Variation of the Fe/Mn ratio of ferromanganese crusts from the Central North Pacific: implication for paleoclimate changes

Hydrogeneticferromanganesecrusts(Fe Mn crustshereafter),areinorganiccolloidprecipitatesfromseawater,whicharebelievedtohaverecorded theevolutionofelementalandisotopiccompositionsof seawaterovertime[1—7].Studiesontraceelements andisotopeshavebroughtmoreinsightsthanstudies onironandmanganesecontents.TheMn/Feratio hasbeenconsideredtoreflectwaterdepth,deep wa teroxygenation[8,9],andhasalsobeensuggestedasa reliablecriterionfordistinguishingdifferentgenetic typesofferromanganesedeposits[10].Apossi…     

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau since 1.8 Ma recorded by major elements in sediments of the South China Sea

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau has been investigated in the study of global change. Core sediment samples drilled in the South China Sea during ODP Leg184 are the best materials for studying long-term variability of the East Asian monsoon. R-mode factor analysis of major elements in the fine grain-sized carbonate-free sediments (<4 μm) of the upper 185 mcd splice of ODP Site 1146 drilled during Leg184 in the South China Sea shows that Ti, TFe2O3, MgO, K2O, P, CaO, and Al2O3 are representative of a terrestrial factor. The variation in the terrestrial factor score is subject to chemical erosion in the source region and thus indicates the evolution of the East Asian summer monsoon. The terrestrial factor score has three stepwise decreases at ~1.3 Ma, ~0.9 Ma, and ~0.6 Ma, indicating the phased weakening of the East Asian summer monsoon is related to wholly stepwise, quick uplifts of the Tibetan Plateau since 1.8 Ma. The periodic fluctuation of the terrestrial factor score since ~0.6 Ma indicates that the glacial-interglacial cycles have been the main force driving the evolution of the East Asian monsoon. As in the case of Chinese loess, the long-term evolution of the East Asian monsoon recorded in sediments of the South China Sea reflects a coupled effect of the glacial-interglacial cycle and uplift of the Tibetan Plateau.     

Origin of illites in the Luochuan loess section

Morphology and composition of illite from the Luochuan loess section were investigated by TEM. The results show that most of the illite grains are characterized by rounded shapes and chemical compositions are closely similar to those of anchizonal illites. The enrichment of illites in paleosol over loess was mainly caused by the weak winter monsoon during the interglacial periods, and was not related to thein situ pedogenesis. Illite can serve as an indicator for tracing eolian dust from Loess Plateau in pelagic and lacustrine sediments.     

Summer monsoon and dust signals recorded in the Dasuopu firn core, central Himalayas

In September 1997, a 15-m firn core was recovered from an elevation of 7 000 m a. s.l. from the Dasuopu Glacier in the central Himalayas. The analysis of δ18O values and major ion (Ca2+ , Mg2+ , NH4+ , SO42- and NO3-) concentrations shows that average annual accumulation is 0.75 m (water equivalent) in the Dasuopu firn core. The seasonal variations of δ18O values and major ion concentrations in the core indicate that present summer monsoon and dust signals are recorded with high-resolution in the Dasuopu Glacier. δ18O in precipitation are controlled by amount effect in summer monsoon season, more negative δ18O is representative of summer monsoon signal in snow layers. Higher concentrations of Ca2+ , Mg2+ , SO42- and NO3-are dominated by spring dust storm imput derived from the arid and semi-arid desert regions in central Asia. Also EOF analysis verifies that high spring concentrations of major ions are consistent. Due to the possibly different sources, the secondary variations of NH4+ and NO3- are negatively relevant with that of Ca2+ and Mg2+ .     

Origin of illites in the Luochuan loess section——Evidence from TEM study

Morphology and composition of illite from the Luochuan loess section were investigated by TEM. The results show that most of the illite grains are characterized by rounded shapes and chemical compositions are closely similar to those of anchizonal illites. The enrichment of illites in paleosol over loess was mainly caused by the weak winter monsoon during the interglacial periods, and was not related to the in situ pedogenesis. Illite can serve as an indicator for tracing eolian dust from Loess Plateau in pelagic and lacustrine sediments.     

Modeling and simulation of dynamic carbonate deposition in a loess-paleosol sequence

A compartment model of dynamic deposition processes has been developed and tested in the Potou loess section of China. There are four components in the model : carbonate input of eolian dust, carbonate output of erosion, carbonate chemical equilibrium and soil water balance. A climate stochastic model software (CLIMAK) generates the daily weather data. The processes of eolian dust deposition, erosion, and pedogenesis simulate the complex process of carbonate deposition in a loess-paleosol sequence. We consider both climatic change and soil-forming factors. The results indicate that since the Late Pleistocene in Potou section, the mean carbonate fluxes from precipitation, eolian dust and erosion are 0.14g/cm~2/kg, 1.45g/cm~2/ka and 0.23g/cm~2/ka respectively. Of this, 91.2% of the carbonate input is from eolian dust.     

Sr-Nd isotope geochemistry of eolian dust of the arid-semiarid areas in China： Implications for loess provenance and monsoon evolution

Strontium (Sr) is a divalent alkaline earth element. Its ionic radius (0.113 nm) is slightly larger than that of calcium (0.099 nm), and Sr thus substitutes isomor- phously for Ca in many minerals. Neodymium (Nd) is a rare earth element. Its chemical prop…     

U-Pb ages of zircon grains reveal a proximal dust source of the Xiashu loess,Lower Yangtze River region,China

Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits （the Xiashu loess） in the lower reaches of the Yangtze River. Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau （CLP） have been proposed. Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique. This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess. The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior. Instead, the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River, indicating the dominance of proximal dust source. Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China, possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.     

High-resolution sedimentary record of hydrocarbon contaminants in a core from the major reaches of the Pearl River,China

The concentrations and compositions of hydrocarbon contaminants, and molecular marker indices in modern sediments from a core in the major reaches of the Pearl River were investigated. The sedimentary record of hydrocarbons in the core, in combination with²¹⁰Pb-dating, was used to reconstruct the pollution history of hydrocarbon pollutants in the Pearl River in the past 100 years.

     

Compound-specific carbon isotope compositions of individual long-chain n-alkanes in severe Asian dust episodes in the North China coast in 2002

Asian dust storms originating from the arid regions of central and eastern Asia and from the Loess Plateau in China frequently occur in spring [1,2]. Driven by the East Asian monsoon, Asian dust can be transported to northern Pacific Ocean[2―8]. Asian du…     

Molecular organic geochemical peculiarities of lacustrine core sediments in Fildes Peninsula,King George Island,Antarctica

The peculiarities of lipids in lacustrine core sediments from Fildes Peninsula, King George Island, Antarctica, are reported. The origin of high-molecular-weight n-alkanes, alkenes, fatty acids, alcohols Is supposed to be related to the abundant moss occurring in the sediments. Abundantiso- andanteiso-fatty acids that occur in the sediments indicate a relatively strong bacterial activity in non-ice-cover zone than in other regions in Antarctica. The C_18:2 unsaturated fatty acids mainly originate from autochthonous algae in the sediment pool, and the C_18:2C_18:0 ratios in the profile are controlled more by paleotemperatures than source assemblies. Long-chain alkenones were identified in freshwater lacustrine sediment in Antarctica for the first time, of whichPrymnesiophyceae is assumed to be the source organism. High relative abundance of C_37:4 homologue in long-chain alkenone well correlates to the severely cold climate in Antarctica.

     

洞庭盆地第四纪气候演变的沉积物地球化学记录

对洞庭盆地安乡凹陷东南部两护村ZKC1孔上新世末—第四纪沉积物的主量、微量和稀土元素以及粒度进行了分析,进而探讨洞庭盆地第四纪气候演变。曲线协变性及相关系数表明,ZKC1孔沉积物化学蚀变指数(CIA)与Cr、Ga、V、Nb、Be、Li、Sc、Th等微量元素含量呈明显的正相关。从陆相沉积物CIA及微量元素含量与温度和湿度正相关的概念出发,结合其他资料,重塑洞庭盆地第四纪气候演变过程:早更新世为冷干→暖湿→冷干→暖湿,中更新世为冷干→暖湿→冷干—温湿→暖湿,晚更新世为寒冷→温湿→寒冷,全新世总体为温湿—暖湿。这一结论与ZKC1孔孢粉组合特征反映的气候演变过程及中国东部第四纪气候演化基本吻合,说明沉积物CIA和微量元素含量较好地记录了第四纪气候演变信息。相关性分析表明洞庭盆地沉积物粒度对CIA无明显影响;CIA与沉积物粘土含量呈弱的正相关关系,应与湿热气候条件下有更强烈的风化和更多粘土矿物形成有关。     

Ice core dust particulate by XPS-SEM/EDAX

The ice core dust particulate sampled from Mt. Xixabangma has been analyzed by means of X-ray photoelectron spectrometer (XPS) and scanning electron microscope with energy dispersion X-ray analysis (SEM/EDAX). The results show that the contents of SO ₄ ²⁻ and SO ₄ ²⁻ in the surface layer of the dust are significantly higher than those in the subsurface layer (with the exception of organic sulfide). This difference indicates that the surface SO_x has been captured and then chemically converted by the atmospheric dust particulate before its deposition with snow, which is obviously different from those inner layer sulfates and sulfites contained by dust itself. In addition, it has been determined by SEM/EDAX that the dust contains relatively high concentrations of transition metal elements such as Fe and Ti oxides which could function as photocatalysts to the conversion of SO_x adhered on the surface of the dust, and consequently accelerate the deposition of SO_x to snow. Our research also demonstrates that the adsorptive carrying and the catalytic performance of the dust to the atmospheric SO_x are most important causes of the positive correlation between SO ₄ ²⁻ and dust concentration records in ice cores.     

High-resolution multi-proxy records of Asian monsoon activities from terrestrial sediments over the last 75,000 years

Our research group have investigated chronology and sedimentology of terrestrial sediments including loess-paleosols sediments over the last 75 ka at Lanzhou, northwestern China, and over the last 45ka at Tokyo, central Japan. Based on chronology of high resolution dating of ESR, TL, and IRSL and tephrochronology in these sediments, we investigated to reconstruct activities of Asian summer and winter paleomonsoons by using magnetic susceptibility, color reflectance and eolian dust concentrations over the last 75ka. Relations between standard curves of delta ~(18)O in GISP2 and color reflectance in loess-paleosol sediments of Linxia over last 140 ka shows that color reflectances are good proxy records indicating Asian summer paleomonsoon activity in time and are closely related to standard curve of delta ~(18)O in GRIP since the last interglacial. Also, relations between standard curve of delta ~(18)O in GISP2 and eolian dust concentrations over the last 75 ka at Lanzhou shows the Asian winter paleomonsoon activities have coincided with climatic changes in North Atlantic by GISP2 ice cores, and suggests that response of winter monsoon was rapid in global cooling stages, but slow in warming stage. Other results of our research in terrestrial sediments show as follows; 1) Horizons of Heinrich events from H1 to H4 in loess-paleosol sequences at Lanzhou. 2) Magnetic susceptibility and MS frequency dependent are possible to be available as proxy records for pedogenesis of tile Kanto Loam in Japan. 3) 8.2ka cooling event was recognized in Holocene loess-paleosol sequences at Lanzhou.     

Source apportionment for urban PM10 and PM2.5 in the Beijing area

Airborne particulate matter (PM2.5 and PM10) samples were collected at the Beijing Normal University sampling site in the urban area of Beijing, China in dry and wet seasons during 2001―2004. Concen-trations of 23 elements and 14 ions in particulate samples were determined by ICP-AES and IC, re-spectively. Source apportionment results derived from both Positive Matrix Factorization (PMF) and Chemical Mass Balance (CMB) models indicate that the major contributors of PM2.5 and PM10 in Beijing are: soil dust, fossil fuel combustion, vehicle exhausts, secondary particulate, biomass burning and some industrial sources. We have identified both regional common sources, such as vehicular emis-sions, particulate of secondary origin and biomass burning, as well as country-specific problems, such as sand storms and soil dust that should be addressed for effective air quality control.     

南黄海表层沉积物中生源要素的分布规律及其环境意义

【目的】研究南黄海表层沉积物中生源要素的分布规律及其影响因素。【方法】通过测定南黄海82个站位表层沉积物样品中生源要素的含量及表层沉积物的平均粒径,分析研究区表层沉积物中生源要素和沉积物粒径的分布特征,并从表层沉积物中有机质来源、沉积物粒度、水动力作用和环境等因素探讨其对生源要素分布的影响。【结果】南黄海表层沉积物中生源要素总有机碳(TOC)、总氮(TN)及总磷(TP)的含量与平均粒径存在显著的相关关系,近岸沉积物粒度较大,对应生源要素的含量较低,在南黄海中部海区的沉积物粒度较细,各生源要素的含量较高。【结论】表层沉积物的粒度是影响生源要素含量分布的主要因素,即粒度越细,表层沉积物中生源要素含量越高。同时,有机质来源和水动力作用在一定程度上也影响和控制着表层沉积物粒度及生源要素的分布。生源要素TP分别与TOC、TN之间相对较弱的相关关系和近岸河口等地生源要素的高值表明,可能存在其他外部环境因素也会对其含量造成影响。     

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

太湖现代沉积物的物质组成和形成条件分析

对太湖现代沉积物进行了X射线衍射分析、粒度分析和常量元素分析，由此推断它们的矿物成分、化学风化程度差异，并分析了不同的水动力条件和物源。太湖沉积物的主要矿物组成是石英、云母、正长石和钠长石，粘土矿物为伊利石、绿泥石、高岭石和蒙脱石。化学组成显示，太湖沉积物的烧失量较高，与上部陆壳平均化学成分相比，Na、Na、K、Mg亏损，Mn、Ti富集，上部陆壳成分标准化图表明其风化程度明显强于下蜀土。化学风化程度指标CIA、Na/K值和Fe/Mg值的变化也表明太湖沉积物的化学风化作用比下蜀土强，，并存在地域的差别。太湖沉积物的CaCO3含量明显较低，反映了太湖流域本身的特点。所有这些特征表明，太湖沉积物的形成不仅与物源、地域位置有关，而且明显受人类活动的影响。     

Speciation of the elements and compositions on the surfaces of dust storm particles： The evidence for the coupling of iron with sulfur in aerosol during the long-range transport

The speciation of the elements on the surface of the particles collected during dust storm and non-dust storm in Beijing and Inner Mongolia was studied by XPS. The major species of iron on the surface were oxides, sulfate, silicate,FeOOH and minor part sorbed on SiO2/Al2O3. Sulfate is the dominant species of sulfur on the surface. SiO2 and Al2O3 are the main components of Si and Al on the surface respectively.One of the most important findings was that the Fe(Ⅱ) (FeS and FeSO4) produced could account for up to 44.3% and 45.6% of the total Fe on the surface in the aerosol sample collected at that night and next day of the “peak” time of the dust storm occurring on March 20, 2002, while Fe2(SO4)3,one of the Fe(Ⅲ) species on the surface decreased from 67.1% to 49.5% and 48.0% respectively. Both S and Fe enriched on the surface of aerosol particles. Fe(Ⅱ) accounted for 1.3%-5.3% of total Fe in bulk aerosol samples during dust storm. These results provided strong evidence to support the hypothesis of the coupling between iron and sulfur in aerosols during the long-range transport, which would have important impact on the global biogeochemical cycle.     

Seven million-year iron geochemistry record from a thick eolian red clay-loess sequence in Chinese Loess Plateau and the implications for paleomonsoon evolution

Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe₂O₃ ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe₂O₃ ratio record from the red clay-loess sequence indicates that (ⅰ) variations of the free to total Fe₂O₃ ratios of the loess can correlate generally with the alternations of the loess and paleosol horizons; (ⅱ) the East Asia summer monsoon was stronger as a whole in Neogene than that in Quaternary; (ⅲ) the strongest East Asia summer monsoon may occur between 4.0 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.