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261.
262.
???????й???????????????????????????Ч???????????????????????????????????????????′?????????????Ч??????????????????????????????????????ξ????????????????????????????????????????ε??????????????????????????????ò?????????????????????????????????????????????????????Ч?????????????????ε???????????????? 相似文献
263.
Implications of diverse sedimentation patterns in Hala Lake, Qinghai Province, China for reconstructing Late Quaternary climate 总被引:2,自引:0,他引:2
Bernd Wünnemann Johannes Wagner Yongzhan Zhang Dada Yan Rong Wang Yan Shen Xiaoyu Fang Jiawu Zhang 《Journal of Paleolimnology》2012,48(4):725-749
Hala Lake is located in the Qilian Mountains, Qinghai Province, China, at 4,078?m a.s.l. Its sediments contain an archive of climate and hydrologic changes during the Late Quaternary, as it is located close to the area influenced by the East-Asian summer monsoon and westerly-driven air masses. Sedimentation patterns and depositional conditions within the lake were investigated using eight sediment cores from different water depths, and this information was used to evaluate the feasibility of using a single core to reconstruct past climate and hydrological conditions. Long core H7, from the center of the lake (65?m water depth) and core H8 from a western, near-shore location (20?m water depth), were compared in detail using sediment composition and geochemical data (X-ray fluorescence, loss-on-ignition and CNS analysis). Age models were constructed using 17 AMS radiocarbon dates and indicate negligible reservoir error for sediments from the lake center and?~1,000?year errors for the near-shore sediment core. Cores H1?CH5 and HHLS21-1 revealed a sediment succession from sand and silty clay to laminated clay on the southern side of the lake. Undisturbed, finely laminated sediments were found at water depths???15?m. Core H5 (2.5?m long), from 31?m water depth, yielded abundant green algal mats mixed with clayey lake deposits and was difficult to interpret. Algae occurred between 25 and 32?m water depth and influenced the dissolved oxygen content of the stratified lake. Comparison of cores H7 and H8 yielded prominent mismatches for different time periods, which may, in part, be attributed to internal lacustrine processes, independent of climate influence. We thus conclude that data from a single sediment core may lead to different climate inferences. Common shifts among proxy data, however, showed that major climate shifts, of regional to global significance, can be tracked and allow reconstruction of lake level changes over the last 24,000?years. Results indicate advance of glaciers into the lake basin during the LGM, at which time the lake experienced lowest levels, 25?C50?m below present stage. Stepwise refilling began at ca. 16 kyr BP and reached the ?25?m level during the B?lling/Aller?d warm phase, ca. 13.5 kyr BP. A desiccation episode falls within the Younger Dryas, followed by a substantial lake level rise during the first millennium of the Holocene, a result of climate warming, which promoted glacier melt. By ca. 7.6 kyr BP, the lake reached a stable high stand similar to the present level, which persisted until ca. 6 kyr BP. Disturbed sediments in core H7 indicate a single mass flow that was most likely triggered by a major seismic event?~8.5 kyr BP. Subsequent lake development remains unclear as a consequence of data mismatches, but may indicate a general trend to deteriorating conditions and lake level lowstands at ca. 5.0?C4.2, 2.0 and 0.5 kyr BP. 相似文献
264.
博斯腾湖流域气候及湖陆风 总被引:8,自引:0,他引:8
通过流域多个气象站的资料,分析了流域气候条件,并通过对湖区测点的气象观测资料与陆区测点- 焉耆站的同步资料对比分析,讨论了博斯腾湖区域小气候其湖陆风特征。 相似文献
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268.
L1估计的分布及统计性质 总被引:3,自引:0,他引:3
推导了L1估计的密度函数,讨论了L1估计的统计性质,证明L1估计是无偏估计,同时还证明L1估计优于LS估计。 相似文献
269.
小波分析若干应用模型及在测绘中的应用和展望* 总被引:1,自引:0,他引:1
小波分析是80年代中期发展起来的应用数学理论,在众多学科领域取得了广泛的应用。文中首先对小波分析的发展作了简要概述,然后介绍了小波分析在测绘中的应用,对小波分析若干与测绘相关的应用模型进行了分析和讨论,并对小波分析在测绘中的应用前景作了展望。 相似文献
270.
王仲锋 《测绘与空间地理信息》1998,(2)
本文结合参数平差和主成分估计理论,导出了误差方程中含多重共线性时未知参数的求解公式,并以定理的形式,证明了主成分估计的解是极小范数解。由此,将主成分估计推广到秩亏网平差中,同时导出了未知参数估值之协因数阵的计算公式,同时,证明了自由网平差的传统特性。 相似文献