【摘要】 通过对冲绳海槽北部沉积物柱状样S9进行AMS¹⁴C测年和粒度分析,获取了全新世以来高分辨率的古环境演化记录。结果显示,千年尺度上,S9柱粒度组成呈现明显的两段式变化特征:10.5⁸.0ka B.P.,平均粒径逐渐变粗并达到最高值,粉砂含量逐渐增加并达到最高值;8.0¹.0ka B.P.,沉积物平均粒径呈现递减的趋势,粘土含量相对增加。S9柱粒度千年尺度上变化与区域海平面变化密切相关,显示了海平面对区域物质输运的控制作用。7.5ka B.P.以来,海平面趋于稳定,粒度特征呈现出百年尺度上波动。S9柱粒度变化参数与源区指示季风降雨量石笋记录的δ¹⁸O具有良好的相关性,7.5ka B.P.以来持续减小的平均粒径对应持续减弱的区域夏季风降雨。此外,S9柱记录了约8.2ka B.P.,6.5ka B.P.,4.2ka B.P.以及3.8ka B.P.等多期粒度显著变细的百年尺度的气候事件,对应了区域季风降雨的减少时期。S9柱粒度组成信息揭示了全新世以来区域海平面变化及季风降雨的强弱对冲绳海槽沉积物组成的影响,同时也为利用海洋沉积物来重建区域季风降雨提供了有力的手段。更多还原

【Abstract】 High resolution paleoenvironmental records since Holocene have been acquired by the AMS ¹⁴C age-testing and grain size analyzing of the Core S9 sediments（29°23.4989’N,128°15.8230’E）,which was taken from the northern Okinawa Trough with 251 cm length and 1062 m water depth during the Okinawa Trough Cruise in the summer of 2013.A total of 251 samples were collected from the Core S9 at 1cm intervals.Because of the agglomeration in the bottom of the sediments,226 samples were used for particle size measurement by Cilas 940 L Laser particle size instrument in the Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences.A high-resolution age model of the core was established on five samples（30cm,80 cm,165cm,220 cm and 243cm） on the basis of accelerator mass spectrometry（AMS） radiocarbon dating of planktonic foraminifera（Globigerinoides ruber,Globigerinoides sacculife,Pulleriatina obliquilocalata,Neogloboquadrina dutertrei,and Globigerina bulloides） which were measured at Woods Hole Oceanographic Institution.The depositional age is estimated to be 13.39 ka at the bottom of the core and 1.1ka at the top of the core.The sedimentation rate of the core is 8cm/ka during the Early Holocene and increases from 17cm/ka to27cm/ka during the Middle Holocene and increase to 32cm/ka during the Late Holocene.Sediments from the Core S9 are primarily composed of silt（60%⁹0%）,with a mean grain size of 5.6⁷.2φ and a median grain size of5.2⁷.2φ.A tephra layer in the Core S9（159 169cm） correlates well with the volcanic eruptions at 7.3ka in Southern Japan.The results reveal that the grain size composition of the Core S9 present two-stage obvious variation in millennial scales;the mean and silt increase and reach the maximum in 10.5⁸.0ka B.P.,and the mean and clay decrease in 8.0 1.0ka B.P.The changes of grain size of Core S9 are related with the relative sea-level changes,implying the control of the relative sea-level on regional material transport.The relative sea-level has been stable since 7.5a B.P.and the grain size varies in century scales and is controlled by regional monsoon rainfall in the source region.The grain size parameters of the Core S9 are well correlated with the stalagmite records of δ¹⁸O in the source region.The mean has been decreased since 7.5ka B.P.,showing well consistency with the regional summer monsoon rainfall.Moreover,the Core S9 records reveal several climate events in century scales,such as ca.8.2ka B.P.,6.5 ka B.P.,4.2ka B.P.and 3.8ka B.P.,which the grain size decreases obviously,and they are corresponding to the periods when regional monsoon decrease.The grain size composition of the Core S9 implies the influence of the relative sea-level changes and regional monsoon rainfall in the source region to the sediments composition in the Okinawa Trough,and provides a powerful tool to use marine sediments features to rebuild regional monsoon rainfall.更多还原