The Palynological Assembled And Its Significance Of Paleoclimate In The Center And North Part In Okinawa Trough During The Last Glaciation

Based on the analysis of palynological assemblage in the piston core CSH1, DOC024 and Y179, combined with other methods such as oxygen and carbon isotopic compositions of foraminifer and AMS14C analysis results, the history of vegetation and climate variation in the middle-north part of Okinowa Trough were reconstructed in this paper.The shape of spore-pollen curves of piston core CSH1 makes it possible to subdivide the succession into different time intervals from bottom to top: Period I (34~61kaB.P. )is the prosperous period of TorMC, when pinus and semitropical alpine aiphyllus coniferous forest flourished. The derived palynological assemblage suggests that the palaeoclimate during that period was arid and warm. Period II (7.7-34 kaB.P.) is a prosperous period of xerolphitic herbage, when Artemisia plants prospers, which suggests the climate was xeric and large-scale marine regression may had occurred.Periodlll (0—7.7kaB.P.) is the prosperous period for evergreen latifoliate forest, the decilious broadleaved forest increased, the relative abundance of ferns spore reached the maximum while herbs decreased rapidly, which suggests it was warm and humid. The percentage of Herbs, Trees and Shrubs pollen during Period I and Period II was higher than that during Periodlll, as a conquence of correlating the curve of Herbs, Trees and Shrubs pollen with that of 8 I8Oof GISP2,a spectrum of climate variations and abrupt paleoclimate events corresponding to YD,H1,H2,H3,H4 and H5 respectively could be recognized.The shape of spore-pollen curves of piston core DOC024 can be divided into four assemblage zones: Period I (7500-6600kaB.P): the palaeoclimate during this period was cold and humid; Period II (a)(4900-3100kaB.P.) is the prosperous period for semitropical vegetation, suggests the climate was warm; Period II (b)(4900-3100kaB.P.):the temperature during this period has no obvious changes but the humidity receded; Period 111(3100-1500kaB.P.):the pollen content of extratropical vegetation increased but that of tropical-semitropical vegetations decreased, suggests a drop of temperature; Period IV(1500-200kaB.P.):it is the prospers period for fern, the climate risen during this period andthere was a temperature downtrend after 300kaB.R. The shape of δ 18O curve was studied in this paper, it shows that the changing character of δ 18O curve has coincidence relations to that of Spore-pollen assemblage.The shape of spore-pollen curves of piston core Y179 can be divided into four palynogical assemblage zones from bottom to top: Period I (12000-7200kaB.P.) is a prosperous period of herbage, suggests the climate was xeric, large-scale marine regression may have occurred and a wide range of continent shelf may have broken surface;the palaeoclimate during this period was cold and humid; Period II (7200-5000kaB.P.) is the prosperous period for tropical vegetation while a extinctive period for extratropical vegetation and herbage, suggests the climate was warm and the sea level may have raised in this period; Period III (5000-2800kaB.P.):the pollen contents of extratropical vegetation increased but those of tropical-semitropical vegetations decreased, suggests a drop of temperature in this period; Period IV (2800-100 kaB.P.):the pollen contents of extratropical vegetation decreased while those of tropical-semitropical vegetations increased, the pollen of chenopodiaceae and ephedraceae appeared, suggests the climates was arid and warm.During 7900aB.P.-5900 aB.P. the presence of Phyllocladus pollen had appeared, suggests kuroshio had entered Okinowa Trough and its intensity had been enhanced.