沖縄トラフおよび石垣島南方で採取されたIMAGESコアに基づく過去約25万年間の表層・中層水の変動(<特集>西太平洋におけるIMAGESコアを用いた高時間解像度の環境復元)

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Two IMAGES cores MD98-2196 (the Okinawa Trough side) and MD01-2398 (the Ryukyu Trench side) present a 250 kyr precise record of the oceanic environment in the Ryukyu Arc region, where is a key area for the Kuroshio Current of the subtropical circulation in the North Pacific Ocean. Here we reconstruct the changes in the surface and intermediate waters across the past two glacial cycles, based on planktonic and benthic foraminiferal assemblages. During the deglacial and interglacial periods (MIS: Marine Isotope Stage 1, 5, 7), a distinct influence of warm surface water is recognized by high abundances of tropical/subtropical water species at both core sites. Especially, the abundance of Pulleniatina group, the dominant species of the Kuroshio water, increases in the Okinawa Trough for those periods according with global warming, suggested by planktonic δ^<18>O and sea surface temperature (SST) records. Interglacial hydrographic conditions are similar to today's condition of the Ryukyu Arc region, as supported by not only planktonic but also benthic foraminiferal assemblages. On the other hand, cold water occupies this region during the glacial periods (MIS 2-4, 6). Especially, these glacial hydrographic changes are affected until the bottom layer in the Okinawa Trough, as estimated by benthic foraminiferal assemblages. The high abundance of Neogloboquadrina pachyderma demonstrates the development of cold water mass during MIS 2, particularly in the Okinawa Trough, whereas Turbolotalia inflata is more dominant than N. pachyderma during MIS 6, indicating strong influence of the western Pacific Central water mass over this region. The highest abundance of T. inflata between ca. 180 and 150 ka occurs simultaneously with the formation of a thick mixed layer in the east equatorial Pacific Ocean relatimg with the advection of an intermediate water ventilated from the polar area. It may indicate the global change in the intermediate water, though we do not find a significant relationship between North Pacific Intermediate Water (NPIW) and Sub-Antarctic Mode Water or Antarctic Intermediate Water (SAMW/AAIW) in the northwestern Pacific. Moreover, at the onset of Termination II (MIS 5/6), very strong upwelling intensity in the surface water is suggested by the abrupt increase of Globigerina bulloides only in the Okinawa Trough, according with the rising of the intermediate water represented as the spikes of its benthic environmental component at the Ryukyu Trench slope. From MIS 6 to Termination II, the intermediate water may become strong and provide high nutrient water to the marginal area responding to the development of winter monsoon, one of main producers for NPIW.
日本古生物学会の論文
2006-03-28

沖縄トラフおよび石垣島南方で採取されたIMAGESコアに基づく過去約25万年間の表層・中層水の変動(<特集>西太平洋におけるIMAGESコアを用いた高時間解像度の環境復元)

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