排序方式: 共有46条查询结果,搜索用时 15 毫秒
1.
中国东部季风区末次冰期以来古气候模拟 总被引:5,自引:0,他引:5
通过对我国东部季风区现代青土样品孢粉组合与气候因子间的回归分析,分别建立了孢粉组合与一月,七月气温和年降水量的转换函数,进而建立了本区末次冰期以来的孢粉-气候数据库,模拟末次冰期盛冰期,消冰期,全新世前北方期-北方期,大西洋期,亚北方期等五个古气候期的冬季和夏季温度场,降水场。 相似文献
2.
Identification of key parameters controlling dissolved oxygen migration and attenuation in fractured crystalline rocks 总被引:1,自引:0,他引:1
In the crystalline rocks of the Canadian Shield, geochemical conditions are currently reducing at depths of 500-1000 m. However, during future glacial periods, altered hydrologic conditions could potentially result in enhanced recharge of glacial melt water containing a relatively high concentration of dissolved oxygen (O2). It is therefore of interest to investigate the physical and geochemical processes, including naturally-occurring redox reactions, that may control O2 ingress. In this study, the reactive transport code MIN3P is used in combination with 2k factorial analyses to identify the most important parameters controlling oxygen migration and attenuation in fractured crystalline rocks. Scenarios considered are based on simplified conceptual models that include a single vertical fracture, or a fracture zone, contained within a rock matrix that extends from the ground surface to a depth of 500 m. Consistent with field observations, Fe(II)-bearing minerals are present in the fractures (i.e. chlorite) and the rock matrix (biotite and small quantities of pyrite). For the parameter ranges investigated, results indicate that for the single fracture case, the most influential factors controlling dissolved O2 ingress are flow velocity in the fracture, fracture aperture, and the biotite reaction rate in the rock matrix. The most important parameters for the fracture zone simulations are flow velocity in the individual fractures, pO2 in the recharge water, biotite reaction rate, and to a lesser degree the abundance and reactivity of chlorite in the fracture zone, and the fracture zone width. These parameters should therefore receive increased consideration during site characterization, and in the formulation of site-specific models intended to predict O2 behavior in crystalline rocks. 相似文献
3.
4.
5.
6.
底栖有孔虫碳同位素(δ13C)是研究地质历史时期碳循环和大洋深部环流的重要指标。通过汇编42条过去130 ka以来底栖有孔虫的δ13C记录,建立全球大洋深部以及不同水团包括北大西洋深层水(NADW)和太平洋深层水(PDW)的δ13Cstack (数据存储格式为.xlsx),以及海洋同位素阶段(marine isotope stage,MIS)5-1期大西洋和印度-太平洋δ13C经向剖面,探索130 ka以来大洋无机碳δ13C的演变特征及其与碳循环和大洋深部经向环流的关联。结果表明全球碳同位素在冰期较低,间冰期较高,且大西洋振幅高于太平洋。末次盛冰期海水表层温度及海平面都比MIS 4期略低,但MIS 4期δ13C更偏负,其可能原因是北大西洋通风减弱增加了深海对大气CO2的固存,导致大气CO2浓度的降低。但该结论并未考虑南大洋其他生物化学过程,未来研究将重点探讨南大洋其他生物化学过程与碳循环的相互作用,进一步深化对这一复杂系统的理解。 相似文献
7.
环境监测是环境管理的基础性工作,污染源监测报告(数据)的有效性是保证环境执法严肃、公正的重要条件,也是是守法企业展示良好社会形象的基本保证。依照国家的相关规定,并结合行业技术规范的要求,探讨污染源监测报告的有效期问题,以利于相关各方严肃、科学、合理地使用污染源监测数据。 相似文献
8.
民国年间河南灾荒现象异常突出,虽与当时整体气候背景及河南特殊的地理特征相关,但灾荒背后的社会原因更应引起我们的关注。其主要表现为:一、社会经济乏力,百姓抗灾能力低;二、政治腐败,体现在政府的赋税名目繁多、政府官员失职渎职以及挪用、贪污河防公款等几个方面;三、战争与灾荒;四、帝国主义列强对中国的残酷掠夺。 相似文献
9.
10.