Model of carbon fixation in microbial mats from 3,500 Myr ago to the present

Biological carbon fixation is an important part of global carbon cycling and ecology. Fixation that took place 3,500 million years ago is recorded in the laminated sedimentary rock structures known as stromatolites, which are fossilized remains of microbial mat communities. Stromatolites are the most abundant type of fossil found in the Proterozoic (2,500 to 590 Myr ago), but they then declined, possibly because of predation and competition. Using modern microbial mats as analogues for ancient stromatolites, we show that the rate of carbon fixation is higher at the greater levels of atmospheric CO2 that were probably present in the past. We suggest that carbon fixation in microbial mats was not carbon-limited during the early Precambrian, but became carbon-limited as the supply of inorganic carbon decreased. Carbon limitation led to a lower rate of carbon fixation, especially towards the end of the Precambrian. Thus, another reason for the decline of the stromatolites could have been a decrease in available CO2.     

Newly discovered Palaeolithic artefacts from loess deposits and their ages in Lantian,central China

Eight new Palaeolithic open-air sites were identified and 770 stone artefacts were collected from 2009 to 2011 in the Lantian area of the Bahe River valley, central China. Because the famous Homo erectus fossils were unearthed at the Gongwangling and Chenjiawo localities, and more than 30 Palaeolithic open-air sites were investigated in the 1960s in this region, the catchment of Bahe River is regarded as one of the most important hominin sites from the late early Pleistocene to the middle Pleistocene. These eight newly discovered open-air sites are located at the second(n = 6), third(n = 1) or higher terraces(n = 1) of the Bahe River. The Diaozhai section on the second terrace was sampled in detail. Two samples were collected for optically stimulated luminescence dating(OSL). The OSL results suggest that a buried lithic artefact layer at the Diaozhai site spans approximately 70–30 ka. The lithic assemblage analysis suggests that the stone artefacts were made of local pebbles/cobbles such as greywacke, quartz, sandstone and igneous rocks. The main percussion techniques that were used were direct hard hammer percussion and bi-polar techniques. The lithic artefacts comprise hammer stones, cores, flakes, retouched tools and flaking debris. Acheulian-type large cutting tools(LCTs) such as hand-axes, picks and cleavers were indentified in the Lantian region as well. This is the first time Acheulian-type LCTs from the late Pleistocene have been identified in this region. This study distinguishes age gaps between Western world and East Asian Acheulian-type tools.     

Ancestral echinoderms from the Chengjiang deposits of China

Deuterostomes are a remarkably diverse super-phylum, including not only the chordates (to which we belong) but groups as disparate as the echinoderms and the hemichordates. The phylogeny of deuterostomes is now achieving some degree of stability, especially on account of new molecular data, but this leaves as conjectural the appearance of extinct intermediate forms that would throw light on the sequence of evolutionary events leading to the extant groups. Such data can be supplied from the fossil record, notably those deposits with exceptional soft-part preservation. Excavations near Kunming in southwestern China have revealed a variety of remarkable early deuterostomes, including the vetulicolians and yunnanozoans. Here we describe a new group, the vetulocystids. They appear to have similarities not only to the vetulicolians but also to the homalozoans, a bizarre group of primitive echinoderms whose phylogenetic position has been highly controversial.     

The record of cultivated rice from archaeobiological evidence in northwestern China 5000 years ago

Pollen, plant seeds and phytoliths from an AMS dated sediment profile at the Xishanping site indicate that the cultivation of rice might start no later than 5070 cal. a BP in the region of Tianshui, Gansu Province. It continued from 5070 to 4300 cal. a BP. This is so far the oldest and the most northwestern record of cultivated rice in Neolithic China, which extends the known region of prehistoric rice cultivation at least 2° longitude to the west. This finding provides important evidence for reconstructing the cultivation region of rice at 5000 a BP （an important time period）, and its spreading history in East Asia, during the Neolithic.     

中国荒漠化地区沙产业发展风险的定量评价

从自然环境、市场环境和企业内部分析了中国荒漠化地区沙产业发展所面临的风险,提炼出9个风险评价二级指标,建立了沙产业发展的风险评价指标体系,给出了基于模糊评价法的风险定量评价模型.应用算例分析说明如何运用该模型对荒漠化地区沙产业发展所面临的风险程度进行定量评价.     

我国西南岩溶地区石漠化问题研究--以滇黔桂三省区为例

以云南、贵州和广西3省区为对象分析了我国西南岩溶地区石漠化的现状,研究了西南岩溶地区石漠化的机理.结果表明,广泛分布的碳酸盐岩是形成石漠化的地质背景;崎岖的地表为石漠化提供了动力;成土缓慢且土层薄使其允许侵蚀量小;受气候因素的影响岩溶地貌发育使土壤易“丢失”;人口的增长及不合理的行为导致植被破坏后恢复困难,易造成水土流失.在此基础上提出了石漠化的治理措施.     

从广州亚运会透视中国田径现状

本届亚运会中国田径女子项目集体出现下滑现象;男子则实现了个别项目的突破;亚洲整体田径出现集中现象,如何进一步缩小与高水平田径的国家的差距,保持优势项目的持久力以及扭转我国女子项目的下滑是我们面临的首要任务。     

Susceptibility variations of multiple origins of loess from the Ily Basin (NW China)

The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.     

A high-resolution climatic chanse since Holocene inferred from multi-proxy of lake sediment in westerly area of China

Multi-proxy data are presented and a discuss is made of paleoclimatic and paleoenvironmental changes during Holocene from a 225-cm-long sediment core from Wulungu Lake, located in westerly area of China. The chronology is constructed from six AMS radiocarbon dates on the bulk organic matter. Analyses of pollen, TOC, TN, δ^13Corg, ostracod assemblages and the shell stable isotopes, suggest Holocene climate pattern as follows： temperate and dry （10.0-7.6 cal. ka BP） -warm and wet （7.6-5.3 cal. ka BP） -warm and moist （5.3-3.6 cal. ka BP） -temperate and dry （3.6-2.1 cal. ka BP）-temperate and moist （2.1-1.3 cal. ka BP） -cool and dry （1.3 cal. ka BP-present）. With the climatic change, Wulungu Lake experienced two large-scale retreat （5.3-3.6 cal. ka BP and 1.3 cal. ka BP-present） and an obvious transgression （7.6-5.3 cal. ka BP）. The records of climatic and environmental evolution of Wulungu Lake were in good accordance with those of adjacent areas. It responded to regional environmental change, global abrupt climate events and followed the westerly climate change mode.     

A high-resolution climatic change since Holocene inferred from multi-proxy of lake sediment in westerly area of China

Multi-proxy data are presented and a discuss is made of paleoclimatic and paleoenvironmental changes during Holocene from a 225-cm-long sediment core from Wulungu Lake, located in westerly area of China. The chronology is constructed from six AMS radiocarbon dates on the bulk organic matter. Analyses of pollen, TOC, TN, δ 13Corg, ostracod assemblages and the shell stable isotopes, suggest Holocene climate pattern as follows: temperate and dry (10.0―7.6 cal. ka BP)-warm and wet (7.6―5.3 cal. ka BP) -warm and moist (5.3―3.6 cal. ka BP) -temperate and dry (3.6―2.1 cal. ka BP)-temperate and moist (2.1―1.3 cal. ka BP) -cool and dry (1.3 cal. ka BP―present). With the climatic change, Wulungu Lake experienced two large-scale retreat (5.3―3.6 cal. ka BP and 1.3 cal. ka BP―present) and an obvious transgression (7.6―5.3 cal. ka BP). The records of climatic and environmental evolution of Wulungu Lake were in good accordance with those of adjacent areas. It responded to regional environmental change, global abrupt climate events and followed the westerly climate change mode.     

荒漠化扩展对我国区域气候变化影响的数值模拟

使用区域气候模式RegCM3研究了西北沙漠面积变化对我国区域气候变化的影响．共设计了3组试验：控制试验A、沙漠面积扩展试验B、在试验B基础上增大粗糙高度的试验C．分析表明：中国西北沙漠区扩展后对中国夏季降雨量和中国夏季风有明显影响．结果表明：植被退化、荒漠化加剧会导致季风减弱,降水量减少,增大地面粗糙高度后的影响更为显著．     

The early Holocene optimum inferred from a hish-resolution pollen record of Husuansyan Maar Lake in southern China

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that （i） pollen percentage of trees and shrubs reached 56% during the early Holocene （11600-7800 cal a BP）, of which the pollen percentage of tropical trees reached a maximum at 9500-8000 cal a BP, reflecting a hot and wet environment; （ii） during the mid-Holocene （7800-4200 cal a BP）, the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; （iii） in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500-8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.     

中国南方岩溶地区脆弱的生态环境及石漠化过程

中国南方岩溶地区分布有面积广泛的碳酸盐岩,发育多种岩溶地貌。由于该地区的特殊地质、水文、气候等自然因子的影响,其岩溶生态环境非常脆弱,环境容量低,敏感度高,抗干扰能力弱。当人类对森林进行破坏使森林的“生物泵”作用消失后,引发出一系列的生态问题：岩溶生态环境开始恶化,植被走向逆向演替等。最后出现大面积的石山,发生石漠化现象。可见,森林在岩溶生态系统中的作用是十分重要的,是影响岩溶生态系统的关键因子。     

The early Holocene optimum inferred from a high-resolution pollen record of Huguangyan Maar Lake in southern China

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that (i) pollen percentage of trees and shrubs reached 56% during the early Holocene (11600―7800 cal a BP), of which the pollen percentage of tropical trees reached a maximum at 9500―8000 cal a BP, reflecting a hot and wet envi- ronment; (ii) during the mid-Holocene (7800―4200 cal a BP), the pollen percentage of montane conif- erous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indi- cating lower temperature and humidity; (iii) in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500―8000 cal a BP in south- ern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer mon- soon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.     

Evidence from episodic seamount volcanism for pulsing of the Iceland plume in the past 70 Myr

The North Atlantic volcanic province has been attributed to continental rifting about 60 Myr ago over an Iceland plume head with a diameter of 1,000-2,000 km (refs 1, 2). But evidence from a few igneous centres has been used to infer that earlier plume activity occurred in this region. The three seamounts in the Rockall trough off the Atlantic coast of Scotland are among the few accessible remnants of such early plume activity. Here we present 40Ar-39Ar incremental-heating ages of samples from these seamounts, which show that volcanism began there in the late Cretaceous period (70 +/- 1 Myr ago), and then continued for the next 30 Myr in at least four discrete phases: 62, 52, 47 and 42 Myr ago. We relate this activity to pulsing of large masses (approximately 10(8) km3) of hot Iceland plume material on timescales of 5-10 Myr. This significantly extends the time span for Iceland plume activity both backwards and forwards in time, and provides a possible alternative to the 'plume head' models for the formation of continental flood basalts.     

Comparisons of grain size characteristics of red earth from southern China with that of loess and dune sand from Bering region

The comparisons of grain size distributions among eolian deposits along the monsoon wind trajectory are a fundamental task for the reconstruction of the past wind regimes. Here the authors sampled the dune sands in Hunsandak desert, loess deposits in Beijing region and red earth in southern China. Grain size analyses show that the distribution models of the loess and dune sand samples are unimodal whereas the red earth and paleosol are polymodal. The red earth, paleosol, loess and dune samples are distinguished and closely related to one another in grain size parameter diagrams. Moreover, the grain size distributions and parameters of the red earth and paleosol are similar, implying that the red earth in southern China and the paleosol in northern China had the same origin.     

History of trace gases in presolar diamonds inferred from ion-implantation experiments

Diamond grains are the most abundant presolar grains found in primitive meteorites. They formed before the Solar System, and therefore provide a record of nuclear and chemical processes in stars and in the interstellar medium. Their origins are inferred from the unusual isotopic compositions of trace elements-mainly xenon-which suggest that they came from supernovae. But the exact nature of the sources has been enigmatic, as has the method by which noble gases were incorporated into the grains. One observation is that different isotopic components are released at different temperatures when the grains are heated, and it has been suggested that these components have different origins. Here we report results of a laboratory study that shows that ion implantation (previously suggested on other grounds) is a viable mechanism for trapping noble gases. Moreover, we find that ion implantation of a single isotopic composition can produce both low- and high-temperature release peaks from the same grains. We conclude that both isotopically normal and anomalous gases may have been implanted by multiple events separated in space and/or time, with thermal processing producing an apparent enrichment of the anomalous component in the high-temperature release peak. The previous assumption that the low- and high-temperature components were not correlated may therefore have led to an overestimate of the abundance of anomalous argon and krypton, while obscuring an enhancement of the light-in addition to the heavy-krypton isotopes.     

从团粒结构失稳角度探讨由灌溉引起的黄土湿陷发生机理

利用SEM/EDX等测试手段,探讨了由灌溉引起的黄土湿陷发生机理.结果表明:黄土湿陷过程包括初始快速变形和后续迟缓变形2个阶段,这2个阶段的发生都与黄土的骨架颗粒--团粒有关.前者是由于黄土中非水稳性团粒遇水破坏所至,而后者是因为水的渗透造成黄土团粒主要胶结物碳酸钙的淋溶移动损失,从而导致失稳.黄土中松散结构或架空孔隙的存在是产生湿陷的重要条件,但不是湿陷发生的根本原因.