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61.
This article deals with the morpho- and lithodynamic role of ice in shaping the Arctic coasts. Taking the Pechora Sea as an example, the direct and indirect impact of ice on the sea floor and shores is described. Active gouging by ice floes, ice-rafting of sedimentary material, formation of strudel scour depressions and frozen rocks on shallows are all direct impacts. The indirect impact of ice that arrests the coastal zone for most of the year is a considerable reduction of the overall energy of waves and currents. Based on the performed analysis, we plot a schematic zonation of the Pechora Sea according to the probable impact of ice on the shores and seafloor. 相似文献
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The results obtained with the use of a lowered acoustic Doppler current profiler (LADCP) are presented. The use of the LADCP from a vessel was the first in the history of the study of the Black Sea. The measurements were carried out in the northeastern Black Sea under the auspices of the Black Sea Ecosystem Recovery Program (BSERP) in May 2004. The effect of the computation parameters on the quality and accuracy of the calculations of velocity profiles was studied. It was shown that the use of optimal parameters and reliable navigation data and setting the instrument as close to the bottom as possible could essentially enhance the accuracy of the measurements. The current velocity calculations from the LADCP data were compared with the data on the vessel drift under calm weather. The accuracy of the calculations reached 6–8 cm/s. Recommendations on the choice of the optimal parameters for processing the data on the current velocity are presented. 相似文献
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Claire Workman Love Dalen Sergey Vartanyan Beth Shapiro Pavel Kosintsev Andrei Sher Anders Gotherstrom Ian Barnes 《Quaternary Science Reviews》2011,30(17-18):2304-2308
Patterns in the spatial or temporal distribution of genotypes may be indicative of natural selection. Previous work on the woolly mammoth melanocortin-1 receptor (Mc1r) gene identified three polymorphic positions that suggest Pleistocene populations may have harboured both light- and dark-haired mammoths (Rompler et al., 2006, 313: 62). Here, we extend this work and present the first population-level analysis of a functional gene in an extinct species. We genotyped the Mc1r gene in 47 woolly mammoth samples excavated from sites across the central portion of the woolly mammoths’ former range to examine the extent of variation of this polymorphism through time and across space. Only one individual was found to be heterozygous, indicating that the frequency of the ‘light’ mutant allele was very low. We conclude that light-coloured woolly mammoths would have been very rare, and may even have been non-existent if the ‘light’ mutant allele was strongly selected against in its homozygotic form. With the increasing availability of large-scale sequencing technologies, population-level datasets capable of identifying local adaptation will become increasingly attainable. 相似文献
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M. Xue K. K. Droegemeier V. Wong A. Shapiro K. Brewster F. Carr D. Weber Y. Liu D. Wang 《Meteorology and Atmospheric Physics》2001,76(3-4):143-165
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The Palaeocene–Eocene sequence on the Komandorsky Islands is represented by sediments and minor volcanics with a total thickness of more than 3000 m. Sandstone, siltstone, mudstone, siliceous rocks and conglomerate, which have accumulated in the upper and middle parts of a deep-water fan, prevail. All the debris was delivered from the north-east, from the side of the contemporary Komandorsky basin in the Bering Sea. Products of volcanic denudation and fresh tephra dominate its composition. However, at some levels the sandstone contains fragments of jasper, quartzite, slate, schist, gabbro and granite as well as non-volcanic quartz along with a volcanic component. The heavy minerals fraction of the sandstone contains considerable quantities of apatite, zircon, garnet and chromite, as well as pyroxenes, amphiboles and magnetite. The chemical composition of the garnet is specific to metamorphic rocks. A significant admixture of chromite is indicative of denudation from an ophiolite complex. The folded and partly metamorphosed pre-Palaeogenic rocks were a source of these fragments. Their most likely source terrane was the Shirshov-Bowers chain (Cretaceous palaeoarc). The Komandorsky block originally was the forearc part of the Aleutian arc where the latter was superimposed on the Shirshov-Bauers chain. A subsequent north-west displacement of forearc structures, in response to the transform fault at the boundary between the Pacific and North American plates, could have resulted in the separation of the Komandorsky block from its Early Palaeogene debris source area. 相似文献
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