黄土高原现代天然降尘的组成、通量和磁化率

Composition, Susceptibility and Input Flux of Present Aeolian Dust Over Loess Plateau of China

黄土高原现代天然降尘的季节性变化研究表明 ,矿物粉尘是天然粉尘的主要组成成分 ,有机质和污染物以夏季粉尘中含量最高。粉尘的磁化率在 80～ 1 50单位之间 ,明显高于冰期黄土 ,指示着间冰期时原始粉尘的磁化率就已受到气候条件的影响。粉尘沉积通量的季节性变化在高原北部较大 ,中部和南部变化较小 ,年累积通量也是北部明显高于基本相当的其它地区。分析粉尘沉积的气候过程认为 ,黄土高原的天然降尘主要表现为常态存在的非尘暴降尘 ,大部分为近距离低空再搬运粉尘 ,其沉积通量与地表的干燥度密切相关 ,部分来自内陆远源沙漠 ,通过高空西风气流转输。冬季风粉尘在大部分黄土高原略高于其它季节粉尘 ,而在西北部显著增高。

Present aeolian dust is collected at 7 sites in different parts of the Loess Plateau of China. Investigation on the composition indicates that mineral dust makes up the dominant part of the dust. Magnetic susceptibility of the dust varies in range of 80~150 units (10 -8 m 3/kg), which is higher than that of glacial loess. The high susceptibility of present dust implies that original material of dust has been modified to certain extent by climatic condition. Seasonal variability of dust input flux exhibits a gentle decrease from northwest to southeast with strong seasonal variety in the northern margin of the Loess Plateau. Accumulated input flux of the dust remains consistent over most regions except for northern part where possesses obvious high input flux. Meteorological analysis on transportation and deposition process reveals that most dust material is produced in non storm deposition rather than in dust storm deposition. Aeolian dust is mainly transported by low level winds in step wise way to deposit in destination sites, and therefore its input flux offers an indicator to ground aridity of depositional as well as the source areas. Long suspension dust from desert regions plays an important role in fine port of the aeolian dust. Compared to the other seasons, dust flux resulted from winter monsoon rises obviously in the northwestern part of the Loess Plateau, whereas other parts possess limited increase of dust input.