湿润亚热带地区土壤磁性矿物对气候的响应及其机制

How the precipitation and temperature work to affect the soil magnetic minerals is the foundation question of soil environmental magnetism. However, most of researches are focus on the relationship between soil magnetic properties and precipitation. Southern China is located in the humid subtropical area which has a large range of climatic conditions, various soil types, and the temperature and precipitation show out-of-phase change tendency geo-spatially in mountain area. So it is an ideal region for understand the role of climate conditions change to the soil magnetic minerals. In this project, large number of samples of the lateritic red soil, red soil, yellow-red soil, yellow soil, yellow-brown soil and mountain meadow soil will be systematically collected from the eastern part of China humid subtropics, which is set along the precipitation/ temperature gradient. Rock magnetic measurements will be carried out to characterize magnetic properties including types, concentration and domain size of magnetic minerals. Chroma and diffuse reflectance spectrum measurements will be served to quantify goethite and hematite combined with rock magnetic measurements. Geochemical index will be used to characterize weathering/pedogenic intensity of the soils. It is aim to understand 1) the magnetic variation along the soil horizons and geo-spatial; 2) the relationship of the weathering/pedogenic intensity and the climate conditions; 3) the respond of soil magnetic minerals to climate change in humid subtropics and its mechanism. This project therefore provides initial studies on soil environmental magnetism in humid subtropics. It is useful to further understand on the linkage between soil magnetic properties and climate, and provides reliable magnetism proxies for paleoclimate research.

降水与温度如何影响土壤磁性矿物是土壤环境磁学的基础问题。然而，目前的研究主要探讨土壤磁性与降水的关系。中国南方湿润亚热带地区气候条件范围大、山地地区温度与降水在空间上反向变化、土壤类型丰富，是研究这一问题的理想区域。本项目拟在中国湿润亚热带东部地区，选择赤红壤、红壤、黄红壤、黄壤、黄棕壤和山地草甸土6种类型土壤作为研究对象，大致沿降水量/温度梯度选择典型土壤剖面进行采样。以系统的岩石磁学参数测量为主要手段，分析土壤中磁性矿物种类、含量及磁畴大小等磁学特征；利用色度、漫反射光谱测量，结合岩石磁学，定量研究针铁矿和赤铁矿含量；分析磁性矿物特征在不同土壤层次间和地理空间上的变化规律；以地球化学指标衡量不同类型土壤的风化/成壤强度，以之为桥梁，系统探讨湿润亚热带地区土壤磁性矿物对气候的响应及其机制。本研究有助于深入理解土壤磁性与气候的关系，可以为古气候变化研究提供可靠的代用指标。

中国南方湿润亚热带地区气候条件范围大、山地地区温度与降水在空间上反向变化、土壤类型丰富，是研究土壤磁性矿物对不同水热组合响应的理想区域。本项目在浙江省、福建省和广东省获得98个不同类型土壤剖面共计2615个土壤和母岩样品。通过系统岩石磁学测量，分析土壤磁性矿物种类、含量和颗粒大小等特征；通过色度和漫反射光谱测量，分析赤铁矿和针铁矿含量；通过常量地化元素和粒度测量，分析土壤风化成土强度。在此基础上，基本明确了磁性矿物在成壤过程中的生成-转化途径；阐明了气候条件（大气温度和降水）对磁性矿物生成-转化的影响；明确提出反映亚铁磁性矿物特征的常温磁学参数不能作为气候变化的代用指标；初步建立了基于次生赤铁矿和针铁矿光谱学特征的气候代用指标；发现土壤中存在不同热稳定类型的磁赤铁矿，认为其居里点具有潜在的气温指示意义。本研究有助于深入理解土壤磁性与气候的内在联系，可以为古气候变化研究提供可靠的代用指标。