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LIUZhifei TUOShouting ZHAOQuanhong CHENGXinrong HUANGWei 《科学通报(英文版)》2004,49(20):2190-2197
The most prominent cooling event of the Earth surface during Cenozoic in the long-term transition from a non-glaciated planet, or “green-house world”, to a polar, glaciated planet, or “ice-house world”, is the Earliest Oligocene Glacial Maximum (EOGM) above the Eocene/Oligocene boundary at about 33.7 Ma. Planktonic and benthic foraminiferal oxygen and carbon isotopes, carbonate content, and coarse fraction, along with high-resolution color reflectance and magnetic susceptibility records during 35-30 Ma, from deep-water Sites 1262 and 1265, Ocean Drilling Program (ODP) Leg 208 in South Atlantic, reveal the global cooling event occurring in both surface and deep oceans. The results show that the earliest Oligocene δ^18O values during 33.5-33.1 Ma represent the magnitude of continental ice sheets on east Antarctica and indicate the large decrease in both surface and deep water temperatures of worldwideoceans. The δ^13C records show the large excursion during the period of EOGM event and indicate some types of shift in global carbon reservoir, probably demonstrating the sudden increase in organic carbon burial rates and the changes in the distribution and timing of production. At the same time, lithologic composition, carbonate content, color reflectance, and coarse fraction brought about significant changes close to the Eocene/Oligocene boundary, reflecting the abrupt deepening in the carbonate compensation depth (CCD). Changes in carbonate content were revealed from the color reflectance identify periodicities associated with eccentricity of the Earth‘s orbit (100 and 400 ka), further indicating orbitally forced global climate variations in the Early Oligocene. 相似文献
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加拿大西北部的育空地区(Yukon)分布着大面积的永久;东土层,其中埋藏的冰河时代动物的骨骼是研究古代生物DNA的重要材料。距今3万年前,地球正处末次冰期.育空地区气候变动频繁, 相似文献
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山西宁武冰洞成因分析 总被引:1,自引:0,他引:1
从冰洞所处位置分析该地区在地质时期曾经是岩溶发育区,并且经历了温暖潮湿的气候作用,逐渐形成石灰岩溶洞;而且该地区曾经是山岳冰川发育区,在第四纪冰期及间冰期时,大量的积雪、冰川融水甚至破碎冰块堆积于洞中,经过复杂的物理变化,融化和重新凝结,再加上大气降水的不断渗入,在溶洞内形成各种形态冰物质的广泛分布现象———冰洞形成;以后的年代,由于当地比较特殊的地形、气候等自然地理环境因素,冰洞得以有效保存。宁武冰洞的形成是由岩溶作用和冰川作用以及环境因素共同作用的结果。 相似文献
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RAO ZhiGuo ZHU ZhaoYu ZHANG JiaWu 《科学通报(英文版)》2007,52(2):259-266
Paleoecological records of soil δ^13Corg from three regions in the middle latitudes of the Northern Hemisphere, including the Chinese Loess Plateau (CLP), the Great Plains and adjacent areas of North America and northwestern Europe, showed different variations since the Last Glacial period. An attempt was made to evaluate the causes for the difference in δ^13Corg on the basis of the modern climatic data collected in these regions and of the modern C3 and C4 plant distributions. The analysis indicates that temperature, especially the growing season temperature, has a dominant control on the growth of C4 plants. When the mean annual or growing season temperatures are below the "threshold value", the growth of C4 plants is limited. When the temperature is above the "threshold value", C4 plants can grow under a wide range of precipitation. However, when the precipitation is high enough to favor the growth of trees, the proportions of C4 plants in local biomass will decline. The implicit control factor recovered by sedimentary records is consistent with the control factor on modern C3/C4 distribution. Pure C3 plants have been dominating the local biomass since the Last Glacial period in European loess region, mainly owing to the low local temperature. The increases in C4 plants from the late Pleistocene to the Holocene in the Chinese Loess Plateau, the Great Plains and adjacent areas, mainly reflect the influence of increasing temperature. 相似文献
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Simulation of the climatic effects of natural forcings during the pre-industrial era 总被引:2,自引:1,他引:2
YIN ChongHua YAN XiaoDong SHI ZhengGuo WANG ZhaoMin 《科学通报(英文版)》2007,52(11):1545-1558
The MPM-2,an Earth system model of intermediate complexity,is employed to study the climate sys-tem response to natural forcings during the pre-industrial era (1000-1800 AD),with a special focus on the surface air temperature (SAT) evolution. Solar radiation and volcanism are the primary natural forcings during this period. In the MPM-2,the solar radiation forcing determines the long-term trend of the climate system change,and the volcanic forcing intensifies (weakens) this trend. Ultimately,the combination of solar and volcanic forcings dominates the long-term changes of the climate system. These results are in good agreement with other model data or temperature reconstructions. Natural forcings can well explain the Little Ice Age (LIA) and the Medieval Warm Period (MWP). At the large regional scale,the SAT response to natural forcings is almost coincident with that of the Northern Hemisphere. Based on MPM-2 model results,it is concluded that the global climate gradually became cold during the pre-industrial era. However,MPM-2 model results substantially correlate with recon-structed solar and volcanic forcings. Namely,to some great extent,these results strongly rely on the forcing series data we choose. Therefore,in order to accurately simulate the secular variation of the historical climate,it is very important to reconstruct well the solar radiation change and volcanic forc-ing data are well reconstructed for the past 10000 years,at least for the past 2000 years,in addition to the model improvements. The sensitivity study on the abrupt solar radiation change indicates that the increased solar radiation not only strengthens the nonlinear response of SAT,but intensifies the global hydrological cycle. At the same time,the biosphere is also affected obviously. 相似文献
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