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本文介绍了应用碳化理(Li2C2)法进行化学制样测定14C年代获得成功的试验.抑制鋰的升华作用是成功的关键.文中提出了改革鋰反应器冷却装置的根据和方案.试验结果是令人满意的.从CO2到C2H2的转化中碳的收率高达98%(而StC2法为70%左右).本文发表了40个14C年代数据,其中4个进行了互校对比,一致性很好. 相似文献
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The reliability of lichenometric dating is dependent on a good understanding of lichen growth rates. The growth rate of lichens can be determined from direct measurement of growing lichens or indirect methods by measuring lichens growing on surfaces of known age, although there are limitations to both approaches. Radiocarbon (14 C) analysis has previously been used in only a handful of studies to determine lichen growth rates of two species from a small area of North America. These studies have produced mixed results; a small amount of carbon turnover appears to occur in one of the species ( Caloplaca spp.) previously investigated introducing uncertainty in the growth rate, while much higher carbon cycling occurred in another ( Rhizocarpon geographicum ), making the 14 C approach unsuitable for estimating growth rates in the species most commonly used in lichenometric dating. We investigated the use of bomb-14 C analysis to determine the growth rate of a different crustose species ( Pertusaria pseudocorallina ) common to Northern Europe. 14 C-based growth rates were considerably higher than growth rates of morphologically similar species based on direct measurement made at locations nearby and elsewhere in the UK. This observation strongly suggests that a degree of carbon turnover probably occurs in Pertusaria pseudocorallina , and that bomb-14 C analysis alone cannot be used to determine lichen age or absolute growth rates in this lichen species. 相似文献
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Torbjörn Andesson 《Polar research》2000,19(2):271-273
This note reports the occurrence of two generations of 14C dated raised beach deposits at Pricepynten. southern Prins Karls Forland, western Svalbard, dated to < 12 Kya and >30 Kya. In addition two new 14C ages of ca. 9.2 and 1.8 Ky are presented from Myrilus eclulis and a buried peat deposit, respectively. 相似文献
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沙漠湖泊沉积物是研究气候环境变化的珍贵材料,湖泊岩芯年代学研究是重建古气候和古环境的基础和前提,然而其年代的测定存在诸多困难,尤其是年轻湖泊沉积物测年一直是当前地质年代学研究的难题。~(14)C测年作为一种传统的测年方法已被广泛应用于各类湖泊年轻沉积物的年代测定。巴丹吉林沙漠湖泊年轻沉积物能否利用~(14)C方法进行测年,其可靠性如何,需进行研究和验证。选择巴丹吉林沙漠腹地的两支岩芯(BR-1和YD-1),对其进行了~(14)C测年,并与已有的~(210)P_(buns)及其推算年代进行了对比。结果表明:1)沙漠湖泊中的植物残体来源存在较大的随机性,可能是原有的更老沉积层中的植物残体的再沉积,测年结果偏老约1000年。2)湖泊岩芯中有机沉积物样品的年代结果基本符合沉积规律,但受硬水效应的影响,其年代整体偏老400~900年。3)与~(210)P_(buns)年代对比,两种不同测年物质所测得的年代均存在不同程度的偏老现象,表明岩芯所在湖泊~(14)C年龄受多种因素影响,总体存在很大的不确定性。在测年材料极为稀缺的沙漠丘间湖区,利用岩芯中的植物残体、沉积物有机质进行~(14)C测年,可能受老沉积层中测年材料再沉积、湖水碳库效应等因素的影响,~(14)C年代存在诸多不确定性。因此,在对巴丹吉林沙漠丘间湖泊年轻沉积物测年研究过程中应谨慎运用。 相似文献
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Amazing organogenic deposits were encountered within the terminal moraine zone of Renardbreen, north-western part of Wedel Jarlsberg Land. Pollen analyses and ,14 C dating locate the deposits at the Middle Late Subatlantic transition. The position of these deposits indicates possible glacial advances 3,500-2,000 years BP and during the Little Ice Age, respectively. Remnants of human activity at least as old as the 9th century were also found within organogenic deposits. 相似文献
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Summary. The far-field displacement amplitude spectra of 14 earthquakes from Iran, Fiji Islands, Tonga—Kermadec Islands, and South America were obtained using the long-period P and 5-wave records of the WWSSN stations. Despite recent improvements in theories of the seismic-source mechanism there is continuing doubt concerning the interpretation of the observed seismic spectrum. Although the dislocation model has been adopted by many investigators, and in particular Brune's model is widely used, there has often not been satisfactory evidence in the observed spectral data to justify this. Generally speaking, however, the spectral structures obtained in the present work have a form closely similar to those calculated by Brune and Savage, and it is shown that anomalies in the observed amplitude spectral structure are most likely due to noise and propagation effects. 相似文献
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KATHY J. LICHT WENDY L. CUNNINGHAM JOHN T. ANDREWS EUGENE W. DOMACK ANNE E. JENNINGS 《Polar research》1998,17(2):203-216
To compare north and south polar marine paleoenvironments over the last 30,000 years, comparable chronological (radiocarbon) records must be developed and refined. Many areas in the polar regions do not preserve marine carbonates (foraminifera, mollusks), and thus age determinations, of necessity, are based on the acid-insoluble organic (AIO) fraction of the sediment. Although AIO ages are problematic and rarely used in the Arctic, they provide reasonable and consistent chronologies for the Ross Sea, Antarctica. AIO dates are meaningful in the Ross Sea because there are relatively high levels of productivity, good preservation of marine biogenic material in the sediment, and little input of terrigenous sediment and old/dead carbon. Event stratigraphy based upon proxy records of biogenic silica and δ13 C can be used to assess the reliability of the AIO dates and surface age corrections. Reconstructed time-series of changes in the biogenic silica content of cores from the western Ross Sea show apparent similarities with the 'classic'deglacial climate sequence of the northern North Atlantic. Once the absolute ages of the antarctic AIO dates are constrained by independently dated records to validate surface age corrections, it will be possible to directly compare the timing of events such as ice-rafting events in the sedimentary record. 相似文献
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A new high-resolution magnetostratigraphic record from the eastern Arctic Ocean has yielded further evidence for the existence of the Laschamp excursion (37–35 ka), the Mono Lake excursion (27–25.5 ka) and possibly another very short excursion (22 ka) inferred from steep negative inclinations. Ages are based on nine AMS (accelerator mass spectrometry) 14 C dates, oxygen isotope stratigraphy and correlation with ODP site 983. Estimates of relative palaeointensity variations for the time interval from 80 to 10 ka have revealed that the documented geomagnetic excursions are linked to large fluctuations of the relative palaeointensity. The lowest values were obtained for the two excursions and the normal–reversed (N–R) and reversed–normal (R–N) transitions of the Laschamp polarity excursion, which itself is characterized by a slight increase of relative palaeointensity during its reversed state. The results are in general agreement with palaeointensity studies from other regions, indicating that these fluctuations could be global phenomena and that the geomagnetic field of the Brunhes Chron was very variable in amplitude as well as in geometry. The new result is one of the rare records comprising large directional as well as large relative palaeointensity variations. 相似文献
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Norbert R. Nowaczyk Martin Antonow Jochen Knies Robert F. Spielhagen 《Geophysical Journal International》2003,155(3):1065-1080
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《寒旱区科学》2023,(6):251-252
<正>In the context of economic globalization and regional integration,the development of cold regions has global significance and international impact on the common destiny of human survival and development.Buildings,dams,highways,railways,and other infrastructure have been developed rapidly in permafrost and seasonally frozen regions in the past several decades,which prompts the need to establish an international platform to exhibit the latest technological advancements in cold regions dev... 相似文献
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《The Professional geographer》2013,65(3):309-317
In this second report from the Long Range Planning Committee, the Chairman of the Communications Task Force discusses the purpose, structure, and functioning of Specialty Groups, which are to be established in accordance with a Committee recommendation approved by the AAG Council. 相似文献