Continuous record of environmental changes in Chukotka during the last 350 thousand years     

A. V. Lozhkin  P. M. Anderson  T. V. Matrosova  P. S. Minyuk  J. Brigham-Grette  M. Melles 《Russian Journal of Pacific Geology》2007,1(6):550-555

The comprehensive study of the upper 1283 cm of sediment from Lake El’gygytgyn, which formed nearly 4 Ma ago following a meteorite impact in northern Chukotka, yielded the first continuous record of the extreme changes in the Beringian climate and vegetation from the middle Middle Pleistocene to recent time (equivalent of marine isotope stages of 1–7 and the upper part of isotope stage 8). During this period, the climate was warmer than at present between 8600 and 10 7000 ¹⁴C years and during the Late Pleistocene (isotope substage 5e, 116–128 ka ago). In 2003, the German-Russian-USA expedition continued studying sediments of Lake El’gygytgyn to obtain new evidence of the change in the vegetation cover in the Middle Pleistocene and the first information on the Middle Pleistocene interglacial (isotope stage 9; 297–347 ka ago). Pollen spectra characterizing the Middle Pleistocene interglacial are similar to spectra of the early stage of the Early Pleistocene interglacial and the climatic optimum in the Pleistocene to Holocene transitional period. The climatic history of Lake El’gygytgyn is basic for stratigraphic interpretations and correlations in the eastern sector of the Arctic. These data also expand our understanding of climatic changes that are studied within the framework of the “Pole-Equator-Pole Paleoclimate,” “Past Global Changes,” and other international projects.  相似文献   

A Look Ahead: Expected Ionospheric Effects on GPS in 2000     

John A. Klobuchar  Patricia H. Doherty 《GPS Solutions》1998,2(1):42-48

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Separation of local and regional information in distorted GDS response functions by hypothetical event analysis   总被引：2，自引：0，他引：2  

Patricia Ritter  Roger J. Banks 《Geophysical Journal International》1998,135(3):923-942

Electromagnetic investigations are usually intended to examine regional structures where induction takes place at a given period range. However, the regional information is often distorted by galvanic effects at local conductivity boundaries. Bahr (1985) and Groom & Bailey (1989) developed a physical distortion model for decomposing the MT impedance tensor, based upon local galvanic distortion of a regional 2-D electromagnetic field. We have extended their method to predict the magnetic variation fields created at an array of sites. The magnetic response functions at periods around 1000 s may be distorted by large-scale inhomogeneities in the upper or middle crust. In this period range, the data measured by a magnetometer array contain common information that can be extracted if the data set is treated as a unit, for example by using hypothetical event analysis. With this technique it is always possible to recover the regional strike direction from distorted data, even if a strong, spatially varying regional vertical field component is present in the data set. The determination of the regional impedance phases, on the other hand, is far more sensitive to deviations from the physical distortion model.
The approach has been used to investigate the Iapetus data set. For the array, which covers an area of 200  km × 300  km in northern England/southern Scotland, the technique revealed a common regional strike azimuth of ca . N125° E in the period range 500–2000  s. This direction differs from the strike indicated by the induction arrows, which seem influenced mainly by local current concentrations along the east–west-striking Northumberland Trough and a NE–SW-striking mid-crustal conductor. Both impedance phases are positive and differ by ca . 10°, which supports the assumptions of distortion fields in the data set and that the regional structure is 2-D.  相似文献   

Coda Q before and after the eruptions of 13 November 1985, and 1 September 1989, at Nevado del Ruiz Volcano, Colombia     

B. John Makario Londoño  A. John Jairo Sanchez  E. Luis Eduardo Toro  Fernando Gil Cruz  Olga Patricia Bohorquez 《Bulletin of Volcanology》1998,59(8):556-561

 Coda Q^–1 was calculated at Nevado del Ruiz Volcano (NRV) before and after two phreatomagmatic eruptions (November 1985, September 1989) and for a period of stability (May 1987) using a functional form for coda derived from a single scattering model (Sato 1977). Substantial changes were found before and after the eruptions. The highest value of Q^–1 was found during the November 1985 eruption, an intermediate value for the September 1989 eruption, and the lowest value for May 1987. It seems that the changes in coda Q^–1 at NRV have a still-unknown relationship with the volume or magnitude of the eruption. A relatively strong frequency dependence was found for all periods. Also Q^–1 clearly changed with time, suggesting that the scattering was strong for the eruption of November 1985 and decreased for the eruption of September 1989, and that the intrinsic absorption probably increased. This suggests the possibility that crystallization is taking place in the NRV magma. The clear change of coda Q^–1 before and after the eruptions at NRV also suggests the possibility that coda Q^–1 is a premonitory tool of activity at this volcano. Received: 25 October 1996 / Accepted: 21 January 1998  相似文献   

The Cepheid period–luminosity zero-point from radial velocities and Hipparcos proper motions     

Michael Feast  Frederic Pont  & Patricia Whitelock 《Monthly notices of the Royal Astronomical Society》1998,298(2):L43-L44

A value for the zero-point (ρ) of the Cepheid period–luminosity relation, <  M _V  >= 2.81 log P  + ρ, is deduced by comparing the value of the Oort constant, A , derived from radial velocities with that derived from Hipparcos proper motions. We find in this way that ρ =−1.47 ± 0.13, in excellent agreement with the value derived from Hipparcos trigonometrical parallaxes, ρ = −1.43 ± 0.10, by Feast &38; Catchpole in a recent paper.  相似文献   

Relative influence of vegetation on urban energy budgets and surface temperatures     

Werner H. Terjung  Patricia A. O'Rourke 《Boundary-Layer Meteorology》1981,21(2):255-263

Two deterministic models were combined: one for canopy leaf energy budgets and one for street canyon energy budgets. The effects of street parks and roof gardens in contrast to non-vegetated city blocks were examined by the use of four typical urban morphologies, which were exposed latitudinally to summer and winter simulations. A variety of increases and decreases in shortwave radiation, net radiation, sensible heat flux, and system reradiation resulted. These changes appear to represent the generalized limits of the possible responses to the addition of vegetation to non-vegetated city blocks.  相似文献   

Ground-Water Lake Relationships and Ground-Water Quality in the Sand Plain Province of Wisconsin—Nepco Lake     

Robert J. Karnauskas  Mary P. Anderson 《Ground water》1978,16(4):273-281

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Geologic assessment of environmental impact in Lake Macatawa,Michigan     

John B. Anderson  Richard Wheeler  Charles P. Dunning  Sue Shepley  Marion Fowke 《Environmental Geology》1978,2(2):67-78

A historical record of the effects of human development upon Lake Macatawa is established using geologic criteria. Significant cultural events are recognized using the pollen record, particularly ambrosia/vesiculate pollen ratios, and occurrences of detrital and chemical contaminants within the more recent sedimentary column. Detrital contaminants include such things as cinder and ash from coal burning power plants and animal hair from early tanning operations. Trace metal contaminants, frequently associated with specific industrial events, are particularly useful in establishing a modern sedimentary chronology. The impact of human activity upon Lake Macatawa is measured using fossil diatoms. The advantage of this method of environmental impact assessment is that it provides a historical perspective in which changes within an environment are related to its natural conditions.  相似文献   

Comparative discharges of fresh and waste water along the California coast     

G. B. Griggs  Patricia A. McCrory 《Environmental Geology》1975,1(2):89-95

As the population of California grows, the discharge of domestic and industrial waste water and power-plant cooling water into coastal waters continuously increases. About 0.75 × 10⁶ m³ of industrial waste water, 3.75 × 10⁶ m³ of domestic waste water, and 26.5 × 10⁶ m³ of thermal effluent are discharged daily into California's nearshore waters. These waters do not have an infinite capacity to break down and disperse the pollutants. Waste water discharged near shore may remain there for considerable time and have a significant effect on water quality and marine life. The low population and wet climate of the northern coastal region have led to small discharges of waste water but very large inputs of fresh water to the ocean. Southward along the Pacific Coast the climate becomes more arid, and population increases. This combination leads to a large excess of waste-water over fresh-water discharge. Many individual waste-water discharges exceed the average daily discharge of most of the rivers which enter the coastal waters.  相似文献   

Studies in diffusion,II. Oxygen in phlogopite mica     

B.J. Giletti  T.F. Anderson 《Earth and Planetary Science Letters》1975,28(2):225-233

Self-diffusion of oxygen in a natural phlogopite mica (annite 4%) has been measured under hydrothermal conditions at 2000 bars pressure and from 500 to 800°C using water enriched in¹⁸O. Diffusional transport is dominantly parallel to the c crystallographic axis. A linear Arrhenius plot was obtained with a pre-exponential term = (1.03 ± 0.38) × 10^?9cm²sec^?1 a and an activation energy of 29 ± 2kcal/g-atom O. The difference in transport rate between oxygens in the OH groups and those in tetrahedral sites is small to non-existent unless the OH oxygens diffuse much more slowly than the other oxygens, which we consider unlikely. A typical phlogopite crystal, 0.2 mm thick by 1 mm across will lose radiogenic argon faster than it will exchange oxygen at temperatures above 435°C, but the reverse holds at lower temperatures if the diffusion mechanism can be extrapolated to temperatures below 500°C. Such a crystal will lose only 5% of its argon if held at 380°C for 1 m.y., but could exchange 27% of its oxygen in that time. The rate at which phlogopite will undergo deformation by diffusional creep does not appear to be controlled by oxygen diffusion.  相似文献