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1.
2.
High levels of Cd and Zn in Jamaican soils observed in geochemical surveys are related to the presence of phosphorites of possible Late-Miocene or Pliocene age. The trace element and REE geochemistry of the phosphorites, together with SEM studies, indicate a guano origin for the phosphorites. No specific host minerals for Cd could be identified in the fossiliferous phosphorite which is characterized by uniquely high levels of Cd, Zn, Ag, Be, U and Y. However, in the soil Cd is present in lithiophorite and a complex history of pedological development is preserved in the aluminous–goethite present in the soil. The unique guano signature is preserved in the soil despite the fact that guanos themselves have either not been observed or have been destroyed by continuing karst and soil development. The phosphorite geochemical signature can be traced in the data of a 1988 island-wide soil geochemical survey, identifying areas where the Palaeo-environment that supported bird ‘rookeries’ existed in the Late-Miocene or Pliocene. 相似文献
3.
A complexometric titration technique was employed to measure the total capacity of a variety of marine organisms to adsorb Cu2+. Measured adsorption capacities were 0.22 meq g−1 for phytoplankton, 0.3–1.0 meq g−1 for macrophytes, 1.0–2.5 meq g−1 for zooplankton and 0.3 meq g−1 for suspended particulate matter. The capacity of these materials to adsorb Cu2+ was reduced significantly in the presence of Mg2+ at seawater concentrations. Competition between Mgt2+ and Cu2+ for adsorption sites at pH 6 is described by an average conditional equilibrium constant of 103.7. This constant is such that very little Cu2+ may be adsorbed onto particulates and marine phytoplankton in the presence of Mg2+. Further, primary productivity data and estimates of the detrital carbon sedimentation in Long Island Sound suggest that the flux of particulate carbon is insufficient to remove significant amounts of Cu from the water column to sediments by adsorption mechanisms. 相似文献
4.
During the 1972 apparition of Jupiter, we carried out a patrol of the (3,0) S(1) and (4,0) S(1) quadrupole lines of molecular hydrogen in the equatorial region and in bands bounded by ±15 and ±49° zenographic latitude from the McDonald and Table Mountain Observatories. At the center of the Jovian disk, we found evidence of temporal variability of both lines over the duration of our observing period. We employ a technique which takes into account all radiative transfer processes in an inhomogeneous model of Jupiter's atmosphere, and use it to derive the effective level of formation of the spectral lines and the relative abundance of hydrogen. In this way, we are able to correlate measured changes in the equivalent widths of the hydrogen lines with variations in cloud structure. The effective pressure level at which the (4,0) S(1) line is formed varies in the range 2 ± 0.5 to 1.3 ± 0.2 atm, while for the (3,0) S(1) line, the pressure varies between 1.6 ± 0.5 and 1 ± 0.4 atm. If these variations are interpreted in terms of changes in elevation of the top of a dense lower cloud deck, the elevation apparently varied with an amplitude of 25 km during the observational period.Spatial variations in the strengths of both lines were also found. Both lines are weaker at the east limb than at the center of the disk (15–19%) while the variations toward the west limb are less pronounced (5%). Similar center-to-limb variations were found in the latitude bands bounded by ±15 and ±49°, although the lines were stronger in the northern component at the time of the observations. 相似文献
5.
The downhole vertical accelerometer array VSAP near Paducah, KY, consists of three-component accelerometers at the surface, the top of the McNairy Formation (−41 m), and the top of the Paleozoic bedrock (—99 m). The array is at the northern end of the Mississippi Embayment, and it was installed to verify the ground-motion modeling for the site, assuming a significant earthquake in the New Madrid Seismic Zone. Accelerograms from 4.2 and 2.0 mb earthquakes were used to check aspects of the modeling pertaining to linear behavior of the soil column, and to review the soil column models derived by drilling and geotechnical methods and through the use of high-resolution P- and SH-wave seismic refraction in reflection techniques. Results of the study indicate that for the linear case the soil column models derived by the two techniques are equivalent, and that the most important boundary in the soil column, with respect to amplification of the ground motions, is the interface between the limestone bedrock and soil. 相似文献
6.
This paper describes palynological evidence for what appears to be comparatively large-scale human impact in the catchment of the Sungai Niah in the wet tropical lowland swamp forests of Sarawak, Malaysian Borneo close to the Great Cave of Niah. Pollen associated with cleared landscapes and rice cultivation is evident in the sedimentary record from before 6000 cal yr B.P. Human activity seems to have been associated with changes in sedimentary regime, with peat-dominated environments being replaced diachronously by clay-dominated deposition. This may reflect anthropogenic soil erosion in the catchment of the Sungai Niah. 相似文献
7.
Naturally-occurring drought is defined here to be drought arising from the nonlinear interactions which are an inherent part of the dynamics of the climatic system. As such it has no specific excitation mechanism, in contrast to forced drought where sea surface temperature anomalies are frequently cited as an important precursor. The essential difference between these two types of drought is that the former is very local and isolated spatially, whereas the latter is widespread and coherent. Observations for Australia are used to illustrate these points. Results are given for a 10-year general circulation model integration which clearly simulated naturally occurring drought and highlighted its unique characteristics. Multi-annual time series for specific geographical regions in the model show that no differences in monthly mean values of relative humidity or zonal and meridional fluxes of moisture were apparent for years with or without drought. More detailed analysis indicated that rather small differences exist in atmospheric temperatures and absolute humidities between drought and nondrought years which are important factors in determining the onset of precipitation in the model.Overall the analysis emphasises the subtlety of the processes involved. These processes, however, were able to produce completely different precipitation histories from one year to the next at a given point. The smallness of the changes involved in the atmospheric processes indicates that the nonlinearities were able to modulate conditions at a given point within an existing synoptic system only slightly, rather than initiate a new climatic regime in drought years. The problem of naturally-occurring drought, of course, is that it is intrinsically unpredictable. 相似文献
8.
Soft-shell clams (Mya arenaria) can serve important ecological roles in intertidal mudflats and are an important economic and recreational resource in the northwestern Atlantic. However, environmental factors affecting newly-settled and juvenile clam abundances within a given settlement season remain uncertain. We conducted a field study assessing relationships between juvenile soft-shell clam abundance and spatial, temporal, and environmental variables in coastal mudflats of the northern shore of the Bay of Fundy. Sediment pH and low-tide water temperature (tide pools) were monitored in situ on a biweekly–monthly basis over the course of the M. arenaria settlement season in 2012 at four study sites to quantify diel variation in sediment pH and temperature. Core samples were also collected to quantify M. arenaria (<6 mm) abundance. Sea-surface and air temperature, and in situ sediment pH and water temperature were then used to predict clam abundance. Sediment pH was spatially and temporally variable, while in situ temperature was stable and declined over the sampling season. Akaike’s information criterion model selection indicated that models incorporating site, date, and air temperature best predicted 2012 recruitment patterns in linear models when all variables were included. When only environmental variables were included, the best linear model included minimum air temperature and sediment pH. When data were averaged across dates for each site to remove potential temporal effects, mean clam abundance displayed a significant positive relationship with sediment pH and sediment grain size, but not minimum air temperature. The results of this study suggest that sediment pH and/or sediment grain size may influence within-season juvenile soft-shell clam abundances across mudflats in the Bay of Fundy. Field experiments at the same (or similar) sites are now needed to confirm the mechanism driving the observed relationships. 相似文献
9.
Evaluation of biotite-garnet geothermometers: application to the English River subprovince,Ontario 总被引:1,自引:0,他引:1
In recent years, there have been numerous calibrations of the biotite-garnet Fe-Mg exchange geothermometer. The Eastern Lac Seul region of the English River subprovince, Ontario, provides an excellent field area in which to compare these calibrations.Trend surface analysis using the temperatures obtained from garnet cores and matrix biotites-showed almost identical trends in the eastern Lac Seul region regardless of the calibration used. The absolute temperatures and the precision of each calibration do, however, show large variation. Geothermometers based solely on lnKD were found to give more precise results than the calibrations that attempt to incorporate non-Fe-Mg components. The Perchuk and Lavrent'eva (1983) thermometer yields the most precise and accurate results. If a sufficient number of samples are collected over a region, it can be used to estimate metamorphic temperature trends to ±30° C. Metamorphism and migmatization of the English River subprovince occurred during the Kenoran orogeny, 2.68 b.y. ago. Our results show that a thermal anticline has been preserved, with temperatures of 600° C at the north and south contacts with Uchi and Wabigoon Greenstone belts, increasing to 725 °C at the center of the subprovince. A garnet-cordierite in isograd occurs at 650° C and an orthopyroxene in isogradat 700° C. 相似文献
10.
Rock-magnetic proxies of climate change in the loess-palaeosol sequences of the western Loess Plateau of China 总被引:5,自引:0,他引:5
Christopher P. Hunt Subir K. Banerjee Jiamao Han Peter A. Solheid Eric Oches Weiwei Sun Tungsheng Liu 《Geophysical Journal International》1995,123(1):232-244
Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining-one of the few palaeoclimate sites in the currently arid western Loess Plateau of China-illustrate the importance of making many types of rock-magnetic measurements other than susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentration and mineralogy of the magnetic fraction.
The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. the resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. the data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites.
In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records. 相似文献
The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. the resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. the data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites.
In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records. 相似文献