中文摘要：

磁化率是黄土-古土壤序列古气候研究的一个重要指标。本文调查了黄土高原及周边地区三种类型土壤的磁化率、土壤有机碳含量、有机碳同位素组成和碳氮比值等指标。样品采集自黄土-沙漠过渡区、黄土塬面和森林地区,代表了黄土高原地区主要的土壤类型。结果显示：黄土塬面、林区、黄土-沙漠过渡区土壤的磁化率变化区间分别为26.6×10^-8—61.4×10~（-8） m^3·kg^-1、68.6×10^-8—107.5×10^-8 m^3·kg^-1、8.5×10^-8—44.4×10^-8 m^3·kg^-1。黄土塬面土壤有机碳含量在0.05%到0.62%之间变化,而林区土壤的有机碳含量在1.19%到3.35%间变化。黄土塬面的土壤C/N比值也较低,在0.6到6.1之间变化,林区样品C/N比值在6.2到11.83之间变化。黄土-沙漠过渡区土壤磁化率较低,森林地区土壤磁化率较高,土壤磁化率与有机碳含量、C/N比值呈正相关关系。笔者认为有机质含量增加对土壤的磁化率增强有明显贡献。有机质含量较高时,更适宜土壤中磁性细菌的生长。同时,较高的有机质含量指示着较高植被覆盖,这也对土壤中磁性矿物增加有一定贡献。燃烧有机质还会使非磁性矿物更易转化为磁性矿物。这些因素都会增强土壤的磁化率。

英文摘要：

Background, aim, and scope Magnetic susceptibility of soils can provide paleoclimatic information. In Chinese Loess Plateau, susceptibility enhancement is usually considered as a proxy of monsoon intensity. Several hypotheses were used to explain variations of this proxy. Here, we present a study on how soil magnetic susceptibility is related with soil organic matters. We analyzed magnetic susceptibility, organic carbon content, organic carbon isotopic composition, and C / N ratio of modern soils from Chinese Loess Plateau, in order to obtain the relationship between soil magnetic susceptibility and other parameters, as well as how soil organic matters affect soil magnetic susceptibility. Materials and methods Fifty modern soil samples were collected from the Loess Platform, forest areas at the Huangling and Huanglong Mount, and loess-desert area near the Tengger Desert. These soil samples represent modern soil types in the Loess Plateau. Samples were collected 2 — 3 cm below the surface. The sampling sites are at least 40 km away from any industrialized centers that could generate artificial, air-borne magnetic material. In this way, we minimized the effect of human and livestock activity. We tested magnetic susceptibility（ χlf）, organic carbon isotopic composition（δ~（13）C）, and organic carbon and nitrogen contents of these samples. Results The magnetic susceptibility varied from 26.6×10~（-8） ？ kg~（-1） to 61.4×10~（-8） m~3 ？ kg~（-1） for soils from the loess platform, and from 68.6×10~（-8） m~3 ？ kg~（-1） to 107.5×10~（-8） m~3 ？ kg~（-1） for soils from forest areas. The value of soil from forest areas is apparently higher than that from the loess platform. The magnetic susceptibility of soil samples from loess-desert area varied from 8.5×10~（-8） m~3 ？ kg~（-1） to 44.4×10~（-8） m~3 ？ kg~（-1）. δ~（13）C values of soil samples from the loess platform varied from- 22‰ to- 24.4‰. δ~（13）C values of soil samples from loess-desert area