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1.
敦德冰岩芯古气候环境记录的初步研究 总被引：9，自引：0，他引：9
中美合作首次研究了中国西部祁连山敦德冰帽的冰岩芯。研究说明该冰帽的冰岩芯对研究古气候及环境变化具有很好的代表性,能够反映中国西部乃至北半球的气候、环境变化的过程和量级。δ18O、冰晶尺寸的高值及微粒含量的低值与高温期对应,δ18O、冰晶尺寸的低值及微粒含量的高值与低温期相对应。冰岩芯上部所记录的本世纪以来的气候变化与其它气候记录所反映的情况一致。冰岩芯的下部（125m以下）反映了最后一次冰期的气候及环境。根据冰晶粒径增长速度计算,该冰川从末次冰期到全新世高温期的气温差值是7℃。 相似文献
2.
长江三角洲千年冬温序列与古里雅冰芯比较 总被引：9，自引：5，他引：4
利用长江三角洲史料优势,重建公元820年代以来,年代级冬温序列.为测试古里雅冰芯记录的影响力,与之作比较研究.结果显示:其年代级变化背景有很好的对应关系,年代级变化有大同小异的复杂情况.舍弃量级,就年代级温度,降水升降,约有一半是同步的,且有大致对应的温湿组合.说明两地虽远隔数千公里,环境生态条件悬殊,年代级气候变化仍有响应.最后就形成响应的成因机制作初步分析。 相似文献
3.
Greenland Ice Sheet is one of the two largest ice sheets on the planet. Under the background of climate warming, the melting of the Greenland ice sheet and its contribution to sea level rise has become an international hot issue. The whole melting of the Greenland ice sheet can cause the global sea level to rise by about 7.3 meters. However, the dynamic mechanism that affects the mass balance of ice sheet is still unclear and is the greatest uncertainty source for predicting the rise in sea level in the future. The National Key Research and Development Program of China “A Study of the Monitoring, Simulation and Climate Impact of Greenland Ice Sheet” conducts monitoring and simulation studies on the key processes of instability of the “ice sheet-outlet glacier-sea ice” system, and establishes a satellite-airborne-ground integrated observation system, supporting the numerical simulation and impact research of the ice sheet and its surrounding sea ice, laying the foundation for long-term monitoring and international cooperation in Greenland. This program will work to reduce the uncertainty of sea level change projections by improving the ice sheet dynamic model forced by the ice core records, reveal the driving mechanism of sea ice changes around the ice sheet, focusing on the Northwest Passage, evaluate and forecast the navigation window period. The results of the project will deepen the understanding of the changes and impacts of the Arctic cryosphere, serve the safe navigation and operation of the Northwest Passage, and provide scientific support for the comprehensive risk prevention of coastal zones in China. 相似文献
4.
冰心包含大量的古气候资料和古生物学信息,这些信息对于从远古到现代的气候变化和生物进化都很重要。如何高效快速地获取无污染的冰心是极地科学家的一个重要课题。冰层空气反循环钻具采用双壁钻杆形成反循环通道,内管提供了从钻头底部到表面的冰屑和冰心的连续通道。钻具通过卡断机构卡断冰心,通过反循环通道不断运移冰心,从而实现连续钻具连续取心。本文采用ABAQUS软件对冰心卡断过程进行分析,运用XFEM断裂准则以及Explicit显式方法求解,选出适宜的卡断器尺寸和中心通道尺寸,从而得到更好的反循环钻进效果。 相似文献
5.
Jerzy Nawrocki Andrij B. Bogucki Petro Gozhik Maria &#x;anczont Magdalena Pa&#x;czyk Karol Standzikowski Maryna Komar Olga Rosowiecka Olena Tomeniuk 《Boreas: An International Journal of Quaternary Research》2019,48(4):940-952
The azimuth of imbrication of minimum magnetic susceptibility axes in the youngest loess from Ukraine defines prevailing wind directions during aeolian sedimentation. It changes along the studied sections. These changes can be directly correlated with the fluctuations of the Fennoscandian Ice Sheet. The northern and northeastern winds noted in the loess succession separated by a period when southwestern to southeastern winds were predominant may be correlated with two main phases of ice‐sheet advance during the Last Glacial Maximum. The ice‐sheet advances towards the areas of loess deposition generated katabatic winds that influenced aeolian sedimentation in the periglacial zone. A period of relatively stable wind directions during a younger phase of the Last Glacial Maximum was interrupted by periods with more chaotic wind regime most probably caused by fluctuations of the Fennoscandian Ice Sheet during its retreat from the peri‐Baltic part of Europe. These intervals occur where initial soils developed. The distribution of anisotropy of magnetic susceptibility axes defined along the periglacial loess sections from central and eastern Europe can serve to constrain fluctuations of the Fennoscandian Ice Sheet. 相似文献
6.
Studies in southern British Columbia have shown that Cordilleran Ice Sheet flow was controlled by topograph, even in full glacial time. New ice‐flow evidence from the Nass River region, northern British Columbia, however, indicates that ice was thicker there and that the continental ice‐sheet phase of glaciation was reached. Inspection of high elevation sites has revealed a suite of ice‐flow indicators (mainly striae) undetected by earlier work. These suggest that at the Last Glacial Maximum (Fraser Glaciation), ice flowed southwestward across the Nass River region from an ice divide that probably was located in the Skeena Mountain area. Comparisons with adjacent work allow this divide to be mapped over a wide area. The results suggest that maximum ice thicknesses in the northern part of the Cordilleran Ice Sheet were larger than reported previously. The location of storm tracks in full glacial time may have played an important role in the production of an ice sheet that was thicker in northern British Columbia than it was in the southern half of the province. During deglaciation, ice thinned and gradually became confined to fiords and valleys, resulting in numerous and variable ice‐flow directions at that time. Topographic control was thus exerted on ice flow only after the glacial maximum was reached, despite the significant amount of relief in this region. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
7.
青藏高原现代最大冰原区第四纪冰川作用 总被引：2，自引：1，他引：1
普若岗日冰原是青藏高原最大的冰原,总面积达400km2.野外观察表明,从现代冰舌前端开始向山外有5套终碛垄和侧碛垄系列,分别称之为冰碛垄Ⅰ、Ⅱ、Ⅲ、Ⅳ和Ⅴ.根据地貌位置、地层关系、相对风化程度、风的改造程度和覆盖在有冰川漂砾的戈壁上的沙子的电子自旋共振(ESR)年代,并与中国西部山地第四纪冰川数值年代比较,这些冰碛垄分别形成于现代冰川、小冰期、新冰期、末次冰期晚阶段和早阶段.冰碛垄V中的花岗岩漂砾散布于距山前6km以内的山麓平原,说明在第四纪晚期冰原西坡的古冰川虽到达山麓平原,但未能与邻近山地古冰川相连形成统一大冰盖. 相似文献
8.
High‐resolution swath bathymetry and TOPAS sub‐bottom profiler acoustic data from the inner and middle continental shelf of north‐east Greenland record the presence of streamlined mega‐scale glacial lineations and other subglacial landforms that are formed in the surface of a continuous soft sediment layer. The best‐developed lineations are found in Westwind Trough, a bathymetric trough connecting Nioghalvfjerdsfjorden Gletscher and Zachariae Isstrøm to the continental shelf edge. The geomorphological and stratigraphical data indicate that the Greenland Ice Sheet covered the inner‐middle shelf in north‐east Greenland during the most recent ice advance of the Late Weichselian glaciation. Earlier sedimentological and chronological studies indicated that the last major delivery of glacigenic sediment to the shelf and Fram Strait was prior to the Holocene during Marine Isotope Stage 2, supporting our assertion that the subglacial landforms and ice sheet expansion in north‐east Greenland occurred during the Late Weichselian. Glacimarine sediment gravity flow deposits found on the north‐east Greenland continental slope imply that the ice sheet extended beyond the middle continental shelf, and supplied subglacial sediment direct to the shelf edge with subsequent remobilisation downslope. These marine geophysical data indicate that the flow of the Late Weichselian Greenland Ice Sheet through Westwind Trough was in the form of a fast‐flowing palaeo‐ice stream, and that it provides the first direct geomorphological evidence for the former presence of ice streams on the Greenland continental shelf. The presence of streamlined subglacially derived landforms and till layers on the shallow AWI Bank and Northwind Shoal indicates that ice sheet flow was not only channelled through the cross‐shelf bathymetric troughs but also occurred across the shallow intra‐trough regions of north‐east Greenland. Collectively these data record for the first time that ice streams were an important glacio‐dynamic feature that drained interior basins of the Late Weichselian Greenland Ice Sheet across the adjacent continental margin, and that the ice sheet was far more extensive in north‐east Greenland during the Last Glacial Maximum than the previous terrestrial–glacial reconstructions showed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
Marine ice sheets are grounded on land which was below sea level before it became depressed under the ice-sheet load. They are inherently unstable and, because of bedrock topography after depression, the collapse of a marine ice sheet may be very rapid. In this paper equations are derived that can be used to make a quantitative estimate of the maximum size of a marine ice sheet and of when and how rapidly retreat would take place under prescribed conditions. Ice-sheet growth is favored by falling sea level and uplift of the seabed. In most cases the buttressing effect of a partially grounded ice shelf is a prerequisite for maximum growth out to the edge of the continental shelf. Collapse is triggered most easily by eustatic rise in sea level, but it is possible that the ice sheet may self-destruct by depressing the edge of the continental shelf so that sea depth is increased at the equilibrium grounding line.Application of the equations to a hypothetical “Ross Ice Sheet” that 18,000 yr ago may have covered the present-day Ross Ice Shelf indicates that, if the ice sheet existed, it probably extended to a line of sills parallel to the edge of the Ross Sea continental shelf. By allowing world sea level to rise from its late-Wisconsin minimum it was possible to calculate retreat rates for individual ice streams that drained the “Ross Ice Sheet.” For all the models tested, retreat began soon after sea level began to rise (～15,000 yr B.P.). The first 100 km of retreat took between 1500 and 2500 yr but then retreat rates rapidly accelerated to between 0.5 and 25 km yr?1, depending on whether an ice shelf was present or not, with corresponding ice velocities across the grounding line of 4 to 70 km yr?1. All models indicate that most of the present-day Ross Ice Shelf was free of grounded ice by about 7000 yr B.P. As the ice streams retreated floating ice shelves may have formed between promontories of slowly collapsing stagnant ice left behind by the rapidly retreating ice streams. If ice shelves did not form during retreat then the analysis indicates that most of the West Antarctic Ice Sheet would have collapsed by 9000 yr B.P. Thus, the present-day Ross Ice Shelf (and probably the Ronne Ice Shelf) serves to stabilize the West Antarctic Ice Sheet, which would collapse very rapidly if the ice shelves were removed. This provides support for the suggestion that the 6-m sea-level high during the Sangamon Interglacial was caused by collapse of the West Antarctic Ice Sheet after climatic warming had sufficiently weakened the ice shelves. Since the West Antarctic Ice Sheet still exists it seems likely that ice shelves did form during Holocene retreat. Their effect was to slow and, finally, to halt retreat. The models that best fit available data require a rather low shear stress between the ice shelf and its sides, and this implies that rapid shear in this region encouraged the formation of a band of ice with a preferred crystal fabric, as appears to be happening today in the floating portions of fast bounded glaciers.Rebound of the seabed after the ice sheet had retreated to an equilibrium position would allow the ice sheet to advance once more. This may be taking place today since analysis of data from the Ross Ice Shelf indicates that the southeast corner is probably growing thicker with time, and if this persists then large areas of ice shelf must become grounded. This would restrict drainage from West Antarctic ice streams which would tend to thicken and advance their grounding lines into the ice shelf. 相似文献
10.
唐古拉山地区第四纪冰川作用与冰川特征 总被引：4，自引：2，他引：2
自中更新世以来,唐古拉山地区发生过3次更新世冰川作用(即昆仑冰期、倒数第二次冰期和末次错冰期)和2次全新世晚期冰进(即新冰期和小冰期冰进).昆仑冰期(最大冰期)发生在中更新世早期(0.80～0.60MaBP),不仅是本区最早的一次冰期,而且也是冰川规模最大的一次冰期,当时的冰川规模比现代冰川大16～18倍;倒数第二次冰期发生在中更新世晚期(0.30～0.135MaBP),比现代冰川大13～15倍;末次冰期发生在晚更新世晚期,应分为末次冰期早冰阶(75.0～58.0kaBP)和晚冰阶(32.0～15.0kaBP,23.0kaBP时达到极盛),但在唐古拉山地区截止目前还未找到早冰阶的冰川遗迹,因此,只对末次冰期的晚冰阶(LMG)进行了探讨.LMG时,冰川规模比现代冰川大10倍;新冰期发生在全新世高温期后,冰碛物的14C测年为(3540±160)aBP,冰川规模略大于现代冰川;小冰期发生在15～1世纪,冰川规模已接近于现代冰川.由于青藏高原的上升,对高原腹部地区引起的干旱化过程和水分严重不足,使唐古拉山地区的冰川自昆仑冰期以来,冰川规模一次比一次明显的减小. 相似文献