共查询到10条相似文献，搜索用时 359 毫秒
1.
东南极冰盖中山站－DOme A断面路线考察的初步结果 总被引：7，自引：11，他引：7
1996年以来，中国国家南极考察队连续3次进行了南极冰盖内陆考察，最远点距海岸1100km,海拔3900米，沿考察路线对冰盖表面地形，表面雪层特征，雪积累速率，冰体厚度和运动速度等进行现场观测，采集0．6－3．3米深度雪坑样品，在4个地点钻取50－100m，深度冰芯5支，部分资料和样品的初步分析表明，由于研究区域毗邻Lambert冰川和格罗夫山，冰面地形较多起伏，中段很大区域坡面朝向Lambert冰川，自中山站向内陆460km积累速率为46－210kg.m^-2.a^-1(相当于12－60厘米厚度雪层），表面1米深度雪的密度为350－450kg/m^-3，雪变成冰的深度（密度达830kg.m^-3)在几个冰芯钻取地点大约为60米，说明研究区域内雪的变质过程基本相同，300km处50米冰芯初步分析显示，过去几十年积累速率和温度均呈上升趋势，这虽然与南极地区其他针点的结果相一致，但却和毗邻的Lambert冰川西侧研究结果相反。 相似文献
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达索普冰川海拔7100m处气泡封闭过程研究 总被引：7，自引：6，他引：1
通过对希夏邦马峰北坡达索普冰川气泡形成过程的研究表明,随着深度增加,粒雪中开放气孔体积逐渐减小,但粒雪层仍保持良好的气体渗透性,直到粒雪一冰转变层位开放气孔完全与大气隔离,形成彼此分离的孤立气泡．显然,冰内气泡包裹气体与同层位的冰存在年龄差,只有在气孔完全封闭后,气泡封闭的深度亦不相同,但气泡封闭处对应的密度都大致相当,为079～0．83Mg·m－3．达索普冰川粒雪层中开放气孔在40～47m深度范围内快速封闭,在45m处有50％的气泡形成计算得出气泡中气体与同层位冰的年龄差为59a,同层位气泡中的气体所代表的主体年代分配范围为11a． 相似文献
3.
Jeffrey P. Severinghaus Alexi Grachev Nicolas Caillon 《Geochimica et cosmochimica acta》2003,67(3):325-343
We describe a method for measuring the 40Ar/36Ar ratio and the 84Kr/36Ar ratio in air from bubbles trapped in ice cores. These ratios can provide constraints on the past thickness of the firn layer at the ice core site and on the magnitude of past rapid temperature variations when combined with measured 15N/14N. Both variables contribute to paleoclimatic studies and ultimately to the understanding of the controls on Earth’s climate. The overall precision of the 40Ar/36Ar method (1 standard error of the mean) is 0.012‰ for a sample analyzed in duplicate, corresponding to ±0.6 m in reconstructed firn thickness. We use conventional dynamic isotope ratio mass spectrometry with minor modifications and special gas handling techniques designed to avoid fractionation. About 100 g of ice is used for a duplicate pair of analyses. An example of the technique applied to the GISP2 ice core yields an estimate of 11 ± 3K of abrupt warming at the end of the last glacial period 15,000 years ago. The krypton/argon ratio can provide a diagnostic of argon leakage out of the bubbles, which may happen (naturally) during bubble close-off or (artifactually) if samples are warmed near the freezing point during core retrieval or storage. Argon leakage may fractionate the remaining 40Ar/36Ar ratio by +0.007‰ per ‰ change in 84Kr/36Ar, introducing a possible bias in reconstructed firn thickness of about +2 m if thermal diffusion is not accounted for or +6 m if thermal diffusion effects are quantified with measured 15N/14N. Reproducibility of 84Kr/36Ar measured in air is about ±0.2‰ (1 standard error of the mean) but is about ±1‰ for ice core samples. Ice core samples are systematically enriched in 84Kr/36Ar relative to atmosphere by ∼5‰, probably reflecting preferential size-dependent exclusion of the smaller argon atom during bubble entrapment. Recent results from the Siple Dome ice core reveal two climate events during the last deglaciation, including an 18-m reduction in firn thickness associated with an abrupt warming at sometime between 18 and 22 kyr BP and a partial or total removal of the firn during an ablation event at 15.3 kyr BP. 相似文献
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马兰和普若岗日冰芯记录了气候环境变化对中低纬度地区微生物群落分布和矿物结构的影响.研究表明,可培养微生物群落组成以细菌为主.进一步的16S(18S)rDNA序列分析表明,嗜细胞菌-黄杆菌属和衣藻属是冰芯微生物的优势地方菌群.微生物群落密度与矿物含量有密切的对应关系,较多的微生物群落一般出现在矿物含量较高的冰层中.但是,在个别具有很多矿物微粒的样品中却没有出现预期很多的微生物.马兰冰芯研究还揭示了寒冷期微生物群落密度大和暖期微生物群落密度小的反相关关系.与暖期W1中发生的一次较大的降温突变相对应,在L1中微生物数量也出现一个峰值.该研究为利用冰芯记录重建古气候环境变化提供了另一个有效手段. 相似文献
6.
本描述了单轴压缩蠕变实验结果。试样包括ｃ轴取向为随机分布和非随机分布的冰、人造冰和取自南极洛多姆冰帽的冰芯冰，各向同性冰芯冰和人造的最小应变率存在差别，未获得合理的解释。方位组构与应力状态相容时，各赂异性冰的最小应变率高于各向同性冰的最小应变率，随着第三应谱阶段的发展，冰芯冰和人造冰的第三应变率趋近相同的恒定值，实验后冰芯冰和人造冰ｃ轴方位组构类型相同，晶粒尺寸也接近。 相似文献
7.
电感耦合等离子体质谱直接测定冰芯样品中痕量铅 总被引：6，自引：0，他引：6
利用电感耦合等离子体质谱仪对冰芯样品中超痕量Pb进行了直接测定。确定了测定溶液中浓度为ng/L级Pb的最佳仪器参数，载气流速、进样速度等与灵敏度之间的关系,浓度和扫描参数对分析精度的影响。仪器对Pb的质量浓度在20～100ng/L的分析精度(RSD，n=3)＜10%,标准加入回收率在85%～115%，检测下限为0.62ng/L，并给出了采自可可西里马兰冰川M3冰芯中Pb的分析结果。 相似文献
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膨胀土是一种特殊的黏土,具有明显的胀缩性和多裂隙性,在寒区渠道工程中极易诱发各种冻害。单轴压缩特性是冻土物理力学特性的重要分支,为研究冻结膨胀土的单轴压缩特性,开展了不同干密度和温度下冻结膨胀土单轴压缩试验。试验结果表明:随着干密度的增加,各温度工况下试样的应力-应变关系曲线均由弱应变软化转为应变硬化形态,且试验温度越高,曲线的软化特征越显著。不同温度工况下试样的破坏模式差异明显。当试验温度为-2℃时,试样破坏时其表面出现明显的局部坍塌与剥落,而-5℃、-10℃和-15℃工况下试样的最终破坏形态均为“鼓状”破坏,试样表面无明显的裂缝和剪切面。冻结膨胀土试样的单轴抗压强度随干密度的增加而线性增大,亦随温度的降低而增大,但在不同的温度区间内增幅不同,其变化幅度主要与试样内部含冰量密切相关。此外,试样的弹性模量随着干密度的增大和温度的降低均线性增大。 相似文献
9.
Robert L Fleischer Howard R Hart Wallace R Giard 《Geochimica et cosmochimica acta》1974,38(3):365-380
Measurements of cosmic ray track densities are presented for soil samples from Apollo 15, 16 and 17. Median track densities are used to infer total effective exposure times within ~15 cm of the lunar surface. Minimum track densities are used to derive the time of the last impact-produced rearrangement of soil grains. For samples from near various craters ages are derived of 40 m.y. for St. George, 6 (±3) m.y. for S. Ray, 25–90 m.y. for Plum, and 20–35 m.y. for Shorty. The material of 15003. the Apollo 15 deep core at depths of 120–160 cm, is inferred to have been deposited at an average rate of ≥0.35 cm/m.y. The Apollo 16 core at 41–47 cm depths. 60007, appears to be well mixed and was covered up by deposition at 0.3 cm/m.y. for the next few m.y. after its deposition. 相似文献
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This paper presents an elasto‐plastic model for unsaturated compacted soils and experimental results obtained from a series of suction‐controlled triaxial tests on unsaturated compacted clay with different initial densities. The initial density dependency of the compacted soil behaviour is modelled by establishing experimental relationships between the initial density and the corresponding yield stress and thereby between the initial density and the location and slope of normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure surface and the yield surface in the deviatoric plane are given by the extended SMP criterion. A considerable number of the isotropic compression, triaxial compression and extension tests on unsaturated compacted clay with different initial densities were performed using a suction‐controllable triaxial apparatus, to measure the stress–strain–volume change in different stress paths and wetting paths. The model has well‐predicting capabilities to reproduce the mechanical behaviour of specimens compacted under different conditions not only in isotropic compression but also in triaxial compression and triaxial extension. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献