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91.
Regional modelling of permafrost thicknesses over the past 130 ka: implications for permafrost development in Great Britain
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Jonathan P. Busby Jonathan R. Lee Sev Kender Paul Williamson Simon Norris 《Boreas: An International Journal of Quaternary Research》2016,45(1):46-60
The greatest thicknesses of permafrost in Great Britain most likely occurred during the last glacial–interglacial cycle, as this is when some of the coldest conditions occurred during the last 1 000 000 years. The regional development of permafrost across Great Britain during the last glacial–interglacial cycle was modelled from a ground surface temperature history based on mean annual temperatures and the presence of glacier ice. To quantify the growth and decay of permafrost, modelling was undertaken at six locations across Great Britain that represent upland glaciated, lowland glaciated, upland unglaciated and lowland unglaciated conditions. Maximum predicted permafrost depths derived in this academic study range between several tens of metres to over 100 m depending upon various factors including elevation, glacier ice cover, geothermal heat flux and air temperature. In general, the greatest maximum permafrost thicknesses occur at upland glaciated locations, with minimum thickness at lowland sites. Current direct geological evidence for permafrost is from surface or shallow processes, mainly associated with the active layer. Further research is recommended to identify the imprint of freeze/thaw conditions in permanently frozen porous rocks from beneath the active layer. 相似文献
92.
Richard A. Staff Takeshi Nakagawa Gordon Schlolaut Michael H. Marshall Achim Brauer Henry F. Lamb Christopher Bronk Ramsey Charlotte L. Bryant Fiona Brock Hiroyuki Kitagawa Johannes van der Plicht Rebecca L. Payne Victoria C. Smith Darren F. Mark Alison Macleod Simon P. E. Blockley Jean‐Luc Schwenninger Pavel E. Tarasov Tsuyoshi Haraguchi Katsuya Gotanda Hitoshi Yonenobu Yusuke Yokoyama Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266
The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range). 相似文献
93.
Sébastien Gac Ritske S. Huismans Nina S. C. Simon Yuri Y. Podladchikov Jan Inge Faleide 《地学学报》2013,25(6):459-464
The origin of large subsidence in intracratonic basins is still under debate. We propose a new and self‐consistent model for the formation of those basins, where lithospheric shortening/buckling triggers metamorphism and densification of crustal mafic heterogeneities. We use a forward thermo‐mechanical finite element technique to evaluate this mechanism for the typical example of the East Barents Sea basin (EBB) where a very large and compensated subsidence, accommodating an up to 20‐km‐thick sediment succession, is observed. The lower crust in the dynamic model is modelled with petrologic‐consistent densities for a wet mafic gabbroic composition that depend on pressure and temperature taking into account dehydration at high PT conditions. The model successfully explains the main characteristics of the EBB, notably the large anomalous and fast subsidence during the Late Permian–Early Triassic, its present‐day geometry and the absence of a significant gravity anomaly. 相似文献
94.
The Kaluvelly watershed is a coastal area (Tamil Nadu, India) where water abstraction has resulted in a dramatic fall in the level of the water table and a piezometric depression in the most exploited aquifer, the Vanur aquifer. In addition, intensification/mechanization of agriculture may have affected the quality of recharge water. An initial hydrodynamic study showed that the Vanur aquifer is highly vulnerable to salinization due to potential seawater intrusion, and our aim was to determine the source of salinity recorded in the groundwater of this multilayered aquifer. Our approach involved the use of existing boreholes and of a moderate number of samples, with the aim of developing appropriate water resource management techniques. Major element, 18O/16O, 2H/1H and 87Sr/86Sr, ratios were measured in rainwater, surface water and groundwater collected during five sampling campaigns over a 2‐year period. Geochemical data indicate that the Vanur aquifer is recharged and that small mixings between aquifers fluctuate according to monsoon intensity. There was no evidence of seawater intrusion. The range of recorded salinity originated mainly from water–rock interaction but a disconnection of some deeper parts of the aquifer was apparent. Strontium isotopic ratios in the recharge area suggest an anthropogenic influence, possibly related to fertilizer use. A high SO4/Cl ratio was observed in the aquifer; in the deeper parts, the influence of a formation containing lignite is hypothesized, whereas near the surface, sulphate may partly originate from fertilizer use and fossil fuel combustion. Water isotopic data suggest that the origin of precipitation in this region has been unchanged for several hundreds or thousands of years. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
95.
Nathalie van Vliet Ole Mertz Andreas Heinimann Tobias Langanke Unai Pascual Birgit Schmook Cristina Adams Dietrich Schmidt-Vogt Peter Messerli Stephen Leisz Jean-Christophe Castella Lars Jørgensen Torben Birch-Thomsen Cornelia Hett Thilde Bech-Bruun Amy Ickowitz Kim Chi Vu Kono Yasuyuki Jefferson Fox Christine Padoch Alan D. Ziegler 《Global Environmental Change》2012,22(2):418-429
This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems. 相似文献
96.
Simon A. T. Redfern Ann Graeme-Barber Ekhard Salje 《Physics and Chemistry of Minerals》1988,16(2):157-163
The lattice parameters of anorthites An98Ab2 and An100 have been measured from 22 to 1100 K. The spontaneous strain arising from the \(I\overline 1 - P\overline 1\) displacive transition in An98 follows second order Landau behaviour. The spontaneous strain (? s) couples quadratically to the order parameter (Q 0) with ? s∝Q 02∝(T c * ?T) and T c * =530 K in An98. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which Al/Si order and Na content renormalize the fourth order coefficient. 相似文献
97.
M S Narayanan P K Pal P C Joshi M Mali Baby Simon 《Journal of Earth System Science》1989,98(3):247-254
Water vapour tracers can provide useful information on winds at ≈ 500mb by observing the 6·7μ radiances. This fills the data
gap in the cloud motion winds provided by conventional meteorological geostationary satellites. There is no geostationary
satellite at present over the Indian Ocean with 6·7μ imaging capability to provide mid-tropospheric winds. The potentials
of 6·7μ radiances, available from polar orbiting satellites, for mid-tropospheric circulation features have been examined
in this study. Tiros-N satellite data of May 1979 and ECMWF level-IIIb wind data were analysed to relate the radiances with
the streamlines. We find that the radiances of 6·7μ from orbiting satellites agree well with the wind field. 相似文献
98.
P. C. Simon D. Gillotay N. Vanlaethem-Meuree J. Wisemberg 《Journal of Atmospheric Chemistry》1988,7(2):107-135
Absorption cross-sections of nine halomethanes (CCl4, CHCl3, CH2Cl2, CH3Cl, CFCl3, CF2Cl2, CF3Cl, CHFCl2, and CHF2Cl), measured between 174 and 250 nm for temperatures ranging from 225 to 295 K, are presented with uncertainties ranging from 2 to 4% and compared with previous determinations made for comparable temperature ranges.The largest temperature effect which takes place near the absorption threshold, decreases the absorption cross-section up to 50% for highly chlorinated methanes, but is negligible for molecules highly stabilized by hydrogen and/or fluorine. Extrapolated values for temperatures of aeronomical interest are presented, as well as parametrical formulas which give absorption cross-section values for given wavelength and temperature ranges. 相似文献
99.
The available data on known reserves of extracted resources have not previously been tabulated and graphed. In this article we compile the reserves data in one place for the first time. This serves to (1) show the trends in the reserves series, (2) make the series available to others, and (3) place the reserves data in the context of price data for which longer series have been available, and with which they can now be seen to be consistent in both showing increasing availability rather than increasing scarcity. 相似文献
100.