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491.
Gordon R.M. Bromley Brenda L. Hall Kurt M. Rademaker Claire E. Todd Adina E. Racovteanu 《第四纪科学杂志》2011,26(3):305-317
Deposits preserved on peaks in the southern Peruvian Andes are evidence for past glacial fluctuations and, therefore, serve as a record of both the timing and magnitude of past climate change. Moraines corresponding to the last major expansion of ice on Nevado Coropuna date to 20‐25 ka, during the last glacial maximum. We reconstructed the snowline at Coropuna for this period using a combined geomorphic‐numeric approach to provide a first‐order estimate of the magnitude of late‐Pleistocene climate change. Our reconstructions show that snowline was approximately 550‐770 m lower during the last glacial maximum than during the late Holocene maximum, which ended in the 19th century, and ~750 m lower than today. While these values are similar to data from nearby Nevado Solimana, reconstructions from the neighbouring peak of Nevado Firura reveal a smaller snowline depression, suggesting the glacial response to climate forcing in the tropics is strongly influenced by non‐climatic factors. These data constitute some of the first directly dated palaeo‐snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical Andes was similar to late‐Pleistocene events at higher latitudes. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
492.
Gordon R.M. Bromley Joerg M. Schaefer Gisela Winckler Brenda L. Hall Claire E. Todd Kurt M. Rademaker 《Quaternary Science Reviews》2009,28(23-24):2514-2526
Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions.Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase. 相似文献
493.
Deciphering factors controlling trace element distribution in the soils of Karaduvar industrial-agricultural area (Mersin,SE Turkey) 总被引:1,自引:0,他引:1
Cüneyt Güler Musa Alpaslan Mehmet Ali Kurt Abidin Temel 《Environmental Earth Sciences》2010,60(1):203-218
In this study, 30 topsoil samples were collected from Karaduvar area (Mersin, SE Turkey) where at present various industrial
and agricultural activities are occurring. Using a five-step ultrasound-assisted sequential extraction (UASE) procedure, trace
elements in soil samples were partitioned into the following: (1) soluble-exchangeable; (2) bound to carbonates; (3) bound
to Fe- and Mn-oxides; (4) bound to organic matter and sulfide compounds, and (5) residual fraction. Concentrations of 11 trace
elements in the extracts were determined using ICP-MS. Total concentrations ranged between (in mg kg−1) 3.35 and 7.26 for As; 1.18 and 3.96 for Cd; 10.76 and 20.26 for Co; 37.99 and 63.48 for Cr; 18.55 and 243.1 for Cu; 338.7
and 565.6 for Mn; 4.42 and 6.44 for Mo; 148 and 279.3 for Ni; 10.12 and 73.71 for Pb; 17.93 and 36.55 for V, and 25.46 and
331.7 for Zn. Factor analysis was applied to dataset in order to discriminate between natural and anthropogenic pollution
sources and factors controlling the spatial distribution of trace elements in the area. Results suggest that distributions
of Co, Cr, Mn, and Ni are mainly controlled by lithological factors, whereas, distributions of Cu, Pb, and Zn can be attributed
to agricultural activities such as pesticide/herbicide use and fertilizer application, as well as irrigation with petroleum
hydrocarbon-contaminated groundwater. Highest concentrations of Cd and Mo are generally observed around the diesel-fired thermal
power plant and ATAŞ refinery. Highest concentrations of As and V are generally observed at the NW sector of the area; however,
no definitive source can be designated for both of these elements. 相似文献
494.
495.
496.
Holocene glacial rebound and sea-level change in NW Europe 总被引:1,自引:0,他引:1
497.
498.
Kurt A. Haberyan 《Journal of Paleolimnology》2001,26(2):219-223
Materials for constructing a simple piston corer are available at most well-stocked hardware stores, primarily using galvanized fence post for the barrel, and pipe for the drive rod and head. These are assembled with a modicum of machinist skills. In the field, this VolksCorer operates like similar corers; it is limited to relatively shallow water (about 10–15 m) and is poorly suited for down-the-hole coring, but it requires few specialized tools. Likewise, materials to construct the VolksExtruder are widely available; this extruder, although simple, allows very precise extrusion control. The very low cost of the corer and extruder (less than US$50 each) make them suitable for investigators operating with low budgets without sacrificing sample quality. 相似文献
499.
Material versus isobaric internal boundaries in the Earth and their influence on postglacial rebound
Most previous earth models used to calculate viscoelastic relaxation after the removal of the Late Pleistocene ice loads implicitly assume that there is no exchange of mass across the mantle density discontinuities on periods of tens of thousands of years (the material boundary formulation). In the present study, simple incompressible models are used to determine the Earth's behaviour in the case where the density discontinuity remains at a constant pressure rather than deforming with the material (the isobaric boundary formulation). The calculation of the movement of the boundary is more rigorous than in earlier studies and uses the local incremental pressure calculated at the depth of the boundary and allows for the vertical deformation caused by the change in volume as material changes phase. It is shown that the buoyancy modes associated with the density discontinuities decrease in strength and increase in relaxation time analogous to what results when the density contrast is reduced. Also, two viscoelastic modes arise from an isobaric boundary, which is also predicted when there is a contrast in rigidity or viscosity across a material boundary. The difference in predicted radial deformation between the isobaric boundary model and the material boundary model is largest for long-wavelength loads for which the material incremental pressure at depth is largest. If the isobaric boundary model is appropriate for the treatment of the mineral phase changes in the mantle on glacial rebound timescales, then previous inferences of the deep-mantle to shallow-mantle viscosity ratio based on large-scale deformation (spherical harmonic degree < 10) of the Earth and including data from the early part of the glacio-isostatic uplift are too small. 相似文献
500.
Kurt Leinenweber Andrzej Grzechnik Mary Voorhees Alexandra Navrotsky Nan Yao Paul F. McMillan 《Physics and Chemistry of Minerals》1997,24(7):528-534
High pressure perovskites in the system CaTiO3?CaSiO3 in the composition range from 0 to 50% CaSiO3 have been re-examined using powder x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. In runs performed at 9 GPa and 1200 °C, a solid solution is obtained with compositions ranging from CaTiO3 to near Ca(Ti0.65Si0.35)O3, and with the orthorhombic distortion in the CaTiO3 end-member diminishing to pseudocubic for Ca(Ti0.65Si0.35)O3. Raman spectra show intensity changes and band broadening which are attributed to the reduction of orthorhombic character, but still indicate lower than cubic symmetry for the entire solid solution range. An ordered intermediate, Ca2TiSiO6, has been recovered from a run at 14 GPa at 1200 °C. The space group is Fm3m, with a=7.410(2)?Å, and the compound has the double perovskite structure. In this structure, Si-rich octahedral sites and Ti-rich octahedral sites alternate along the three principal axes. Transmission electron microscopy confirms the presence of the Fm3m ordered structure, and also documents the presence of lesser amounts of at least three other ordered perovskite structures which are not resolved in the x-ray data. These may account for extra features observed in the Raman spectrum which are inconsistent with mode assignments for the Fm3m phase. Non face-centered ordering schemes for these regions are suggested based on modeling of the HRTEM patterns. 相似文献