对菲律宾海西北部奄美三角盆地U1438A孔约350 ka以来沉积物中碎屑组分的粒度组成进行了分析,结果表明,沉积物中碎屑组分的平均粒径为13.1 μm,粒径变化范围为0.04~160 μm,粒度频率分布呈四峰正偏态分布。利用Weibull分布函数将沉积物碎屑组分的粒度组成分离出4个相对独立的组分。其中超细组分众数约0.3 μm,粒度分布范围为0.04~0.9 μm,可能是海洋自生黏土。细粒端元众数粒径约3.5 μm,粒度分布范围为0.2~32 μm,比北太平洋中部风尘略粗,推测主要为来源于亚洲大陆的风尘。粗粒端元众数粒径约10 μm,粒度分布范围为0.3~90 μm;超粗粒端元众数粒径约40 μm,粒度分布范围为3~160 μm。粗粒组分和超粗粒组分均主要来自于周围海脊和岛弧的火山物质。细粒和粗粒敏感粒级组分的比值(1.3~2.2 μm/28~40 μm)与细粒风尘组分和粗粒火山组分的比值(0.9~3 μm/>10 μm)类似,表现为冰期高、间冰期低,与北太平洋风尘通量、亚洲大陆黄土堆积速率,以及黄土粒径所指示的冰期干旱和东亚季风/西风环流增强的气候变化是一致的,表明冰期由于亚洲大陆的干旱和季风/西风的增强,使得奄美三角盆地中细粒亚洲风尘组分的输入相对增加。因此细粒风尘和粗粒火山物质的比值可以作为亚洲大陆干旱化和大气环流增强的示踪指标。这些研究结果表明奄美三角盆地沉积物的粒度组成可用于重建东亚大陆干旱和大气环流演化历史。

The grain size composition of detrital sediments in Hole U1438A from the Amami Sankaku Basin(ASB) in the northwest of the Philippine Sea since the last 350 ka was analyzed. The result shows that the mean grain size of the detrital sediment is about 13.1 μm, ranging from 0.04 to 160 μm. The grain size distribution displays a four-peak pattern and positive skewness. Four independent grain size components were separated by using Weibull distribution function. The ultra-fine component varies from 0.04 to 0.9 μm, with a size mode at about 0.3 μm, which may be genetically related to marine authigenetic clay. The fine-grained fraction ranges from 0.2 to 32 μm, with a size mode at about 3.5 μm, and slightly coarser than the eolian dust of the North Pacific. We argued that this fraction was mainly derived from Asian dust. The coarse-grained and ultra-coarse-grained fractions show distinct size mode at about 10 μm and 40 μm, and range from 0.3 to 90 μm, and from 3 to 160 μm respectively. Both the coarse and ultra-coarse components represent volcanic materials which were mainly derived from the ridges and islands around ASB. The variation of the ratio of environmentally sensitive size population 1.3~2.2 μm/28~40 μm was similar with the ratio of fine-sized component (Asian dust) and coarse-sized component (volcanic material) (0.9~3 μm/>10 μm), showing higher value during glacial period than that during interglacial, which is also identical with the variation of the mass accumulation of eolian dust in the North Pacific and Chinese Loess Plateau, and grain size in Chinese Loess Plateau. The increased ratio responded to the enhanced aridity of Asian continent and strengthened East Asia Winter Monsoon (EAWM)/westerly during glacial period. We argued that the increase of eolian fraction was driven by the enhanced aridity of Asian continent and strengthened East Asia Winter Monsoon (EAWM)/westerly during glacial period. Therefore, the ratio of 0.9~3 μm/>10 μm can be used as a proxy of the increased aridity and enhanced atmospheric circulation of Asian continent. These results suggest that the grain size composition of the detrial sediment in the ASB can be used to reconstruct the history of Asian aridity and atmospheric circulation.