山西耕作土壤样品磁性空间分异及其环境意义

本文分析了山西高原土壤耕作层(0-20cm)25个样品的磁性,用GIS空间分析方法,得出土壤磁化率平面分布等值线图和空间三维模型。磁化率空间分布机理如下:首先,强烈的人为影响使土壤中磁性矿物人为来源占有重要地位。第二,土壤磁性矿物以亚铁磁性的磁铁矿和磁赤铁矿为主导。第三,土壤磁化率极值差及其与母质之间的差异均受广泛而较均一的黄土母质的影响。第四,晋西北和晋中等区域出现土壤磁化率高值区域。第五,人为作用强烈影响掩盖了气温、降水等气候因子对土壤磁化率的作用。     

山西耕作土壤样品磁性空间分异及其环境意义

本文分析了山西高原土壤耕作层（0-20cm）25个样品的磁性,用GIS空间分析方法,得出土壤磁化率平面分布等值线图和空间三维模型.磁化率空间分布机理如下：首先,强烈的人为影响使土壤中磁性矿物人为来源占有重要地位.第二,土壤磁性矿物以亚铁磁性的磁铁矿和磁赤铁矿为主导.第三,土壤磁化率极值差及其与母质之间的差异均受广泛而较均一的黄土母质的影响.第四,晋西北和晋中等区域出现土壤磁化率高值区域.第五,人为作用强烈影响掩盖了气温、降水等气候因子对土壤磁化率的作用.     

六盘山朝那湫湖泊沉积物磁化率的环境指示意义

在古环境研究中,湖泊沉积物磁化率的环境指示意义通常被解释为:磁化率升高指示流域内侵蚀和径流搬运能力增强,间接反映降水较多,气候湿润;磁化率降低指示流域内侵蚀和径流搬运能力减弱,间接反映降水较少,气候干旱。本文结合多代用指标(粒度、TOC、C/N等)指示的环境变化信息,对六盘山朝那湫湖泊沉积物磁化率的环境指示意义进行综合判别。结果显示:朝那湫湖泊沉积物磁化率能够指示流域降水变化历史,且与邻近地区树轮等高分辨率气候记录有良好的对比关系,表明本文重建的结果可靠。同时,本文也揭示了湖泊沉积物磁化率不同以往研究的特殊环境指示意义:磁化率升高指示流域内侵蚀和径流搬运能力减弱,反映降水较多,气候湿润;磁化率降低指示流域内侵蚀和径流搬运能力增强,反映降水较少,气候干旱。这主要是由流域基岩成分、植被覆盖和雨型决定的。由于湖泊沉积环境和过程的复杂性,沉积物磁化率的环境指示意义具有多解性。因此,在不同的湖泊沉积研究中,应充分考虑影响磁化率的各种因素,并结合其他多种代用指标进行综合辨识,方可得出可靠结论。     

哈尔滨黄土炭屑记录的中晚更新世以来古火活动及其驱动机制

炭屑是探索古火活动和人类用火及其驱动机制的重要指标,为研究古环境和古气候的演变提供了一种新的途径。我国东北地区的炭屑研究较为薄弱,仅有的少数研究集中在全新世,缺少更长时间的沉积记录。为此,我们对哈尔滨黄土炭屑和总有机碳(TOC)进行分析,以重建中晚更新世以来松嫩平原东部的古火活动与古植被-古气候间的关系,并进一步探讨古火活动的驱动机制。结果表明,哈尔滨黄土炭屑形态揭示研究区主要以木本植物为主,炭屑粒度特征记录本地区为区域性古火事件。哈尔滨黄土-古土壤炭屑浓度曲线与TOC曲线比较吻合,古土壤炭屑浓度高,在弱古土壤层L1S1呈现出逐渐增加的趋势,表明温度的上升和生物量增多导致古火活动较为增强,揭示出古火活动主要受控于生物量。通过与Rb/Sr比值、全球CO_2S浓度以及深海氧同位素的对比,发现古火还受温度条件的限制。温度作为触发因素,对植物的生长和古火的发生起到了积极的作用,即温度影响木本植物生长,较高的温度导致更密集的蒸发,较低的温度会导致较高的有效湿度,从而对火灾的发生和植物的生长产生影响,这也指示了古火-植被-气候之间的复杂性。     

青藏高原东南部18ka以来气候与水文变化

青藏高原东南部众多封闭小湖的湖相沉积记录着重要的地理信息,是恢复当地晚更民以来古环境演变的理想材料。西藏海登湖和仁同分辨率的花粉组合,ＡＭＳ＾１４Ｃ测年及磁化率和有机质含量测定,揭示了研究区与鳊季风密切相关的古植被,古气候和古水文变化历史。高分辨率的花粉记录反映,在１６ｋａＢｍ,Ｐ,以前花粉组合以黎科（Ｃｈｅｎｏｐｏｄｉａｃｅａｅ）和蒿属（Ａｒｔｅｍｉｓｉａ）为主,花粉浓度很低,应为荒漠草原植被。     

胆结石的磁性研究

用磁天平对 33例胆结石样做了磁化率测试 ,结果表明 ,多数结石的磁化率为负 ,表现为抗磁性 ;少数结石的磁化率为正 ,表现为顺磁性。据磁化率值可以推测 ,磁化率绝对值大者 ,磁力治疗胆结石效果较好 ,磁化率绝对值小者 ,磁疗效果差 ,需要较强的磁场。     

黄土-古土壤原核生物群落对古气候变化的响应

【目的】黄土-古土壤序列是记录第四纪气候环境变化的良好载体,其内部的土壤微生物特征是蕴含土壤环境变化的重要信息。由于黄土与古土壤成壤环境的气候差异,微生物群落结构特征可能会有不同的响应,但针对该问题的研究还十分有限。【方法】选择任家坡(R)和九州台(J)两地黄土(RL和JL)-古土壤(RS和JS)序列,运用高通量测序技术和线性判别分析效应大小(linear discriminant analysis effect size, LEfSe)识别土壤原核生物群落结构和类群差异,基于原核生物分类单元功能注释(functional annotation of prokaryotic taxa, FAPROTAX)数据库进行群落功能预测,以及利用Mantel test探讨影响土壤原核生物群落稳定的环境因子。【结果】土壤中碳氮营养物质与气候变化的代用指标磁化率、Rb/Sr变化趋势一致,含量整体表现为古土壤(RS和JS)高,对应的黄土(RL和JL)低,这一特征在任家坡古土壤(RS)中尤为显著;在同一气候时期,九州台较任家坡更为干冷,并且九州台古土壤沉积阶段也受到较强冬季风的影响,使其气候冷干与暖湿转变呈渐变型。原核生物群落结构中酸杆菌门(Acidobacteria)、泉古菌门(Crenarchaeota)、绿弯菌门(Chloroflexi)等具有嗜热嗜温性质的细菌和古菌在任家坡黄土-古土壤(RL和RS)中丰度较高,芽单胞菌门(Gemmatimonadetes)、放线菌门(Actinobacteria)、厚壁菌门(Firmicutes)、广古菌门(Euryarchaeota)、异常球菌-栖热菌门(Deinococcus-Thermus)等耐旱、适宜极端环境中生存的细菌和古菌在九州台黄土-古土壤中(JL和JS)丰度较高。同时,生命产能、氮、锰、铁、氯元素循环相关功能基因在任家坡古土壤(RS)中表达量最高,而碳、氢、硫元素循环相关功能基因在任家坡黄土(RL)中表达量最高。与任家坡相比,九州台原核生物群落具有物种多样性高、功能种类少的特点。Mantel test分析进一步表明,有机碳(soil organic carbon, SOC)、含水率(soil water content, SWC)、总氮(total nitrogen, TN)和硝态氮(nitrate nitrogen, NO₃^--N)是影响任家坡原核生物群落和功能稳定的关键环境因子,而TN、SOC、pH值和铵态氮(NH₄⁺-N)是影响九州台原核生物群落和功能稳定的关键环境因子。【结论】在暖湿期,微生物群落分化出更多的功能种类,具有更旺盛的生命活动;在冷干期,微生物群落通过提高物种多样性来完成主要的生命活动功能,通过协同共生维持群落生存和稳定来适应环境胁迫。研究成果对认识气候变化对土壤微生物多样性和功能的影响具有重要意义。     

长期施肥对黄土旱塬农田土壤微生物丰度的影响

以长武黄土高原农业生态试验站的长期定位试验为平台,通过荧光实时定量PCR (real-time PCR) 技术,研究不同施肥制度下的黄土旱塬农田土壤微生物群落丰度,揭示长期不同施肥制度对土壤微生物群落的影响规律.结果表明: 单施化肥处理细菌数量较CK裸地增加21％,古菌增加32％;化肥配施有机肥处理细菌数量增加37％,古菌数量增加36％.化肥配施有机肥处理显著增加了土壤细菌和古菌的丰度.30年长期施氮肥处理导致氨氧化细菌(AOB)的增幅达7.13倍,而氨氧化古菌(AOA)的增幅仅为0.2倍.AOB对施肥的响应程度较高,尤其是对氮肥具有较高的敏感性.与单施氮肥和氮肥混施有机肥处理相比,施磷肥处理显著增加了固氮酶铁蛋白和甲烷氧化菌含量,撂荒地的固氮酶铁蛋白、亚硝酸还原酶和甲烷氧化菌含量显著高于耕作土壤.结合土壤基本理化性质的相关性分析结果,pH、全氮和有机碳含量是影响土壤微生物群落丰度的重要因子.总之,长期施肥显著改变了黄土旱塬农田土壤各微生物丰度,不同施肥模式、耕作方式对微生物群落丰度具有显著影响.     

沙漠／黄土过渡带13 Ka BP以来季风演化的古植被记录

利用花粉分析结果并结合有机碳δ＾１３Ｃ及高精度＾１４Ｃ测年等资料,阐明沙漠／黄土过渡区１３ｋａ ＢＰ以来古植被记录的季风气候事件。古植被经历了荒漠草原－干草原－半荒漠－湿润草原－荒漠－疏林草原－荒漠草原－草原－荒漠草原９个阶段。冰后期的半荒漠－湿润草原－荒漠对应于其中冷干－凉湿－冷干的Ｙｏｕｎｇｅｒ Ｄｒｙａｓ事件,全新世气候适宜期以及４．５－３．５ｋａ ＢＰ的另一气候料适宜期等在研究区均有明显表     

胆结石的磁性研究

用磁天平对33例胆结石样做了磁化率测试,结果表明,多数结石的磁化率为负,表现为抗磁性;少数结石的磁化率为正,表现为顺磁性。据磁化率值可以推测,磁化率绝对值大,磁力治疗胆结石效果较好,磁化率绝对值小,磁疗效果差,需要较强的磁场。     

The magnetic properties of loess and paleosol samples from the Chinese Loess Plateau spanning the last 22 million years

Magnetic measurements (susceptibility, isothermal and anhysteretic remanence, and quotients derived from these) are presented for a suite of loess and paleosol samples from sites on the Chinese Loess Plateau. The three sites, Xifeng, Dongwan and Qinan (QA-I), together span most of the last 22 million years. The results provide the first multi-parameter magnetic measurements from pre-Pleistocene loess/paleosol sequences that began accumulation in the early Miocene. Mass specific measurements have been corrected for carbonate concentrations which peak in the loess layers and range up to 57%. All the magnetic properties recorded indicate variability on both orbital and supra-orbital timescales. The changing magnetic properties allow the record to be divided into a sequence of eight sample groups that broadly parallel the main supra-orbital changes in magnetic susceptibility. The pre-Pleistocene parts of the record include intervals (mainly late Miocene and Pliocene) during which loess as well as paleosol layers are characterized by high values for properties such as frequency dependent susceptibility (χ_fd), usually associated with strong weathering. Most of the Miocene record prior to 8.5 Ma, with the exception of a brief interval from ca. 14.4 to 15.9 Ma, shows reduced values for indicators of pedogenic ferrimagnetic concentrations in both the loess and paleosol layers, as well as a low amplitude of variability between loess and paleosol values. The palaeoenvironmental implications of this part of the sequence are unclear since they hinge on the type of model of pedogenic magnetic mineral formation adopted. High-field remanence measurements indicate that the coercivity of the antiferromagnetic minerals represented declined progressively throughout the whole period in both the loess and the paleosol samples, though there is no unambiguous evidence for long-term diagenetic alteration of the magnetic properties on timescales beyond the orbital ones that drive the loess/paleosol alternations. The present results suggest caution in applying existing climofunctions based on magnetic susceptibility to deposits spanning the whole of the last 22 Ma.     

东海陆缘(浙南段)晚第四纪硅藻的发现及古环境分析

东海陆缘(浙南段)温州沿海以往第四纪沉积已开展了一些研究,见有丰富的有孔虫、孢粉等生物化石,但未发现硅藻。本项研究在温州CH6井、台州CH5井岩心中发现了大量硅藻化石,本文以温州CH6井丰富的硅藻化石为依据,建立了晚第四纪硅藻组合序列,划分为12个硅藻带,并恢复其古环境演替,根据四个AMS ^14C年代数据,其时代属早、中全新世。     

An assessment of magnetic and geochemical indicators of weathering and pedogenesis at two contrasting sites on the Chinese Loess plateau

We present the results of high stratigraphic resolution measurements of magnetic and geochemical parameters sensitive to weathering and pedogenesis at two ～ 2500 ky loess–palaeosol sequences on the Chinese Loess Plateau. The two sites, Duanjiapo and Luochuan, are located on a strong modern climatic gradient and should have been subject to a significantly different degree of precipitation and temperature during the period of loess accumulation. Comparison of the magnetic and geochemical parameters indicates a complex and inconsistent relationship both within and between sites. In particular, a previously suggested coherency between the amplitude of variations in magnetic susceptibility and the Rb/Sr ratio is shown not to be the case over the entire length of the sequence. This finding indicates that quantitative climatic reconstructions for Chinese loess which are based on any single magnetic or geochemical parameter should be treated with caution. ‘Difference’ plots, obtained by calculating the difference between coeval magnetic or geochemical parameters between the two sites appear may offer a useful means of characterising latitudinal gradients in weathering and soil forming intensity, and indicate increases in the intensity of summer monsoon strength after about 1200 ka and 600 ka.     

Timing and Spatial Distribution of Loess in Xinjiang,NW China

Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change. However, in contrast to the widely investigated loess deposits in the Chinese Loess Plateau, the Central Asian loess–paleosol sequences are still insufficiently known and poorly understood. Through field investigation and review of the previous literature, the authors have investigated the distribution, thickness and age of the Xinjiang loess, and analyzed factors that control these parameters in the Xinjiang in northwest China, Central Asia. The loess sediments cover river terraces, low uplands, the margins of deserts and the slopes of the Tianshan Mountains and Kunlun Mountains and are also present in the Ili Basin. The thickness of the Xinjiang loess deposits varies from several meters to 670 m. The variation trend of the sand fraction (>63 μm) grain-size contour can indicate the local major wind directions, so we conclude that the NW and NE winds are the main wind directions in the North and South Xinjiang, and the westerly wind mainly transport dust into the Ili basin. We consider persistent drying, adequate regional wind energy and well-developed river terraces to be the main factors controlling the distribution, thickness and formation age of the Xinjiang loess. The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system. However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin.     

High-resolution multi-proxy climate records from Chinese loess: evidence for rapid climatic changes over the last 75 kyr

The loess/paleosol sequence in loess layer L1 (Malan Loess) is investigated in three regions of the Western Chinese Loess Plateau. Nine pedogenic layers are found in L1 and three proxy climate indices, magnetic susceptibility (MS), grain size (GS) and CaCO₃ content, are measured at intervals of 0.2 kyr in order to recover records of monsoon climate variations. Time series of MS, GS and CaCO₃ content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr. The records show a high degree of similarity to the warm interstadials recorded in ice cores from Greenland and the Antarctic, and with Heinrich events in the North Atlantic, during the last glacial cycle. Bond cycles are also recorded by the Chinese loess records. Overall, our results indicate that numerous rapid changes in climate occurred in China during the last glacial cycle, but that the range of climate variations was smaller than recorded in Greenland.     

Calcium Nodules as a Proxy for Quaternary Paleoclimate Change on China’s Loess Plateau

Different proxies have been used to investigate Quaternary paleoclimate change. Here, we used weathering of calcium nodules in paleosols on China’s Loess Plateau as a proxy for Quaternary paleoclimate changes to provide an alternative indicator of these changes. Paleosol and carbonate nodules were collected from Luochuan and Lantian counties in Shaanxi Province, China. We found that this approach allowed quantitative reconstruction of temperature, rainfall, soil mineral composition, and the effects of weathering and leaching. The changes in carbonate content in the loess and paleosol sequences were controlled by alternating dry and wet climatic conditions. Nodule formation conditions were directly affected by the leaching and migration of elements. The loess and paleosol sequences developed calcium nodules, and their formation was closely related to the rainfall and leaching characteristics of the paleoclimate. The paleoclimate and soil minerals affected the vegetation types and directly influenced changes in the soil. During formation of the calcium nodules, the surface vegetation evolved slowly, and the number of species and quantity of vegetation both decreased.     

Kovalevskiella (Ostracoda,Timiriaseviinae), genre à mode de vie benthique depuis l'Oligocène,son adaptation à la vie interstitielle

This paper reviews the distribution of the fossil and recent Kovalevskiella. The fossil species of this group lived in a benthic environment (fresh and oligomesohaline environments) in Europe from the Upper Oligocene to the beginning of the Quaternary. The recent Kovalevskiella species are exclusively groundwater dwellers. A lacustrine paleoenvironment in southwestern France from the Lower Miocene, where Kovalevskiella lived abundantly, is studied in detail. The study reveals the paleoecologic characteristics of the species in question. The morphology of this fossil species is compared with that of the Recent groundwater Kovalevskiella and the slow rate of the evolutionary change of the carapace shape and structure of the Kovalevskiella group is emphasized. Evolutionary-ecologic explanations for this slow process are provided.     

Les plus anciennes occupations humaines en Chine

With thick loess sequence (in the North), well-developed alluvial sequences and numerous karstic cavities, China offers excellent recordings for deciphering the Quaternary story. Some of these attest human activity right from 2 My. This article presents the earlier sites known so far in China, until the appearance of the Acheulian, around 0.8 My.