Comparison of palynomorph assemblages from the Cretaceous/Tertiary boundary interval in Western Europe, northwest Africa and southeast China     

Zhichen Song  Fei Huang 《Cretaceous Research》1997,18(6):865-871

The composition of palynomorph assemblages from selected sections through the Cretaceous/Tertiary (K/T) boundary interval in Western Europe, northwest Africa and China is discussed. Similarities are emphasised and widespread trends noted, including the evolutionary development of the porate group of pollen grains, palynomorph extinctions within the boundary interval, and links with a climatic cooling trend. The comparative analysis revealed numerous taxonomic and nomenclature problems, as a list of 71 forms recorded from five papers on European and North African topics demonstrates. These taxa are considered to be similar or identical to palynomorphs documented in four Chinese papers, despite the fact that almost all of the identifications differ at either generic or specific level, or both.  相似文献   

Ecopath, Ecosim, and Ecospace as tools for evaluating ecosystem impact of fisheries   总被引：23，自引：10，他引：23  

Pauly  Daniel; Christensen  Villy; Walters  Carl 《ICES Journal of Marine Science》2000,57(3):697-706

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The benthic communities of the Snorre field in the Northern North Sea (61°30′ N 2°10′ E): 1. The distribution and structure of communities in undisturbed sediments     

Thomas H. Pearson  Hans-Petter Mannvik  Rosalie Evans  Stig Falk-Petersen 《Journal of Sea Research》1996,35(4):301-314

The fauna of the Snorre oil field is diverse and varies along a 40 m depth gradient across the area. Abundance and species richness increase with increasing depth but diversity is highest in the centre of the gradient. The communities present differ widely from those of the adjacent but shallower Statfjord, Gullfaks and Tordis Fields and from the major communities found throughout much of the northern North Sea, a fact attributable to the greater depth, finer sediments, higher sediment organic levels and position on the western slope of the Norwegian Trench. They have greater affinities with the communities in the Troll Field, 85 km SE on silt/clay sediments in the floor of the trench and the Heidrun Field, situated approximately 390 km N at similar depths and in an area of similar sedimentary composition. However the Snorre communities have a much higher number of suspension feeding and surface deposit feeding organisms than either of these other areas. This might be caused by higher current speeds in the Snorre area which could create favourable conditions for suspensivores. Such water movements might bring occasional incursions of intermediate Norwegian Sea water into the area. Indeed the Snorre fauna appears to bear some relationships to the intermediate depth faunas of the Norwegian Sea, and is clearly different from most of the better described northern North Sea faunas.  相似文献   

Map Comparison or Traditional Mass-balance Measurements: Which Method is Better?     

Gunnar Østrem  & Nils Haakensen 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):703-711

A number of Norwegian glaciers were selected in the 1960s for long-term mass-balance measurements, to produce necessary hydrological information for hydropower exploitation. Special large-scale glacier maps were produced for field work and data processing, and some glaciers have been mapped more than once. Thus, comparison of glacier maps can be used to calculate changes in glacier volume for some of the glaciers, provided they are of sufficient accuracy.
Conventional mass-balance measurements were carried out on all the selected glaciers. A cumulative calculation of net balances for a series of years is used to indicate the change in a glacier's volume during that period. However, various errors originate in the field, some of which are systematic, particularly on glaciers with large winter accumulation.
The present study indicates that certain errors are difficult to define and determine, For the maritime glacier Ålfotbreen, a cumulative mass-balance calculation gives a positive total balance (+3.4 m water equivalent in the period 1968–88), whereas the map comparison indicates a total negative balance (−5.8 m water equivalent). This indicates a discrepancy between the methods, which must be accounted for.
Determination of errors in mass-balance measurements is difficult. Sinking of stakes in the accumulation area and the use of sounding sticks (steel probes) in heavy snowlayers cause problems.  相似文献   

Probing the high latitude ionosphere from ground-based observations: The state of current knowledge and capabilities during IPY (2007–2009)     

Lucilla Alfonsi  Andrew J. Kavanagh  Ermanno Amata  Pierre Cilliers  Emilia Correia  Mervyn Freeman  Kirsti Kauristie  Ruiyuan Liu  Juha-Pekka Luntama  Cathryn N. Mitchell  G.A. Zherebtsov 《Journal of Atmospheric and Solar》2008,70(18):2293-2308

During the International Polar Year (IPY), one area of great interest is co-coordinated, multi-instrument probing of the ionosphere at high latitudes. This region is important not only for the applications that rely upon our understanding of it, but also because it contains the footprints of processes that have their origin in the interplanetary space. Many different techniques are now available for probing the ionosphere, from radar measurements to the analysis of very low frequency (VLF) wave paths. Combining these methods provides the ability to study the ionosphere from high in the F-region to the bottom of the D-layer. Thus, coupling processes from the magnetosphere and to the neutral atmosphere can be considered. An additional dimension is through comparisons of the response of the two polar ionospheres to similar (or the same) geomagnetic activity. With more instruments available at the South Pole inter-hemispheric, studies have become easier to accomplish such that a fuller picture of the global response to Sun–Earth coupling can be painted.This paper presents a review of the current state of knowledge in ionospheric probing. It cannot provide a comprehensive guide of the work to date due to the scale of the topic. Rather it is intended to give an overview of the techniques and recent results from some of the instruments and facilities that are a part of the IPY cluster 63—Heliosphere Impact on Geospace. In this way it is hoped that the reader will gain a flavor of the recent research performed in this area and the potential for continuing collaboration and capabilities during the IPY (2007–2009).  相似文献   

Interhemispheric comparison of mesospheric ice layers from the LIMA model     

F.-J. Lübken  U. Berger 《Journal of Atmospheric and Solar》2007,69(17-18):2292

The new LIMA/ice model is used to study interhemispheric temperature differences at the summer upper mesosphere and their impact on the morphology of ice particle related phenomena such as noctilucent clouds (NLC), polar mesosphere clouds (PMC), and polar mesosphere summer echoes (PMSE). LIMA/ice nicely reproduces the mean characteristics of observed ice layers, for example their variation with season, altitude, and latitude. The southern hemisphere (SH) is slightly warmer compared to the NH but the difference is less than 3 K at NLC/PMC/PMSE altitudes and poleward of 70N/S. This is consistent with in situ temperature measurements by falling spheres performed at 69N and 68S. Earth's eccentricity leads to a SH mesosphere being warmer compared to the NH by up to approximately 85 km and fairly independent of latitude. In general, NH/SH temperature differences in LIMA increase with decreasing latitude and reach at 50. The latitudinal variation of NH/SH temperature differences is presumably caused by dynamical forcing and explains why PMSE are basically absent at midlatitudes in the SH whereas they are still rather common at similar colatitudes in the NH. The occurrence frequency and brightness of NLC and PMC are larger in the NH but the differences decrease with increasing latitude. Summer conditions in the SH terminate earlier compared to NH, leading to an earlier weakening and end of the ice layer season. The NLC altitude in the SH is slightly higher by 0.6–1 km, whereas the NLC altitudes itself depend on season in both hemispheres. Compared to other models LIMA/ice shows smaller interhemispheric temperature differences but still generates the observed NH/SH differences in ice layer characteristics. This emphasizes the importance of temperature controlling the existence and morphology of ice particles. Interhemispheric differences in NLC/PMC/PMSE characteristics deduced from LIMA/ice basically agree with observations from lidars, satellites, and radars.  相似文献   

太平洋副热带高压及南亚高压在NCEP/NCAR和ECMWF再分析资料中的对比研究   总被引：3，自引：0，他引：3  

陈雯  智协飞 《热带气象学报》2008,24(2):189-194

利用NCEP/NCAR和ECMWF 1961～2000年北半球逐月平均的500 hPa和100 hPa高度场再分析资料对影响我国天气、气候的重要系统--北半球西太平洋副热带高压以及南亚高压做了对比研究,发现两者在不同的再分析资料中虽然具有一定的相似性,但也存在着明显的区别.在1980年以前两者存在较大差异.NCEP/NCAR再分析资料分析出的副高明显偏弱,而其所反映的副高的变化在幅度和强度上均大于ECMWF再分析资料的结果.进一步分析发现,NCEP/NCAR再分析资料所得出的副高的年代际变化可能是不真实的.在1969年、1979～1991年间,NCEP/NCAR再分析资料中的南亚高压中心强度明显比ECMWF的强,特别是1992～1995年间,NCEP/NCAR再分析资料中的南亚高压中心强度更强且中心范围更大.此外,NCEP/NCAR再分析资料所反映的南亚高压的变化在幅度和强度上也都大于ECMWF再分析资料的结果.  相似文献   

南北涛动与南极涛动及北极涛动的相互作用   总被引：1，自引：0，他引：1  

丛菁  卢楚翰  管兆勇 《南京气象学院学报》2011,34(6):748-755

利用NCEP/NCAR再分析资料,分析了南北涛动（Interhemispheric Oscillation,IHO）与北极涛动（Arctic Oscillation,AO）和南极涛动（Antarctic Oscillation,AAO）的联系。分析表明：1）北极涛动（AO）、南极涛动（AAO）与全年各自半球中高纬度地表气压变化密切联系。其中,AO冬季强度最强,且在春季、冬季的影响范围大。而AAO对南半球中高纬的地表气压变动影响更为明显,其在夏季影响范围最大。2）南极涛动（AAO）与南北涛动（IHO）有很好的同期相关性,南极涛动可部分解释南北涛动的形成。IHO与AO存在不显著的负相关,南北半球中高纬大气运动具有相对独立性。3）南北涛动（IHO）与全球较大范围内的地面气压变化有关,而去除AAO信号后,夏季在南极地区原显著相关区显著减少,夏季AAO与IHO存在密切联系。4）南北涛动（IHO）主要与春季、秋季和冬季亚洲、欧洲北部地面气温关系密切。秋季最强,春季次之,冬季最弱。夏季IHO与全球地面气温没有较好的联系。亚欧大陆北部的热力作用可能部分地解释了南北涛动的形成。  相似文献   

Inter-Regional Comparisons on the Quaternary Large Mammalian Faunas between China and Sub-Saharan Africa     

TONG Haowen  HU Nan  LIU Jinyi  Ronald CLARKE 《《地质学报》英文版》2011,85(1):91-106

The current and dominant theory about the origin of modern humans is the out-of-Africa hypothesis, which asserts that populations of Homo sapiens left Africa 100,000 years ago and replaced indigenous populations of humans in Eurasia. Many scholars equated the out-of-Africa dispersal of humans with paleoenvironmental changes. However, until now, few have paid special attention to the faunal data and whether or not faunal patterns are supportive of the popular theory. Recent comparative study of the Chinese fauna shows that the communication of faunas between Africa and East Asia could have occurred during the Neogene, but it was very limited during the Pleistocene. In the Chinese Quaternary fauna, only 16% of the genera are also present in the sub-Saharan African fauna. There is also no element among the dominant taxa of the Chinese Quaternary fauna which can be related to the African fauna. There is no reliable proof for the existence of Hippopotamus and Giraffa, as well as Panthera leo, during the Quaternary in China. Two controversial taxa are Acinonyx and Crocuta, about which there is still argument concerning their species identification in Eurasia. It is possible that both of the genera have co-specific taxa in Africa and Eurasia. Although the two genera are confined to Africa today, they did have a long evolutionary history in China. For the Out of Africa hypothesis for Homo sapiens, the implications of the limited faunal interchanges between China and Africa are not completely clear yet.  相似文献   

Comparisons: colonial or cosmopolitan?     

Jennifer Robinson 《Singapore journal of tropical geography》2011,32(2):125-140

Editors' Note: The following is the ninth in the Singapore Journal of Tropical Geography Lecture Series. It is based on the plenary presentation of 3 September at the Annual Conference of the Royal Geography Society (with the Institute of British Geographers) held in London in 2010. In the search for a more international approach to theorizing cities, comparative methods hold considerable promise, although one concern might be that in their theoretical ambitions they foster a universalising approach rather than one appreciative of diverse and sometimes divergent urban experiences. The potentially universalizing ambitions of comparative methods lead some postcolonial theorists to question the extent to which comparativism carries the marks of colonial histories. Critics argue that some aspects of formal comparative methods can be traced to ambitious and geographically encompassing intellectual projects from the colonial era, when the interest and capacity to bring different parts of the world together within the same intellectual frame advanced significantly. This paper explores the complexities of these colonial lineages of comparative research with a view to assessing their implications for postcolonial comparative urbanism. It concludes by assessing the potential for more modest comparative experiments in a postcolonial vein through attending to the diverse vernacular cosmopolitanisms of cities. Following the spatialities of cities themselves has the potential to offer non‐universalizing but variously internationalizing theoretical engagements with different places.  相似文献