Hematite and goethite are widely occurring chromogenic iron oxides in soils and sediments that are sensitive to climatic dry/wet shifts. However, only by accurately quantifying the content or ratio of hematite and goethite can they be applied reliably to palaeoclimate reconstruction. Compared to the Loess Plateau of China, hematite in the soils of southern China has not been sufficiently studied. We used diffuse reflectance spectroscopy (abbreviation DRS, including the first-derivative curves and the second-derivative curves of the Kubelka–Munk remission functions), combined with ignition at 950 °C, and X-ray fluorescence (XRF) to quantify the hematite content of four tropical-margin iron-rich soil profiles with different matrix compositions in the Leizhou Peninsula, China. We also examined the application of hematite quantification parameters in soils with different matrix compositions under the same climatic conditions. Our main findings are as follows: (i) DRS first-derivative curves can reflect the presence of goethite and hematite in soils, and their relative contents can be compared within the same profile. (ii) The second-derivative curve of the Kubelka–Munk remission functions can reflect the relative proportions of goethite and hematite and provide information about the degree of Al substitution. (iii) Combined with calibration equations, soil redness can reliably quantify the hematite content, but it is necessary to consider the effect of mucilage envelopes in the process of hematite formation. Additionally, we summarize various methods used for quantifying hematite, and the influence of soil matrix compositions, with the aim of providing a reference for hematite quantification elsewhere. We also propose a new indicator (ΔHmRed/HmRed) to help detect iron hydroxide/iron oxide changes in soils.

Aeolian activity on the Tibetan Plateau (TP) has profound effect on the Asian and global climate. In the southern TP, loess deposition widely occurred associated with the massive glaciers and large rivers, recording the interplay history among the aeolian activity, atmosphere, and cryosphere. However, the initiation age of the loess and the factor controlling the loess formation are still controversial. Here, three drilling cores were retrieved from Linzhi area, in the eastern Yarlung Zangbo River Basin of the southern TP, which reached the bedrock and documented the loess development in the southern TP. Based on the optically stimulated luminescence, electron spin resonance, paleomagnetism dating and relative paleointensity correlation, the basal age of the drilling core was constrained at 584 ka revealing the onset of significant aeolian activity on the southern TP. Synthesize this study and previous work on the loess age across the TP, three stages were identified, namely 3600, 2800-2700, and 1200-600 ka, with the age trending younger from north to south. Extensive loess development on the TP occurred between 1200 and 600 ka, which was mainly ascribed to the global cooling during the mid-Pleistocene Transition. During this time, the ampler glaciers extent significantly expanded, westerly displaced southward and the wind intensity also intensified on the TP, which resulted in the enhancement of dust generation, arid and windy condition, leading to the loess preservation and development on the TP. Moreover, numerous evidences suggested that the glaciers on the TP may significantly developed since 800 ka, then enlarged at 500-600 ka, which may lead to the massive dust/loess input to the TP, Chinese Loess Plateau and north Pacific Ocean.

In recent years, there has been an increasing interest in the use of soil color as a climatic proxy. We investigated the variation of soil chromaticity parameters in subtropical and tropical coastal areas in China and their relationships with climatic factors (mean annual precipitation and temperature). Latitudinal zonal soil profiles in the coastal areas of Fujian and Guangdong were selected for study, and chromaticity analysis of soil samples was performed using the CIELAB color system. The principal results are as follows: (1) Soil color in the coastal areas of Fujian and Guangdong is mainly controlled by hematite and goethite. Redness (a*) varies significantly with depth within the soil profiles, and two types of profile can be defined: type I in which a* decreases with increasing depth within the profile, and type II in which a* increases with increasing depth within the profile. (2) Overall, a*, b* (yellowness) and the b*/a* ratio do not show a significant relationship with latitude. The a* of some of the Fujian profiles and the Guangdong soil profiles are significantly negatively correlated with the MAP, the b*/a* of some of the Fujian is highly positively correlated with MAP. A precipitation threshold may exist for both sets of profiles. There is a high correlation coefficient between b*/a* and MAT, and a temperature threshold of similar to 23 degrees C is evident. b*/a* is correlated with MAP and MAT, and it can potentially be used as a climate proxy.

土壤磁性矿物的形成、转化、运移和保存与气候条件密切相关，其对气候的响应形式、敏感程度及机制是土壤环境磁学的基础研究内容。本研究选取亚热带山地不同海拔高度的三个土壤剖面作为研究对象。这三个剖面位置临近，在母质、地形和植被类型上基本无差异，成土因素差别主要体现在因海拔差异而导致的气候条件不同。对三个剖面进行环境磁学、色度、常量元素等参数的测量，探究土壤磁学特征对气候的响应及其敏感程度。结果表明：1、随着土壤发育，土壤中超顺磁（SP）、单畴（SD）细粒亚铁磁性矿物增加，次生反铁磁性矿物的含量也不断增加，亚铁磁性矿物增加的速率高于反铁磁性矿物。土壤磁性随着成壤强度的增加而增强。2、气候条件是三个研究剖面磁学特征随海拔规律性变化的主导因素。气候通过风化/成壤作用进而影响土壤中磁性矿物。3、降水量不是湿润亚热带山地土壤磁性增强的限制因子。气温通过化学反应速率和蒸发量调节土壤磁性矿物的生成、转化与保存，是山地垂直地带性土壤磁性差异的主导因素。亚热带山地土壤磁性矿物可以非常敏感地响应气温的微小变化。

选取闽粤沿海地区纬度地带性土壤剖面作为研究对象，利用CIELAB表色系统，对土壤样品进行详细的色度分析，重点探讨亚热带和热带沿海地区土壤色度参数变化规律及其与气候因子（年均降水和年均气温）间的关系。结果表明：（1）闽粤沿海地区土壤剖面颜色主要由赤铁矿控制，红度（a*）在剖面垂直方向上变化显著，存在a*升高型和a*降低型两种土壤剖面类型。（2）闽粤沿海土壤剖面色度参数a*、黄度（b*）和黄度与红度比（b*/a*）不具有纬向性规律变化。色度参数（a*、b*和b*/a*）与气候因子整体相关性较差。福建部分剖面（FJ1、FJ2序列）和广东土壤剖面的a*与年均降水呈现显著负相关，a*对降水响应程度高，两者可能存在一个降水阈值。广东部分剖面（GD1、GD2序列）中b*/a*与年均气温相关系数较高且具有一个约23℃的温度临界点。b*/a*与年均降水和年均气温均呈现出一定的相关关系，对气候响应敏感，可作为一个适用的气候代用指标。