A vacuum sampler for subsampling freeze-dried laminated sediments with the application toin situ frozen varves of Mondsee,Austria

A method was developed for subsampling freeze-dried laminated sediments that employs a vacuum to draw off sediment from the sample in a precise way. The technique was tested on anin situ frozen sediment core of Mondsee containing varves 2 to 7 mm thick. Material was subsampled for¹³⁷Cs dating.     

A new method for the determination of absolute abundance of diatoms and other silt-sized sedimentary particles

The determination of absolute abundances of diatoms in paleolimnological and paleoceanographic studies is now becoming a routine step in diatom paleoecological investigations. Several distinct methods have been described for establishing absolute diatom abundance. Each of these methods has its own strengths and weaknesses. The most common weakness in diatom preparation methods is the use of aliquot subsampling from an assumed well-mixed diatom suspension. Described here is a simple, efficient and inexpensive method that utilizes settling of diatoms through a 10 cm water column, which yields an effectively random distribution, and uses no aliquot subsampling. Only a few milligrams of sample are needed, permitting microstratigraphic analysis of, for example, individual varves. The method is shown to be both reproducible and accurate for sediments ranging in diatom concentration from less than 10 million to more than one billion diatoms per gram. Multiple slides or SEM stubs can be simultaneously prepared. The method works well for the analysis of most silt-sized microfossils or other sedimentary particles.     

A simple and effective method for preserving the sediment–water interface of sediment cores during transport

We describe a method for preserving the upper sediments of fragile sediment cores during transport from field sites and assess potential effects on subsequent laboratory analyses. This method addresses the need to minimize disturbance to the surfaces of unfrozen sediment cores used for paleoenvironmental or other high-resolution sedimentological analyses during transport. A polymer gel (sodium polyacrylate) applied above the sediment surface acts as a barrier to movement while also preserving surface undulations. The gel seal can preserve even exceptionally fine sedimentary structures (<0.2 mm) in the upper sediments of lacustrine and fiord sediment cores, but may react with organic material (e.g. algal mats) present on some sediment surfaces. This reaction creates an adhesive layer at the gel’s base but it can be handled effectively during sampling. The gel seal minimizes surface deformation and preserves surficial sediments better than traditional seals made of water-absorbent floral foam, wax or paper towel. In addition to permitting detailed sedimentary and subfossil investigations of the sediment–water interface, this method shows no detectable effects on measurements of total organic carbon or total nitrogen values in the sediment. This method is inexpensive, non-hazardous and applicable to many coring systems and sediment types.     

A sledge microtome for high resolution subsampling of freeze cores

We describe a sledge microtome designed for the high-resolution subsampling of freeze cores. This inexpensive freeze-core microtome is capable of producing precise subsamples at mm to sub-mm resolution without sediment loss and cross-contamination. Such a subsampling resolution permits recognition of sub-decadal to annual events even in systems with low sedimentation rates. The freeze-core microtome is particularly useful for obtaining high-resolution subsamples at the environmentally important sediment-water interface due to freeze corers being capable of capturing this boundary with minimal disturbance as compared to other coring methods.     

Freezing characteristics of a highway subgrade

Temperature and moisture variations were experimentally investigated for the subgrade of the Astana-Burabai Highway, located in the northern region of Kazakhstan.Temperature and moisture were measured by means of specially manufactured sensors,including an element for temperature measurement based on the effect of thermal resistance and an element for moisture measurement through diamagnetic permeability.It was determined that the long-term average depth of frost penetration was 237 cm.In the upper part of the subgrade with 1 m of thickness,the average duration of a frozen condition decreases toward the bottom from 131 days to 117 days,with an average rate of 0.133 day/cm.The unfrozen water content decreases with the negative temperature reduction.In the case of high values of initial moisture (12%~22%),the unfrozen water content does not depend on the initial moisture;and it decreases under the power law,with reduction of negative temperature.In the case of the lowest values of moisture (9%~12%),the unfrozen water content depends also on negative temperature;but its values are considerably lower.     

Internal Structure and Permafrost Characteristics of the Rock Glaciers of Southern Carpathians (Romania) Assessed by Geoelectrical Soundings and Thermal Monitoring

Six rock glaciers in the Southern Carpathians have been investigated by means of geoelectrical soundings in order to detect their internal stratigraphy and the existence of frozen sediments. In the case of three relict rock glaciers, the electrical resistivity measurements indicated a typical internal structure. Low resistivity values (<10 kΩm) which are typical of unfrozen fine‐grained materials were obtained, but high resistivity values (25–240 kΩm) measured in the Pietroasa, Ie?u and Pietrele rock glaciers denote the presence of sediments cemented by interstitial ice and ice lenses. Based on the moderate resistivity values, the ice content is probably low to medium in the upper portion of these rock glaciers, that is, above 2040 m. At two sites (Pietroasa and V?iuga rock glaciers), ground surface temperature (GST) evolution was monitored using digital dataloggers. Mean annual ground surface temperature and GST regime throughout the winter were extracted from the recordings and confirmed the probability of permafrost occurrence in Pietroasa rock glacier. In the Ie?u and Pietrele rock glaciers, measurements of bottom temperatures of the winter snow cover were performed in March 2012. Considering the thick active layer, the reduced ice content and the presence of scarce vegetation on their surface it could be assumed that the permafrost exists in marginal conditions in the Southern Carpathians. The ground ice in permafrost is produced by the groundwater freezing or by snow banks buried by coarse angular boulders following large rockfalls.     

A portable extruder for accurate and precise high-resolution subsampling of unconsolidated sediment cores

Journal of Paleolimnology - We developed a portable extruder for precise and accurate high-resolution subsampling of unconsolidated sediment cores. This extruder is capable of producing subsamples...     

A field extruder for rapidly sectioning near-surface cores from lakes and wetlands

The soft uppermost sediments in lakes and wetlands contain important records of past environmental change. Although the technology for coring these sediments is relatively well established, there has been a continuing effort to improve the design of equipment that can provide the precise volumetric samples required for high-resolution dating and elemental analysis. Soft-sediment cores are usually sectioned near a coring site under a wide range of field conditions creating a challenge for both field crews and equipment. A new field extruder was therefore designed to simplify the process of fine-sectioning these cores in the field while improving volumetric-sampling accuracy. The new extruder is relatively light, stable, and easy to use, but sufficiently strong to extrude long continuous cores of stiff sediment if required. The key features of this extruder minimize sampling errors by enabling an operator to automate the measurement and extrusion of a pre-determined volume of sediment. The extruder was successfully field tested on a variety of sediment types in a large wetland from southern Florida, USA and proved easy to master by even inexperienced field crews.     

Review of the influence of freeze-thaw cycles on the physical and mechanical properties of soil

Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its physical properties changes during the freeze-thaw process; repeated freeze-thaw cycles change the characteristics of soil, which can render the soil from an unstable state to a new dynamic equilibrium state. The freezing process changes the structure coupled between the soil particle arrangements, which will change the mechanical properties of the soil. The method of significance and interaction between different factors should be considered to measure the influence on the properties of soil under freeze-thaw cycles.     

塔里木沙漠南缘安迪尔河水文特征分析

安迪尔河位于塔里木沙漠南缘,发源于昆仑山,上游河水沿河床大量入渗,中游为干河床,下游为泉水溢出补给型河流。安迪尔河缺乏水文资料,以临时水文站1998年实测水文资料为依据,对安迪尔河的水文特征进行分析,以便说明泉水型河流水文特征。分析了安迪尔河水位年内变化、冰期水位、畅流期水位、洪水期水位的变化特征;对安迪尔河水位流量关系进行了分析,建立了相应的水位流量关系方程式,并对冰期、畅流期的、洪水期逐日平均流量和流量特征进行了推求和分析,安迪尔河1998年泉水溢出量为0.5528亿m3。     

Geocryological characteristics of the upper permafrost in a tundra-forest transition of the Indigirka River Valley,Russia

Understanding geocryological characteristics of frozen sediment, such as cryostratigraphy, ice content, and stable isotope ratio of ground ice, is essential to predicting consequences of projected permafrost thaw in response to global warming. These characteristics determine thermokarst extent and controls hydrological regime—and hence vegetation growth—especially in areas of high latitude; it also yields knowledge about the history of changes in the hydrological regime. To obtain these fundamental data, we sampled and analyzed unfrozen and frozen surficial sediments from 18 boreholes down to 1–2.3 m depth at five sites near Chokurdakh, Russia. Profiles of volumetric ice content in upper permafrost excluding wedge ice volume showed large variation, ranging from 40 to 96%, with an average of 75%. This large amount of ground ice was in the form of ice lenses or veins forming well-developed cryostructures, mainly due to freezing of frost-susceptible sediment under water-saturated condition. Our analysis of geocryological characteristics in frozen ground including ice content, cryostratigraphy, soil mechanical characteristics, organic matter content and components, and water stable isotope ratio provided information to reconstruct terrestrial paleo-environments and to estimate the influence of recent maximum thaw depth, microtopography, and flooding upon permafrost development in permafrost regions of NE Russia.     

Direct shear tests of coarse-grained fillings from high-speed railway subgrade in cold regions

In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway, large scale direct shear tests were conducted with different normal pressures, water contents and temperatures. The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures, in both unfrozen and frozen states. This phenomenon was mainly due to the shear dilatation deformation effect. The shear displacement-shear stress curves show similar stages. Besides, the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state. In both the unfrozen or frozen states at the same water contents, the shear strength increased with increasing normal pressure.     

Moraine Formation at an Advancing Temperate Glacier: Brigsdalsbreen, Western Norway

Owing to increased winter balances especially since AD 1988/89, almost all valley outlet glaciers of Jostedalsbreen in western Norway are experiencing the largest advance since that of the early 18th century, the regional "Little Ice Age" maximum. Brigsdalsbreen advanced 441 m between 1987 and 1997. By the end of this period, the glacier had reached the outlet of the proglacial lake Brigsdalsvatnet, ploughing into unfrozen, fine-grained, water-soaked glaciolimnic sediments from the lake bottom and forming frontal moraines. These moraines are characterised by a lack of internal structures and preferred fabric. Owing to the strong advance, the moraine morphology is constantly changing, leaving only temporary moraine ridges.
Observations made along the glacier front suggest that the formation of these moraines can best be described as "bulldozed moraines", since the term push moraine, commonly associated with advancing glaciers, should be restricted to permafront environments. Different processes involved in moraine formation at frontal and lateral glacier margins result from variations in proglacial sediment properties, microrelief and glacier dynamics. Among these processes, large boulders left in the proglacial areas are pushed forward, forming pressure ridges on the distal side. Some of the largest boulders ( c . 80–120 m³) are overturned or rotated by the glacier.     

非均匀风沙起动规律研究

文章将非均匀沙水流起动研究方法中采用的暴露度的概念引入到天然风沙起动的研究中, 对暴露度的统计规律进行了分析。利用风沙颗粒起动时力矩平衡的条件, 建立了天然风沙起动公式, 用风洞试验资料进行了验证。计算结果表明, 在非均匀沙起动粒径与平均粒径相当的条件下, 混合沙的起动风速较小的结论, 与实际情况相符。说明在天然风沙起动研究中采用暴露度来反映风沙不均匀性对起动的影响是合理的。     

An analysis of mechanisms of ice-wedge casting based on geotechnical centrifuge simulations

Here we interpret the outcomes of scaled geotechnical centrifuge simulation of ice-wedge casting in terms of the likely significance of Quaternary ice-wedge pseudomorphs observed within different host sediments. Six experiments were completed in which 1/30th scale models of an ice-wedge embedded within frozen host sediments beneath a 25 mm thick unfrozen active layer were thawed from the surface downwards in the geotechnical centrifuge under a 30 times gravity (30×g) acceleration. Host sediment granulometry and/or ice contents were varied in each model, with host materials comprising medium sands, fine sandy silts and silty clays. The model ice-wedge was 50 mm at the top, 150 mm deep, and extended across the full width of the 450 mm wide test box. Centrifuge scaling laws indicate that under an acceleration of 30×g, stress distribution was equivalent to a 13.5 m long section of a 4.5 m high and 1.5 m wide full-scale prototype ice-wedge, covered in an active layer of thickness equivalent to 0.75 m. Thermal regimes, measured pore pressures during thaw, observed thaw consolidation and measured host sediment geotechnical properties are utilised in the interpretation of casting mechanisms. During a single uniform thaw event it is shown that arching of infilling sediment and the formation of a void is likely if negative pore pressures are developed in the host sediment. In fine silt and clays high ice contents are more likely than in sands, thaw consolidation is greater, positive pore pressures encourage complete filling of the ice-wedge void, and soft sediment deformation is likely to cause deformation of the cast and reduce its width and depth. Though natural casting mechanisms are likely to be more complex than those simulated here, modelling experiments highlight the need for care when inferring original ice-wedge geometry from observed shape and size of Quaternary ice-wedge casts.     

Variability in diatom and chrysophyte assemblages and inferred pH: paleolimnological studies of Big Moose Lake,New York,USA

We measured variability in the composition of diatom and chrysophyte assemblages, and the pH inferred from these assemblages, in sediment samples from Big Moose Lake, in the Adirondack Mountains of New York. Replicate samples were analyzed from (1) a single sediment core interval, (2) 12 different intervals from each of 3 separate cores, and (3) 10 widely spaced surface sediment samples (0–1 cm). The variability associated with sample preparation (subsampling, processing, and counting) was relatively small compared to between-core and within-lake variability. The relative abundances of the dominant diatom taxa varied to a greater extent than those of the chrysophyte scale assemblages. Standard deviations of pH inferences for multiple counts from the same sediment interval from diatom, chrysophyte, and diatom plus chrysophyte inference equations were 0.04 (n=8), 0.06 (n=32), and 0.06 (n=8) of a pH unit, respectively. Stratigraphic analysis of diatoms and chrysophytes from three widely spaced pelagic sediment cores provided a similar record of lake acidification trends, although with slight differences in temporal rates of change. Average standard deviations of pH inferences from diatom, chrysophyte and diatom plus chrysophyte inference equations for eight sediment intervals representing similar time periods but in different cores were 0.10, 0.20, and 0.09 pH unit, respectively. Our data support the assumption that a single sediment core can provide an accurate representation of historical change in a lake. The major sources of diatom variability in the surface sediments (i.e., top 1.0 cm) were (1) differences in diatom assemblage contributions from benthic and littoral sources, and (2) the rapid change in assemblage composition with sediment depth, which is characteristic of recently acidified lakes. Because scaled chrysophytes are exclusively planktonic, their spatial distribution in lake sediments is less variable than the diatom assemblages. Standard deviations of pH inferences for 10 widely spaced surface sediment samples from diatom, chrysophyte and diatom plus chrysophyte inference equations were 0.21, 0.09, and 0.16 of a pH unit, respectively.     

松嫩平原盐沼湿地冻融期水盐动态研究--吉林省长岭县十三泡地区湖滩地为例

以吉林省长岭县十三泡地区湖滩地为例 ,选取有代表性的月份进行定位观测、实验和对比分析 ,研究了冻融期盐沼湿地水盐运移的特殊规律性。研究表明 ,盐沼湿地冻结期 ,由于冻层的存在 ,土体内产生的温度梯度、水势梯度 ,是冬季水盐积累的驱动力。在冻结期 ,冻层水盐自底层向上迁移 ;融冻期 ,冻层自地表向下及自暖土层向上双向融化 ,在冻层形成上层滞水 ,在冻层之下水盐从下向冻层迁移冻结。冻融期间盐沼湿地水盐迁移的热力学机制是松嫩平原土壤盐化发生机制的重要组成部分。     

Resistivity studies over the Flinders conductivity anomaly, South Australia

Summary. Seven Schlumberger resistivity soundings with maximum current electrode spacings of 20 km have been conducted south of Lake Frome in South Australia. These experiments were done partly to test new electrical sounding equipment and partly to investigate a large conductivity anomaly previously delineated by other workers using magnetometer array and MT methods (the 'Flinders'anomaly). These previous studies left some doubt as to the depth to the conductive region responsible for the anomaly.
The electrical soundings did not detect a buried conductive zone, which constrains it to lie deeper than 5–7 km. However, the study did show the surface sediments of the region to be very conductive; resistivities of 2–9 μm were measured over thicknesses of 50–400 m, with sediment thickness inferred to be up to 2 km to the north of the studied area. This raises the question of whether current channelling in the surface sediments could have been responsible for the earlier results. Simple modelling and application of the criteria given by Jones suggest this may be so.
The equipment used for this study is a low power (200 W), computer controlled system which employs synchronous stacking and other signal processing to achieve signal to noise improvement ratios of up to 1000.     

Mechanisms discussion of frost heave and test verifications of moisture migration

Herein we review research on the structure of the frozen fringe and one of its key characteristics（unfrozen water content）,and compare its current measurement methods,including pulsed nuclear magnetic resonance（NMR）,time-domain reflectometry（TDR）,calorimetry,thermometry,the sublimation method,and CT imagery.A freeze-thaw cycle experiment with remolded soil was conducted inside to verify the mechanism of frost heave,measuring such variables as soil-water potential,temperature,water supplement,and the position of the freezing front.Conclusions from the analysis of the experiment data are：（1） The soil-water potential,the water supplement,and the position of the freezing front vary with temperature; and（2） the temperature gradient induces the soil-water potential,which in turn provides a stable driving force for moisture migration.     

黄河中游河口龙门区间水沙变化特征分析

黄河中游河口-龙门区间是我国乃至世界上水土流失最严重的地区,多年来大规模的水利水保工程建设使得该区产流产沙条件发生明显变化,因此,分析该区水沙变化特征及水沙变化原因具有重要意义。选取黄河中游河口-龙门区间下游龙门站1957—2005年水沙量水文观测资料代替区间资料,进行一致性检验后,运用小波分析、Mann-Kendall趋势检验、均差累积等统计方法对河口-龙门区间水沙变化特征进行分析,结果表明:该区水沙年内分配不均匀,年际变化大;该区水沙都呈显著的减少趋势,径流量和输沙量分别具有两个和4个明显的阶段性变化特征;水沙双累积曲线显示该区沙特性发生明显变化。在此基础上,通过分析该区水土保持面积与减水减沙量的相关关系表明,其具有良好的线性关系,进一步验证了水利水保措施是该区水沙减少的主要原因这一结论。