中国帕米尔地区黄土上部色度变化特征及古气候意义

Chroma Characteristics and Its Paleoclimatic Significance in Pamir Loess Section,China

以中国境内帕米尔黄土—古土壤序列为研究对象,对剖面上部进行土壤色度指标与其他常用气候替代指标(如磁化率、碳酸盐和有机碳)对比研究后发现:在帕米尔黄土沉积期间,亮度L*很大程度上受控于颜色分量a*和b*,进而可能与影响a*、b*的物质相对含量有关。红度a*在整个黄土—古土壤剖面中变化特征明显,与磁化率呈明显的负相关关系,可能与土壤中铁氧化物的种类和含量关系密切。由于a*和b*具有较高的相关性,认为它们具有较为一致的致色物质,可能受控于相似的气候因子。色度a*、b*和亮度L*的变化表明其可以作为帕米尔地区良好的气候代用指标,结合磁化率共同反映该地区的古气候变化过程。

Loess is one of the most detailed terrestrial widespread high resolution archives of climate and environment change,the study of the loess-paleosol sequences in Pamir allows one to assess the changes in the environment and pedogenesis over the interglacial and glacial epoch of the Quaternary period.However,deciphering such amount information requires multi-proxy to investigate the temporal process of aeolian dust and paleoclimate,which is important for understanding the forcing mechanisms of past climate in Pamir region and also for predicting the future regional climate changes under the global warming background.Soil color,one of the sensitive proxies for paleoclimate,has been widely used as an indicator of chemical and biological properties as well as the soil-forming process in the loess study.In view of above analysis,combined with magnetic susceptibility,calcium carbonate and organic matter proxies,this paper measured the chromatic proxies to investigate the spatial and temporal variations of soil color and their major controlling factors at the Pamir loess section dominated by westerlies.The results show that the introduction of chroma could compensate for defects in paleoclimate reconstruction when magnetic susceptibility cannot record the process of climate change and soil development well.In the process of loess accumulation,lightness L*,to a large extent,was dominated by color components a*and b*,furthermore,may be correlated to the substance that affect color component a*,b*.Redness a*and yellowness b*were controlled by the similar climatic factors and might process the consistent color material because of their relatively high correlation.Largely influenced by the categories and contents of iron oxide and correspond well with magnetic susceptibility,Redness a*could indirectly reflect the climate change and pedogenic environment in this region.The relationship between chromatic proxies and magnetic susceptibility indicate that magnetic susceptibility and a*show a positive correlation,for L*it is a negative one;this is due to the fact that their dominating matter is different.Only the combination between chromatic proxies and other climatic proxies,could we reconstruct a reasonable and reliable process of climate change in the Pamir region.