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341.
亚洲末次冰期冰川发育特征的深人研究表明,末次冰期冰川规模早期大于晚期。最近,国内外已经注意到末次冰期中期(MIS3b)存在全球性质的降温时段,此时湿度大,并与低温相结合,引起冰川前进的规模也大于干冷的末次冰盛期(LGM),指示末次冰期以来的冰川演化不仅仅是亚洲自身的区域性特点,而且有可能带有全球性.同时,东亚沿海山地冰川发育表现为与大陆内部不一致的特征,说明即使在同一季风系统条件下,由于地理位置、水热条件的不同,也可以引起冰川演化的区域分异,呼应早期提出的冰川发育“异时性”理论。从研究末次冰期冰川发育规模入手,讨论西风带与季风带对冰川发育规模的影响,结合其它地区末次冰期冰川发育特点,进而得出:由于海-地-汽系统循环在不同区域、不同时期对冰川发育影响不同,在各地冰川最大前进规模和时间是一致或不一致的,在10ka和30ka时间尺度上冰川发育可能存在“同时”和“异时”两种情况。 相似文献
342.
1 IntroductionIthas been accepted thatthe glacialextentin the early stage w as largerthan thatin the late stagein Eastern A sia during the Last G laciation and w as different from Europe and N orth A m erica(Li, 1992; Cui et al., 2000). M any scholars hav… 相似文献
343.
LATE‐GLACIAL GLACIER EVENTS IN SOUTHERNMOST SOUTH AMERICA: A BLEND OF ‘NORTHERN’ AND 'SOUTHERN’ HEMISPHERIC CLIMATIC SIGNALS? 总被引:2,自引:0,他引:2
D.E. SUGDEN M.J. BENTLEY C.J. FOGWILL N.R.J. HULTON R.D. McCULLOCH R.S. PURVES 《Geografiska Annaler: Series A, Physical Geography》2005,87(2):273-288
ABSTRACT. This paper examines new geomorphological, chronological and modelling data on glacier fluctuations in southernmost South America in latitudes 46–55°S during the last glacial–interglacial transition. Establishing leads and lags between the northern and southern hemispheres and between southern mid‐latitudes and Antarctica is key to an appreciation of the mechanisms and resilience of global climate. This is particularly important in the southern hemisphere where there is a paucity of empirical data. The overall structure of the last glacial cycle in Patagonia has a northern hemisphere signal. Glaciers reached or approached their Last Glacial Maxima on two or more occasions at 25–23 ka (calendar) and there was a third less extensive advance at 17.5 ka. Deglaciation occurred in two steps at 17.5 ka and at 11.4 ka. This structure is the same as that recognized in the northern hemisphere and taking place in spite of glacier advances occurring at a time of high southern hemisphere summer insolation and deglaciation at a time of decreasing summer insolation. The implication is that at orbital time scales the‘northern’ signal dominates any southern hemisphere signal. During deglaciation, at a millennial scale, the glacier fluctuations mirror an antiphase 'southern’ climatic signal as revealed in Antarctic ice cores. There is a glacier advance coincident with the Antarctic Cold Reversal at 15.3–12.2 ka. Furthermore, deglaciation begins in the middle of the Younger Dryas. The implication is that, during the last glacial–interglacial transition, southernmost South America was under the influence of sea surface temperatures, sea ice and southern westerlies responding to conditions in the 'southern’ Antarctic domain. Such asynchrony may reflect a situation whereby, during deglaciation, the world is more sensitized to fluctuations in the oceanic thermohaline circulation, perhaps related to the bipolar seesaw, than at orbital timescales. 相似文献
344.
Pollen and dinoflagellate cyst assemblages from Core SU 81-18 recovered off Portugal (37°46′N, 10°11′W; 3135-m water depth) have been used to document the short-term environmental changes that occurred in southwest Europe since 25,000 yr B.P. The relationship between the oceanic and continental environments has been further examined by the use of other marine proxies (coarse sedimentary fraction, foraminifera) and by comparison with proximal land pollen records. Heinrich 2 (H2) and Heinrich 1 (H1) events were the most extreme parts of the highly variable last glacial period, with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site. Our study shows that H1 and H2 are divided in two distinct phases: one with Neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris, reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site; the other with dinoflagellate cysts of subpolar affinity, Bitectatodinium tepikiense, reflecting a seasonal control marked by warm summer SST and cold winter SST. 相似文献
345.
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347.
青藏高原西北部17000年以来的介形类及环境演变 总被引:32,自引:3,他引:32
通过班公错和松西错两钻孔以及红山湖地层剖面的介形类分析,讨论了昆仑山、喀喇昆仑山地区晚更新世晚期以来的主要气候事件和环境变迁。 相似文献
348.
Using a regional climate model MM5 nested to an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate the relative Last Glacial Maximum (LGM) climate response to different mechanisms over China. Model simulations of the present day (PD) climate and the LGM climate change are in good agreement with the observation data and geological records, especially in the simulation of precipitation change. Under the PD and LGM climate,changes of earth orbital parameters have a small influence on the annual mean temperature over China.However, the magnitude of the effect shows a seasonal pattern, with a significant response in winter. Thus,this influence cannot be neglected. During the LGM, CO2 concentration reached its lowest point to 200 ppmv. This results in a temperature decrease over China. The influences of CO2 concentration on climate show seasonal and regional patterns as well, with a signi cant influence in winter. On the contrary, CO2 concentration has less impact in summer season. In some cases, temperature even increases with decreasing in CO2 concentration. This temperature increase is the outcome of decrease in cloud amount; hence increase the solar radiation that reached the earth's surface. This result suggests that cloud amount plays a very important role in climate change and could direct the response patterns of some climate variables such as temperature during certain periods and over certain regions. In the Tibetan Plateau, the temperature responses to changes of the above two factors are generally weaker than those in other regions because the cloud amount in this area is generally more than in the other areas. Relative to the current climate, changes in orbital parameters have less impact on the LGM climate than changes in CO2 concentration. However,both factors have rather less contributions to the climate change in the LGM. About 3%-10% changes in the annual mean temperature are contributed by CO2. 相似文献
349.
Late Quaternary vegetation history and environmental changes in a biodiverse tropical ecosystem are inferred from pollen, charcoal and carbon isotope evidence derived from a ∼ 48,000-yr sedimentary record from the Uluguru Mountains, a component of the Eastern Arc Mountains of Kenya and Tanzania. Results indicate that Eastern Arc forest composition has remained relatively stable during the past ∼ 48,000 yr. Long-term environmental stability of the Eastern Arc forests has been proposed as a mechanism for the accumulation and persistence of species during glacial periods, thus resulting in the diverse forests observed today. The pollen and isotope data presented here indicate some marked changes in abundance but no significant loss in moist forest taxa through the last glacial maximum, thereby providing support for the long-term environmental stability of the Eastern Arc. Anthropogenic activities, including burning and forest clearance, were found to play a moderate role in shaping the mosaic of forest patches and high-altitude grasslands that characterise the site today; however, this influence was tempered by the inaccessibility of the mountain. 相似文献
350.
末次盛冰期以来南海南部海平面及海洋底水温度均发生了很大的变化. 为了研究南海南部天然气水合物稳定带厚度在这个过程中的变化情况及其对环境的影响,我们利用相关的计算公式,并编制了计算稳定带厚度的程序,在南海南部的南沙海槽、曾母盆地、巴拉望盆地和苏禄海等四个重点海域选取了35个点进行末次盛冰期及目前稳定带厚度的计算. 计算结果表明,南海南部末次盛冰期和目前的天然气水合物稳定带厚度分别为262m和233m;甲烷资源量分别为269×1013m3和239×1013m3;水合物资源量分别为164×1011m3和146×1011m3. 这说明自末次盛冰期以来,南海南部稳定带厚度平均减薄了29m,平均减薄百分比为12%,同时释放了大约30×1012m3的甲烷,这些甲烷对环境产生了较大影响,对末次冰期的结束起了较大作用. 相似文献