against the glac … More iation change is less responsible than the case of KT84-14-P1, probably because of more southerly location of this core.3. Piston core [RN89-PC3] collected from the trench slope southeast off the Kerama Gap at the water depth of 2,486 m: This telescopic core (386 cm long) seems to have recorded the paleoceanographic situation for the past about 370,000 years based on three fold evidences; oxygen isotope measurements of planktonic foraminifera, calcareous nanno-plankton stratigraphy, and an ash layer. Planktonic foraminiferal delta^<18> has changed in response to glaciation change, although more delicate fluctuation is not observed in comparison with KT84-14-P1. Benthic foraminiferal fauna also similar responsibility and the major component taxa occur rather continuously through the core differing from the case of KT84-14-P1.4. The Shimajiri Group, which is broadly developed in the southern part of the Okinawa Islands, has been regarded as the trench slope sediments during the period from 7 Ma to 1.7 Ma. According to preliminary study of its benthic foraminifera, however, it is suggested that the trench slope condition differs from that of the present day or the latest Quaternary period. Less