The Greenland Ice Core Chronology 2005, 15–42 ka. Part 1: constructing the time scale     

Katrine K. Andersen  Anders Svensson  Sigfus J. Johnsen  Sune O. Rasmussen  Matthias Bigler  Regine Rthlisberger  Urs Ruth  Marie-Louise Siggaard-Andersen  Jrgen Peder Steffensen  Dorthe Dahl-Jensen  Bo M. Vinther  Henrik B. Clausen 《Quaternary Science Reviews》2006,25(23-24):3246

The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na⁺, Ca²⁺, SO₄²⁻, NO₃⁻, NH₄⁺. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ¹⁸O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05.  相似文献   

Women in agriculture: advocates for a gendered sustainable agriculture     

Ruth Liepins 《The Australian geographer》1995,26(2):118-126

A gendered consideration of rural geography has been barely discernible within Australian and New Zealand literature. The notable exceptions in this case have illustrated the complexity and merit of studying the gender patterns and relations of rural life. Outside geography, there is an expanding literature on rural women in Australia. These works parallel significant developments in the lives and politics of rural and agricultural women themselves. This paper reports selected findings from a study of the women in agriculture movement in Australia. As such, it illustrates the increased awareness of the gendered conditions of farming. The women in agriculture movement works to increase the recognition of women's contribution to agriculture. In doing so it affirms the legitimacy of women farmers’ voices and perspectives. There will be no sustainable rural systems while half the rural population is unseen or unheard. Women in agriculture demonstrate a social dimension of sustainability. They highlight the need to integrate gender equity and a ‘wider‐than‐economic’ conceptualisation of sustainable agriculture. Their actions can stimulate rural geographers to further consider the social and political aspects of rural sustainability beyond the conventional farm/industry and community service sites we usually consider.  相似文献   

Biological marker distribution in coexisting kerogen, bitumen and asphaltenes in Monterey Formation diatomite, California     

Tannenbaum E  Ruth E  Huizinga BJ  Kaplan IR 《Organic Geochemistry》1986,10(1-3 PT 1):531-536

Organic-rich (18.2%) Monterey Formation diatomite from California was studied. The organic matter consist of 94% bitumen and 6% kerogen. Biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter. While 17 alpha(H), 18 alpha(H), 21 alpha(H)-28,30-bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes, it was not detected in the pyrolysates of the kerogen. A C40-isoprenoid with "head to head" linkage, however, was present in pyrolysates of both kerogen and asphaltenes, but not in the bitumen from the diatomite. The maturation level of the bitumen, based on the extent of isomerization of steranes and hopanes, was that of a mature oil, whereas the pyrolysate from the kerogen showed a considerably lower maturation level. These relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock. We consider the possibility, however, that some of the 28,30-bisnorhopane-rich Monterey Formation oils have not been generated through thermal degradation of kerogen, but have been expelled from the source rock at an early stage of diagenesis.  相似文献   

Overestimating the coronal density and its effect on the velocities derived from Lα Doppler dimming     

Ruth Esser  Shadia R. Habbal 《Solar physics》1993,147(2):241-254

It is shown that relatively small errors of the order of 10% in the electron densities, for example derived from polarization brightness measurements, might lead to large errors in the velocities inferred from intensity measurements of the L Hi 1216 spectral line in the inner corona. It is demonstrated that in some cases this effect can result in very high velocities close to the coronal base with subsequent small acceleration with heliocentric distance. It is also pointed out that the errors in the deduced velocities can be reduced if simultaneous observations that place constraints on the mass flux are available, and by ensuring that the mass flux computed from the derived velocities and densities is constant.  相似文献   

Long-term changes in salt marsh extent affected by channel deepening in a modified estuary   总被引：2，自引：0，他引：2  

Ruth Cox  R. A. Wadsworth  A. G. Thomson 《Continental Shelf Research》2003,23(17-19):1833

The aim of this study is to quantify the long-term (54 years) rates of marsh extension and retreat at two sites in the Westerschelde Estuary, SW Netherlands. Nine sets of aerial photographs were obtained for each of the two salt marsh sites, Zuidgors and Waarde, taken at various times between 1944 and 1998. The seaward edges of the marshes were digitised from rectified images after the photographs had been scanned and georegistered to the Dutch National Grid. Comparison of the extents of the marshes at these nine time points revealed that the areas of both marshes had fluctuated during these 54 years with periods of both extension and retreat of the seaward marsh edges. These periods of extension and retreat appeared to be approximately synchronised until the 1990s, with mean changes in position of marsh front ranging from −7.92 to 6.04 m a⁻¹.The rate of landward retreat and seaward extension of the marsh front is shown to be related to an increase in the tidal prism brought about by dredging operations to maintain or increase the depth of the main navigable channel of the estuary. The consequent greater frequency with which the high tides reach the edge of the fringing marshes increases the risk of erosion. Strong westerly winds may also be a factor in increasing erosion. No relationship between the volume of shipping traffic using the estuary and marsh erosion was found.  相似文献   

Acceptance of the 2002 F. W. Clarke Award     

Ruth Elaine Blake 《Geochimica et cosmochimica acta》2003,67(13):2315-2316

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Geometrical relationships between unconformities and subsequent folding: the Arro fold system (southern Pyrenees)Relations entre discordances et plissement dans le système de plis et chevauchements d'Arro (bassin de Graus-Tremp,Pyrénées)     

Antonio M Casas  Ruth Soto  Begoña Martı́nez-Peña 《Comptes Rendus Geoscience》2002,334(10):765-772

The Arro system is an oblique fold system involving the Eocene sediments of the Graus-Tremp basin. It consists of westward-verging folds, trending NNW–SSE, some of them related with thrusts, in piggyback sequence. Seismic profiles allow to infer the geometry of structures at depth: folds and thrusts are ‘decolled’ over an unconformity between turbiditic and platform sediments. Re-activation of bedding surfaces by folding in the underlying units resulted in folding and thrusting in the upper series. To cite this article: A.M. Casas et al., C. R. Geoscience 334 (2002) 765–772.  相似文献   

Social Geographies. Space and Society     

Ruth Panelli 《New Zealand geographer》2002,58(1):57-58

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Alpine Ecosystems of Northwest Yunnan, China： an Initial Assessment for Conservation   总被引：1，自引：1，他引：0  

Ruth Sherman Renee Mullen LI Haomin FANG Zhendong WANG Yi 《山地科学学报》2007,4(3):181-192

Implementing conservation actions on-the-ground is not a straightforward process,especially when faced with high scientific uncertainty due to limited available information. This is especially acute in regions of the world that harbor many unique species that have not been well studied,such as the alpine zone of the Hengduan Mountains of Northwest Yunnan (NWY),a global biodiversity hotspot and site of The Nature Conservancy’s Yunnan Great Rivers Project. We conducted a quantitative,but rapid regional-level assessment of the alpine flora across NWY to provide a broad-based understanding of local and regional patterns of the alpine flora,the first large-scale analysis of alpine biodiversity patterns in this region. Multivariate analyses were used to classify the major plant community types and link community patterns to habitat variables. Our analysis indicated that most species had small distributions and/or small population sizes. Strong patterns emerged with higher diversity in the more northern mountains,but beta diversity was high,averaging only 10% among sites. The ordinations indicated that elevation and geographic location were the dominant environ-mental gradients underlying the differences in the species composition among communities. The high beta diversity across the alpine of these mountains implies that conservation strategies ultimately will require the protection of large numbers of species over a large geographical area. However,prioritiza-tion should be given to areas where potential payoffs are greatest. Sites with high species richness also have a greater number of endemic species,and,by focusing efforts on these sites,conservation investments would be maximized by protecting the greatest number of unique species.  相似文献   

Deforesting the Earth: from prehistory to global crisis: an abridgement - by Michael Williams     

Ruth DeFries 《Area》2007,39(3):410-411

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