Palaeoecological study on the Holocene valley development of the River Main, southern Germany

Tree-ring studies carried out on subfossil oak trunk deposits within the Holocene valley fills of the River Main can reconstruct phases of increased fluvial activities. These phases have been dated on the base of two absolutely tree-ring dated chronologies and in addition by ¹¹C-datings of eleven floating tree-ring scries of subfossil oaks.
Geological-pedological investigations reveal an alternation between increased and reduced fluvial activity during the Holocene.
Periods of increased gravel redeposition are dated by dendrochronology, and by ¹⁴C and cultural findings. Increased fluvial activity becomes more frequent towards Modern Times with culminations in the Middle Atlantic, the Subboreal, the Iron-Roman Age, the Main Middle Ages till earliest Modern Times, and in the last century.
On the sequence of Holocene river deposits there developed specific soil types as indicators for the age of the river deposits since the Last Glacial.
Among other palaeoecological results an important finding is the correlation between tree-ring width, flood-loam sedimentation, and soil development.     

The role of weathering and pedological processes for the development of sorted circles on Kvadehuksletta, Svalbard - a short report

The presence of silt-rich, fine-grained material at the center of the well-developed sorted circles on Kvadehuksletta, Svalbard, is a precondition for their development. Field work, laboratory work, and data from published studies indicate that the fine-grained material is a dissolution product of the dolomitic bedrock. The silt is accumulated in situ and by slope wash in terrain depressions. Chemical weathering and other pedogenetic processes, such as the translocation of silt, are of great importance in Arctic regions and can create the sedimentological prerequisites for cryogenetic processes, such as frost sorting and cryoturbation. Therefore, the bedrock composition and the composition of surficial material are considered to be important control factors for these processes.     

Lake sediments from Store Koldewey, Northeast Greenland, as archive of Late Pleistocene and Holocene climatic and environmental changes

A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25'N, 18°45'W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid-Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed.     

1990s长江流域降水趋势分析

依据国家气象局提供的实测月降水和日降水资料,运用Mann-Kendall(M-K)非参数检验法验证了降水趋势,并通过空间插补法,由点扩展到面,分析了1990s长江流域降水变化特征,发现1990s长江流域降水变化以降水在时间和空间分布上的集中度的增加为主要特点:时间上,年降水的增加趋势以冬季1月和夏季6月降水的集中增加为主;一日降水量大于等于50mm的暴雨日数和暴雨量在1990s也有了较明显的增加.空间上,年降水、夏季降水、冬季降水的增加都以中下游区的增加为主,尤其以鄱阳湖水系、洞庭湖水系的降水增加为主.1990s长江流域春季和秋季降水的减少以5月和9月两个汛期月份的降水减少为主,除金沙江水系和洞庭湖水系等少数地区外,流域大部分地区降水呈减少趋势.上述1990s出现的降水趋势明显与近年来全球变暖背景下长江流域各地区不同的温度及水循环变异有关.     

长江流域降水变化及其趋势演变

本文对中国长江流域降水趋势进行了分析.指出对月降水量而言,20世纪后50年不同区域出现1不胃的降水趋势变化特征.趋势插补法研究表明中国降水时空分布趋势十分明显.对长江流域长期降水资料分析研究指出夏季月份降水时间更集中,而对年降水而言在一些站则表现出明显的周期变化.     

Metastability of the 10- Phase in the System MgO-SiO2-H2O (MSH). What about Hydrous MSH Phases in Subduction Zones?

The so-called 10- phase of the MgO-SiO₂-H₂O (MSH) system wassynthesized with 100% yields from a 3: 4 MgO/SiO₂ gel at fluidpressure of 50 kb and 500 C, but only during runs of up to1 h and with total H₂O contents near 50 wt. % in the sealedcapsules. The water contents determined in the run productsindicate a chemical composition Mg₃Si₄O₁₀(OH)₂0.65 H₂O, whichis different from the composition reported by Bauer & Sclar(1981), which had 1 H2O molecule per talc formula. The 10-phase has a = 5.293(3) , b = 9.194(3) , c = 10.044(3) , ß=96.10(8)its calculated density is p_calc.= 2.672 g/cm³; the refractiveindices measured are n_x = 1.554. and n_x = 1.574. The compatibilityof mean refractive index, calculated density, and chemical compositionfalls within the category ‘excellent’ of Mandarino(1979). Runs of longer durations and with total H₂O again near 50 wt.%, seeded with the less hydrous phase talc with the same Mg/Siratio, show that the 10- phase breaks down in the range 30–70kb, 200–700 C to form more talc. Thus it is not the stablehydrous high-pressure equivalent of talc as reported by Yamamoto& Akimoto (1977), but a metastable phase, which cannot playany role as a natural mineral of the mantle or of subductionzones. If the tie-line forsterite-H₂O is stable in the MSH system,as it seems to be for the conditions of our experiments, mostof the hydrous, silica-poor, new high-pressure MSH phases maybe without significance for the Earth, except perhaps phaseA with as yet an ambiguous composition.     

Biotite Equilibria and Fluid Circulation in the Klokken Intrusion

Chemical variation in biotite from the KJokken gabbro-syeniteintrusion in the Proterozoic Gardar province in South Greenlandhas been investigated by electron probe and, for F and Li, ionmicroprobe. Most mica occurs in small amounts as fringes onilmenomagnetite or fayalite, rarely as an intercumulus or poikiliticphase. The micas range continuously from Phlog₇₀Ann₃₀ in a gabbro,to Phlog₄Ann₉₆ in the most evolved (slightly persilicic andperalkaline) syenite. In the syenites Fe-Mg partitioning betweenbiotite and olivine can be described by a single distributioncoefficient, K_d = XF X^Biot_Ms/X^Biot_Fe 3, suggesting that thesereactant phases mix ideally at the reaction T. Experimentaldata for Fe-Mg exchange via aqueous chloride solutions (Schulien,1980) imply low T (32Q?C). F was absent in the experiments andmay significantly affect the exchange equilibrium. K_d in thegabbros is 1, consistent with equilibrium via a fluid depletedin F because of crystallization of large amounts of amphibole. Al, Mn, and Ti vary regularly throughout the series and canbe used as markers of cryptic variation in the layered syenites.(Al + Si): 22 O is always in the range 7.7–7.85. A1/(A1+ Si) decreases from 0.31 in gabbros to 0.25 in the most Fe-richmicas. Li is always < 260 ppm w. In the syenite series, Fshows a near-linear inverse relationship with Fe/(Fe + Mg) whichpasses close to OF at Ann₁₀₀ with l.4 wt% F(0–7 F to 44positive charges) at Ann₄₄. Biotites in the gabbro unit (whichforms an outer sheath to the intrusion) have relatively lessF, probably because it was consumed by coexisting amphibole.^I8O is similar for both gabbros and syenites, and it is unlikelythat an envelope fluid was involved in the reactions. G reachesa maximum of 0.3 wt. % in biotite except for that in one syenitesample with 0–7 wt. %. Calculation of relative F-OH fugacitiesfrom the reaction OH-phlogopite + F-annite = F-phlogopite +OH-annite, as calibrated by Munoz (1984), appears to suggestthat each horizon in the layered series was in equilibrium witha slightly different fluid. In view of the intimate interleavingof these lithologies, this is improbable. The equilibrium constantof the exchange reaction, obtained from the experimental data,seems not to be appropriate to the Klokken assemblage, or toother examples of regular F-Fe avoidance. Explanations may includeshort-range Fe-Mg ordering in the natural examples or the effectof additional components in the fluid. F contents are high incomparison with biotites from calc-alkaline complexes; highmagmatic F may account for the igneous layering common in theGardar. Temperatures calculated from reactions involving fayaliteand magnetite show that most biotites grew subsolidus. The F-poorannites grew > 300 ?C subsolidus even when texturally intercumulus.Stable isotope data are consistent with the separation and retentionof a deuteric fluid during the final stage of magmatic crystallization.Klokken was not generally subject to the pervasive, long-range(in both distance and time) dydrothermal interactions demonstratedin calcalkaline and theleiitic intrusions, although more extensivefluid flow is indicated for the more permeable laminated syenites.The biotites preserve chemical variation indicating local equilibriumwith other mafic phases, and halogens provide a useful markerof subsolidus fluid flow.     

Regional Saharan dust modelling during the SAMUM 2006 campaign

The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006 SAMUM field campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry synoptic-scale dynamics, they are often misrepresented when dust emissions are caused by moist convection or influenced by small-scale topography that is not resolved by the model. In contrast to long-range dust transport, in the vicinity of source regions the model performance strongly depends on the correct prediction of the exact location of sources. Insufficiently resolved vertical grid spacing causes the absence of inversions in the model vertical profiles and likely explains the absence of the observed sharply defined dust layers.