共查询到20条相似文献，搜索用时 31 毫秒
1.
Timothy G. Fisher 《Journal of Paleolimnology》2004,31(3):377-382
A monopod and piston coring apparatus for coring water-saturated sediment is described. The lightweight apparatus can be used from either an ice platform or the ground surface and can be transported by aircraft. Using a piston, core recovery is increased to better than 90%, and depending upon the monopod height, 7 m-long cores can be obtained. Tips for coring in freezing temperatures are also given. 相似文献
2.
珠穆朗玛峰北坡东绒布冰川成冰作用的新认识 总被引：7，自引：3，他引：4
冰川成冰作用的研究对于选择冰芯钻取点具有重要的科学意义。前人对珠穆朗玛峰北坡冰川成冰作用的研究,由于缺少高海拔区域的实测资料而具有一定的局限性。文章通过1998年东绒布冰川垭口处(6 500 m a. s. l.)11 m冰芯和海拔6 450 m处20 m冰芯剖面的成冰作用过程研究,认识到由于水、热条件的逐年波动,冰川成冰作用也处于变化之中。珠穆朗玛峰北坡东绒布冰川高海拔区域,在一定的水、热条件下(如气温较低和降水量较大等),再冻结-重结晶作用依然占主导地位,该成冰作用至少在垭口部位是有分布的。而一般在气温较高或降水量较少等条件下,冰川的成冰作用则以冷渗浸-重结晶作用为主。 相似文献
3.
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. 相似文献
4.
Parachute-assisted gravity sediment corer (Algonquin Corer) 总被引：1，自引：0，他引：1
Details are outlined for the construction and use of an easily constructed and inexpensive parachute-assisted, gravity-driven, sediment coring device. This corer has been named the Algonquin corer since it was designed, tested and constructed at École Secondaire Algonquin, North Bay, Ontario. This corer utilizes an underwater parachute to effectively control and stabilize its descent, and a driving mechanism (hammer) to increase the penetration of the corer. Other innovative features are its corrective mercury and magnetic switches, which allow the user to precisely monitor both the position of the driving mechanism and the corer's angle of sediment penetration. These optional features may be constructed for use with this particular corer or constructed separately to enhance existing coring devices. Details of these features are provided and their functions outlined. The versatile features, cost-effectiveness and ease of construction of the Algonquin corer make it an effective and practical tool for conducting sediment analysis studies at all levels. It is also well suited for the instruction of coring techniques and paleolimnological methods at both the university and high school level. 相似文献
5.
An inexpensive improvement to lightweight percussion coring systems is presented. Non-stretching lines are often required to facilitate core sampling in hundreds of metres of water, unfortunately such lines are usually negatively buoyant, which creates difficulties in keeping lightweight core assemblies upright while lowering through the water column. The addition of urethane closed-cell foam to the core head creates buoyancy that vertically stabilizes the coring assembly within the water column and prevents the core barrel from contacting the sediment-water interface non-vertically. 相似文献
6.
Summary. The polarizations of shear waves recorded by networks of digital three-component seismometers immediately above small earthquakes near the North Anatolian Fault in Turkey display shear-wave splitting on almost all shear-wave seismograms recorded within the shear-wave window. This splitting is incompatible with source radiation-patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths. This paper interprets the phenomena in terms of widespread crack-induced anisotropy. Distributions of stress-induced cracks model many features of the observations, and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns. This evidence for widespread crack-induced anisotropy lends strong support to the hypothesis of extensive-dilatancy anisotropy (EDA) suggested by laboratory experiments in subcritical crack-growth. The crucial evidence confirming some form of EDA would be observations of temporal changes in shear-wave splitting as the stress field alters the crack density and crack geometry. There is some weak evidence for such temporal changes at one site, but further analysis of suitable digital three-component seismometer networks in seismic areas is required to confirm EDA. 相似文献
7.
Lucien von Gunten Christian Kamenik Marian Fujak Roberto Urrutia 《Journal of Paleolimnology》2012,47(4):583-600
Lake sediment records are underrepresented in comprehensive, quantitative, high-resolution (sub-decadal), multi-proxy climate
reconstructions for the past millennium. This is largely a consequence of the difficulty of calibrating biogeochemical lake
sediment proxies to meteorological time series (calibration-in-time). Thanks to recent methodological advances, it is now
possible. This paper outlines a step-by-step, specifically tailored methodology, with practical suggestions for calibrating
and validating biogeochemical proxies from lake sediments to meteorological data. This approach includes: (1) regional climate
data; (2) site selection; (3) coring and core selection; (4) core chronology; (5) data acquisition; and (6) data analysis
and statistical methods. We present three case studies that used non-varved lake sediments from remote areas in the Central
Chilean Andes, where little a priori information was available on the local climate and lakes, or their responses to climate
variability. These case studies illustrate the potential value and application of a calibration-in-time approach to non-varved
lake sediments for developing quantitative, high-resolution climate reconstructions. 相似文献
8.
Concern about coastal sedimentation in New Zealand is widespread. As a result, many regional councils now undertake monitoring programmes to understand the rate of change that is occurring within estuarine environments. A variety of techniques are used to understand estuarine infill from short‐term (fixed rods, marker layers, laser surveying) to long‐term studies (coring). Short‐term studies provide detailed but temporally restricted data sets, while coring studies provide long‐term generalised data. This paper reviews the common methods used within New Zealand and suggests that a combination of both methods is the ideal for understanding sediment infill. 相似文献
9.
We present a design for a piston corer that can take a sediment core up to 1 m long, with an undisturbed sediment–water interface.
The coring device possesses a tripod unit and a core-tube unit, the latter comprised of a core tube, a piston with a wire,
a drive weight in which the core tube is mounted and a steel rod. The tripod stands on the sediment surface during coring,
stabilizing the system and serving as an anchor point for the piston wire. A ball clamp, the critical component of the design,
is mounted on top of the tripod. The steel rod runs through the ball clamp and at its lower end, holds the drive weight and
the core tube. The ball clamp allows the core tube to slide downward, while the piston is held in a fixed vertical position
by the wire connected to the tripod. When the corer is lifted, however, the ball clamp locks. This makes it possible to operate
the corer with a single cable, because the piston is not subject to any lifting force when the corer is retrieved. The piston
remains in position in the core tube even if the collected sediment core is very short. The piston corer can be deployed from
a raft or a boat. 相似文献
10.
Bernd Wagner André F. Lotter Norbert Nowaczyk Jane M. Reed Antje Schwalb Roberto Sulpizio Verushka Valsecchi Martin Wessels Giovanni Zanchetta 《Journal of Paleolimnology》2009,41(3):407-430
Lake Ohrid is considered to be of Pliocene origin and is the oldest extant lake in Europe. A 1,075-cm-long sediment core was
recovered from the southeastern part of the lake, from a water depth of 105 m. The core was investigated using geophysical,
granulometric, biogeochemical, diatom, ostracod, and pollen analyses. Tephrochronology and AMS radiocarbon dating of plant
macrofossils reveals that the sediment sequence spans the past ca. 39,500 years and features a hiatus between ca. 14,600 and
9,400 cal. year BP. The Pleistocene sequence indicates relatively stable and cold conditions, with steppe vegetation in the
catchment, at least partial winter ice-cover of the lake, and oxygenated bottom waters at the coring site. The Holocene sequence
indicates that the catchment vegetation had changed to forest dominated by pine and summer-green oak. Several of the proxies
suggest the impact of abrupt climate oscillations such as the 8.2 or 4.0 ka event. The observed changes, however, cannot be
related clearly to a change in temperature or humidity. Human impact started about 5,000 cal. year BP and increased significantly
during the past 2,400 years. Water column mixing conditions, inflow from subaquatic springs, and human impact are the most
important parameters influencing internal lake processes, notably affecting the composition and characteristics of the sediments. 相似文献
11.
Although highly branched from the base, all shrubs have short main axes linking canopies to root systems. Main axes become increasingly segmented into independent canopy/stem/root segments as aridity increases across continents. The resulting hydraulic modularity has been proposed as an adaption to low soil moisture that prevents runaway embolism and minimizes risk of hydraulic failure. Here we test the hypotheses that (1) at a regional scale, the importance of axis-splitting species in communities declines with increasing elevation, as a proxy for precipitation, and (2) that this decline is explained by lower occurrence of low-elevation dominant species. We evaluated all species for axis splitting and determined importance values in plots along an elevational transect in the Mojave Desert. As predicted, as elevation increased, the total importance of axis-splitting species declined from 100% at low-elevation sites to 75% at the highest elevation site. However, this decline was not due solely to the decline of the lower elevation dominant species. At the high elevation site, the influx of new species resulted in a six-fold increase in species richness and almost all of the new high elevation woody eudicotyledonous species exhibited axis splitting; non-splitting species were represented by other growth forms. 相似文献
12.
Christof Pearce Holger Cremer Emmy Lammertsma Friederike Wagner-Cremer 《Journal of Paleolimnology》2013,49(1):31-43
Analysis of siliceous microfossils of a 79 cm long peat sediment core from Highlands Hammock State Park, Florida, revealed distinct changes in the local hydrology during the past 2,500 years. The coring site is a seasonally inundated forest where water availability is directly influenced by precipitation. Diatoms, chrysophyte statospores, sponge remains and phytoliths were counted in 25 samples throughout the core. Based on the relative abundance of diatom species, the record was subdivided into four diatom assemblage zones, which mainly reflect the hydrological state of the study site. An age-depth relationship based on radiocarbon measurements of eight samples reveals a basal age of the core of approximately 2,500 cal. yrs. BP. Two significant changes of diatom assemblage composition were found that could be linked to both, natural and anthropogenic influences. At 700 cal. yrs. BP, the diatom record documents a shift from tychoplanktonic Aulacoseira species to epiphytic Eunotia species, indicating a shortening of the hydroperiod, i.e. the time period during which a wetland is covered by water. This transition was interpreted as being triggered by natural climate change. In the middle of the twentieth century a second major turnover took place, at that time however, as a result of human impact on the park hydrology through the construction of dams and canals close to the study site. 相似文献
13.
J. Curt Stager 《Journal of Paleolimnology》1992,7(3):253-255
Instructions for construction and use of a simple and inexpensive sediment coring device are presented. The sampler is suitable for use in high school and undergraduate science courses. 相似文献
14.
Ian R. Patmore Carl D. Sayer Ben Goldsmith Thomas A. Davidson Ruth Rawcliffe Jorge Salgado 《Journal of Paleolimnology》2014,51(1):79-86
We present a design for a large diameter piston corer, deployed from a raft that is suitable for use in shallow lakes. The piston corer, known as Big Ben, consists of a core tube, a piston on a rope and a corer head, to which rods are attached to drive the tube into the sediment. A core catcher, which aids the support of the core tube when full of sediment, has been incorporated into the design. To extrude the sediment, a framework has been designed to keep the core tube upright and stationary and a modified bottle jack is used to push the piston upwards during the extrusion process. The practical operation of the Big Ben coring system from setting up a coring platform to collecting and safely extruding a core is detailed. Finally we summarise recent experiences of deploying the corer and highlight its potential uses in the developing field of multi-proxy palaeolimnology. 相似文献
15.
The diatom record of V95-2P, a 7.6 m long sediment core collected from 67 m depth, is the first from the east central portion of Lake Victoria. A soil horizon developed at the coring site shortly before 12,400 14C yr BP due to a lakewide desiccation event. The radiocarbon chronology of the older half of this core is problematic, but if our estimated chronology is correct, then aridity and evaporative concentration of the lake are indicated by the presence of Thalassiosira rudolfi from > 12,400 BP to about 10,000 BP. Abundant Aulacoseira and generally rising biogenic silica concentrations may reflect enhanced water column mixing and rising precipitation:evaporation ratios ca. 10,000-8400 BP. A lakewide reorganization of diatom assemblages occurred around 7200 BP, when Aulacoseira nyassensis largely replaced A. granulata and after which rainfall and wind-driven mixing became more seasonally restricted. Pronounced reductions in offshore diatom deposition, from about 8300-5800 BP and after 3500 BP, may have been related to declines in the duration and/or intensity of wind-driven mixing. Increased aridity, and possibly deforestation in the lake basin, is indicated after 1400 BP. 相似文献
16.
Summary. We present a table of rotational and elliptical splitting parameters for earth model 1066A, including all terms through second order in rotation and first order in ellipticity. An algorithm for calculating the second-order Coriolis splitting by summing over all modes which are coupled to first order is given in detail. Coupling to secular (or zero frequency) modes, as well as the usual seismic modes, can provide significant contributions to these splitting parameters. 相似文献
17.
Gravity corers have been in use for a long time and in many different configurations. There are, however, reasons for improvements
since new manufacturing materials have become available, and demands for accurate coring and sub-sampling in both research
and environmental monitoring have increased. The HTH-coring equipment, which has been tested for >10 years by several users,
is a further development of the Kajak-corer concept and has some unique features which are described here. To avoid contamination
in pollution studies, the equipment is made of stainless steel and plastic (polyoxymethylene and polyethylene), and the use
of these materials also makes the equipment more durable. The extruding device is the main improvement over previous versions.
It consists of a piston that seals perfectly to the core tube wall, a threaded rod that can be mounted on a foot plate, and
an extruder head with a stationary upper-half and a rotatable lower-half that is screwed along the rod. One 360°-turn gives
a 5-mm thick sediment increment that is scraped off using the sectioning tray. Sub-sampling is quick and accurate and can
be performed by one person. The equipment is constructed to allow coring and sub-sampling both in summer and winter. 相似文献
18.
Complex upper-mantle deformation beneath the North China Craton: implications for lithospheric thinning 总被引：3，自引：0，他引：3
The mechanism of lithospheric thinning of the North China Craton (NCC) remains controversial. To constrain the mechanism, this study investigated the upper-mantle deformation pattern of the craton by measuring shear wave splitting at the cratonic edge. The results, derived from data recorded at 47 stations, reveal a complex pattern of mantle deformation. Inside the eastern craton, the majority of fast direction trends SE–NW parallel to the tectonic extension direction accompanying with the lithospheric thinning. At the cratonic edge, 15 stations with only null splitting results indicate undetectable anisotropy beneath the stations. This may be due to upwelling or chaotic ascension of mantle flow. To the north, off the craton, large delay times and variation of splitting parameter with backazimuth are generated by the combination of lithospheric and asthenospheric anisotropy. Based on comparison of the splitting results and the predicted ones by the compelling models, it is likely that lithospheric delamination dominated the lithospheric thinning at the north edge of the NCC during the Mesozoic to Cenozoic. 相似文献
19.
A freeze corer was developed specifically for the sampling of unconsolidated surface sediments by in-situ freezing. The new device which is presented here is designed to be used to a water depth of up to 1000 meters and was successfully tested at a depth of 200 m. The corer consists of a high pressure resistant housing with a vacuum insulated jacket for the ethanol which can be chilled by separate cooling agents, adjustable stabilizing legs, an electrical pump and a freezing wedge of 100 cm length. The freeze coring can be performed from a platform or a boat by using only a single cable to pull it up or to lower it. All other equipment is inside of the resistant housing. The core sample can easily be cut into two distinct slabs by use of the freeze-protectors on the small sides of the freeze wedge. 相似文献
20.
Paleohydrologists sometimes use macrofossils of aquatic vascular plants as one of several independent lines of evidence to infer changes in past lake-levels. Typically, this usage relies on an assumption that the seeds of aquatic species are not dispersed far from the source plants. The water depth over the coring site at the time the seeds were deposited is inferred from the water depth at which the species generally grows today. We determined the water depths at which particular plant-remain types are deposited, and tested whether they can be used successfully as proxy evidence for lake level. The results should aid the interpretation of fossil seeds in paleohydrological studies. A total of 189 surface sediment samples from 13 lakes in Maine and Massachusetts were examined for plant remains, and vegetation was surveyed in the immediate vicinity of each sediment sampling-site. The seeds of some taxa were found in sediment from water-depth ranges much broader than those in which living plants occur. However, in combination, even plant-remain types with broad depth ranges can be used effectively to reconstruct water depth. Presence of plant-remain types can be used to infer water depth regardless of abundance. Test samples indicate that inferring water depth from plant remains works well for shallow, alkaline lakes in New England. 相似文献