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41.
Elizabeth A. V. Mackie Jeremy M. Lloyd Melanie J. Leng Michael J. Bentley Carol Arrowsmith 《第四纪科学杂志》2007,22(6):579-591
Carbon isotopes (δ13C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ13C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ13C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ13C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO2 concentration, poor vegetation development and temperature influence δ13C values during this period. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
42.
Nicholas R. Golledge Derek Fabel Jeremy D. Everest Stewart Freeman Steven Binnie 《第四纪科学杂志》2007,22(8):785-791
We use cosmogenic 10Be surface exposure age techniques at a locality close to Rannoch Moor, western Scottish Highlands, in order to establish the age and chronology of its most recent glaciation. Glacial erratics and an in situ bedrock quartz vein sampled from this site—the summit of Beinn Inverveigh—have yielded zero‐erosion exposure ages of 12.9 ± 1.5 ka to 11.6 ± 1.0 ka, implying complete ice cover of the mountain during the Younger Dryas, or Loch Lomond Stadial. These results fit closely with published 14C dates that bracket the maximum (lateral) extent of ice cap outlet glaciers, and are the first internally consistent ages to specifically address this period of glaciation in Scotland. Furthermore, the dates imply that previous palaeoglaciological reconstructions for this area may have underestimated both the thickness of the former ice cap and, by implication, its volume. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd. 相似文献
43.
Spring snow melt run‐off in high latitude and snow‐dominated drainage basins is generally the most significant annual hydrological event. Melt timing, duration, and flow magnitude are highly variable and influence regional climate, geomorphology, and hydrology. Arctic and sub‐arctic regions have sparse long‐term ground observations and these snow‐dominated hydrologic regimes are sensitive to the rapidly warming climate trends that characterize much of the northern latitudes. Passive microwave brightness temperatures are sensitive to changes in the liquid water content of the snow pack and make it possible to detect incipient melt, diurnal melt‐refreeze cycles, and the approximate end of snow cover on the ground over large regions. Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer for EOS (AMSR‐E) passive microwave brightness temperatures (Tb) and diurnal amplitude variations (DAV) are used to investigate the spatial variability of snowmelt onset timing (in two stages, ‘DAV onset’ and ‘melt onset’) and duration for a complex sub‐arctic landscape during 2005. The satellites are sensitive to small percentages of liquid water, and therefore represent ‘incipient melt’, a condition somewhat earlier than a traditional definition of a melting snowpack. Incipient melt dates and duration are compared to topography, land cover, and hydrology to investigate the strength and significance of melt timing in heterogeneous landscapes in the Pelly River, a major tributary to the Yukon River. Microwave‐derived melt onset in this region in 2005 occurred from late February to late April. Upland areas melt 1–2 weeks later than lowland areas and have shorter transition periods. Melt timing and duration appear to be influenced by pixel elevation, aspect, and uniformity as well as other factors such as weather and snow mass distribution. The end of the transition season is uniform across sensors and across the basin in spite of a wide variety of pixel characteristics. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
44.
Mark Cropper Silvia Zane Roberto Turolla Luca Zampieri Matteo Chieregato Jeremy Drake Aldo Treves 《Astrophysics and Space Science》2007,308(1-4):161-166
We report XMM-Newton observations of the isolated neutron star RBS1774 and confirm its membership as an XDINS. The X-ray spectrum is best fit
with an absorbed blackbody with temperature kT=101 eV and absorption edge at 0.7 keV. No power law component is required. An absorption feature in the RGS data at 0.4 keV
is not evident in the EPIC data, but it is not possible to resolve this inconsistency. The star is not seen in the UV OM data
to m
AB
∼21. There is a sinusoidal variation in the X-ray flux at a period of 9.437 s with an amplitude of 4%. The age as determined
from cooling and magnetic field decay arguments is 105–106 yr for a neutron star mass of 1.35–1.5 M⊙.
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47.
Bhoopesh Mishra Maxim Boyanov Shelly D. Kelly Jeremy B. Fein 《Geochimica et cosmochimica acta》2010,74(15):4219-9603
Bulk Cd adsorption isotherm experiments, thermodynamic equilibrium modeling, and Cd K edge EXAFS were used to constrain the mechanisms of proton and Cd adsorption to bacterial cells of the commonly occurring Gram-positive and Gram-negative bacteria, Bacillus subtilis and Shewanella oneidensis, respectively. Potentiometric titrations were used to characterize the functional group reactivity of the S. oneidensis cells, and we model the titration data using the same type of non-electrostatic surface complexation approach as was applied to titrations of B. subtilis suspensions by Fein et al. (2005). Similar to the results for B. subtilis, the S. oneidensis cells exhibit buffering behavior from approximately pH 3-9 that requires the presence of four distinct sites, with pKa values of 3.3 ± 0.2, 4.8 ± 0.2, 6.7 ± 0.4, and 9.4 ± 0.5, and site concentrations of 8.9(±2.6) × 10−5, 1.3(±0.2) × 10−4, 5.9(±3.3) × 10−5, and 1.1(±0.6) × 10−4 moles/g bacteria (wet mass), respectively. The bulk Cd isotherm adsorption data for both species, conducted at pH 5.9 as a function of Cd concentration at a fixed biomass concentration, were best modeled by reactions with a Cd:site stoichiometry of 1:1. EXAFS data were collected for both bacterial species as a function of Cd concentration at pH 5.9 and 10 g/L bacteria. The EXAFS results show that the same types of binding sites are responsible for Cd sorption to both bacterial species at all Cd loadings tested (1-200 ppm). Carboxyl sites are responsible for the binding at intermediate Cd loadings. Phosphoryl ligands are more important than carboxyl ligands for Cd binding at high Cd loadings. For the lowest Cd loadings studied here, a sulfhydryl site was found to dominate the bound Cd budgets for both species, in addition to the carboxyl and phosphoryl sites that dominate the higher loadings. The EXAFS results suggest that both Gram-positive and Gram-negative bacterial cell walls have a low concentration of very high-affinity sulfhydryl sites which become masked by the more abundant carboxyl and phosphoryl sites at higher metal:bacteria ratios. This study demonstrates that metal loading plays a vital role in determining the important metal-binding reactions that occur on bacterial cell walls, and that high affinity, low-density sites can be revealed by spectroscopy of biomass samples. Such sites may control the fate and transport of metals in realistic geologic settings, where metal concentrations are low. 相似文献
48.
Gosselin Jeremy M. Dosso Stan E. Askan Aysegul Wathelet Marc Savvaidis Alexandros Cassidy John F. 《Journal of Seismology》2022,26(4):781-821
Journal of Seismology - Seismic site characterization attempts to quantify seismic wave behavior at a specific location based on near-surface geophysical properties, for the purpose of mitigating... 相似文献
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50.
Minghu DING Wei HAN Tong ZHANG Xiaoyuan YUE Jeremy FYKE Ge LIU Cunde XIAO 《大气科学进展》2020,37(5):494-504
The variation in the precipitation phase in polar regions represents an important indicator of climate change and variability.We studied the precipitation phase at the Great Wall Station and Antarctic Peninsula(AP)region,based on daily precipitation,synoptic records and ERA-Interim data during the austral summers of 1985?2014.Overall,there was no trend in the total precipitation amount or days,but the phase of summer precipitation(rainfall days versus snowfall days)showed opposite trends before and after 2001 at the AP.The total summer rain days/snow days increased/decreased during 1985?2001 and significantly decreased at a rate of?14.13 d(10 yr)?1/increased at a rate of 14.31 d(10 yr)?1 during 2001?2014,agreeing well with corresponding variations in the surface air temperature.Further,we found that the longitudinal location of the Amundsen Sea low(ASL)should account for the change in the precipitation phase since 2001,as it has shown a westward drift after 2001[?41.1°(10 yr)?1],leading to stronger cold southerly winds,colder water vapor flux,and more snow over the AP region during summertime.This study points out a supplementary factor for the climate variation on the AP. 相似文献