Knowledge Resource Center for Ecological Environment in Arid Area
| 内蒙古达里湖末次冰消期以来的环境磁学研究 | |
| 其他题名 | Environmental magnetism of Dali Lake sediments in Inner Mongolia since the last deglaciation |
| 刘素贞 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 邓成龙 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 两万年以来的古气候快速波动是全球变化研究的一个重要方面。其中，末次冰消期的快速气候波动是地球极端冷暖气候之间的转变过程的优良载体。而全新世暖期(Holocene Warm Period，HWP)及其增温过程中的地质、生物记录对揭示当时的气候、环境和生态过程具有重要意义，对研究地史热期地球气候、环境的演化以及生物对环境变化的响应具有重要价值。我国华北、西北的东亚夏季风边缘区，属于亚洲内陆半干旱气候带，对气候、环境变化非常敏感。本论文选取内蒙古达里湖末次冰消期以来的岩芯样品，开展了系统的环境磁学研究。结合电子显微镜、X射线衍射等方法，得到下列结论：达里湖HWP的磁性矿物以生物成因的磁铁矿（磁小体化石）为主。这一生物磁学信号是磁小体化石产量而非溶解的变化。磁小体化石的含量受控于湖泊中的营养供应。HWP期间伴随温度升高、降水增加而形成的强烈地表径流向湖泊中输送了大量有利于趋磁细菌繁殖和矿化的营养物质，从而形成了强烈的生物磁学信号。磁小体化石含量的变化记录了达里湖地区HWP从开始到结束的精细过程。9.8 ka磁小体化石含量的快速升高可能代表HWP的开始；7.6 ka磁小体化石含量的再次快速升高可能代表地表径流从温度较低的冰雪融水向温度较高的季风降水的转变；而5.9 ka磁小体化石含量的急剧降低则可能代表HWP的突然结束。达里湖末次冰消期的沉积序列可以分为四段。其中Unit 1 (15.90–15.32 ka)种磁性矿物主要是近似单畴（SD）的钛磁铁矿颗粒。Unit 1对应于末次冰盛期之后的初始冰消阶段，区域气候条件仍处于冷干状态。在地表的冻融过程中，流域的玄武岩基岩被侵蚀并搬运至湖泊中沉积下来。Unit 2 (15.32–12.67 ka)和Unit 3 (12.67–11.56 ka)中磁性矿物为准单畴（PSD）颗粒的（钛）磁铁矿。由于冰消作用开始，Unit 2和Unit 3中磁性矿物主要是来自沉积盆地表层的土壤，并且分别记录了B?lling-Aller?d暖期和Younger Dryas冷事件。本论文在达里湖发现的磁小体化石很可能是亚洲内陆干旱、半干旱区首例地史热期的生物磁学响应记录。我们的结果表明，磁小体化石有可能作为指示地史热期的有效物理指标。 |
| 英文摘要 | Paleoclimate variations during the past 20000 years have been an important aspect in the study of global changes. The fluctuations during the last deglaciation are highly valuable for understanding rapid climatic changes and mechanisms during extremely variable conditions. The Holocene Warm Period (HWP) provides insights into the climate system and biotic responses to environmental variability during geological thermal events and thus serves as an excellent analogue for future global climate changes Dali Lake (43°13′–23′ N, 116°29′–45′ E) inInner Mongolia is located at the East Asian Summer Monsoon limit, and is therefore very sensitive to Quaternary climate changes. In this study, we present a high-resolution environmental magnetic record since the last deglaciation based on DL04 core sediments in Dali Lake. The rock magnetic measurements include hysteresis loops, isothermal remanent magnetization (IRM) acquisition and direct current (DC) demagnetization curves, first-order reversal curves, temperature-dependent magnetic susceptibilities (c-T curves), temperature-dependent zero-field cooling IRM curves. These magnetic measurements are supplemented by scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The 11.83-m core DL04 was drilled in 2004, and covered the past 15.9 ka. Our The main conclusions include are as follows: The 11.83-m core DL04 was drilled in 2004, and covered the past 15.9 ka. The main conclusions are as follows:The magnetic series during the last deglaciation in Dali Lake were divided into four units: Unit 1 (15.90–15.32 ka) is magnetically dominated by SD-like titanomagnetite from erosion of bedrock basalt during the period right after the Last Glacial Maximum, when ice cover under cold and dry conditions dominates the Dali Lake area. Magnetic minerals in Unit 2 (15.32–12.67 ka) and Unit 3 (12.67–11.56 ka) are mainly PSD (titano) magnetite from erosion of surface soils in the lake catchment. Unit 2 and Unit 3 coincide within time error with the B?lling-Aller?d warm period and Younger Dryas cold event, respectively.Magnetic minerals during the HWP are dominated by biogenic magnetite (magnetofossils) produced by magnetotactic bacteria (MTB) in the lake.The magnetofossil concentration in Dali Lake during HWP was controlled by production rather than dissolution. The warm and wet HWP conditions were favourable for nutrition supply, which is indispensable for MTB proliferation and magnetosome production. Therefore, the changes in magnetofossil abundance in Dali Lake document the detailed process of HWP in the lake area. The pronounced increase of magnetofossil concentrations at ~9.8 ka and decrease at ~5.9 ka in Dali Lake coincided respectively with the onset and termination of the HWP, and are respectively linked to increased nutrient supply due to postglacial warming and poor nutrition due to drying at ~6 ka in the Asian interior. The two-stage transition at ~7.7 ka correlates well with increased organic carbon in middle HWP and suggests that improved climate conditions, leading to high quality nutrient influx, fostered magnetofossil proliferation. Overall, the DL04 core records paleoclimatic and paleoenvironmental processes since the last deglaciation in the Dali Lake, eastern-central Inner Mongolia, including the B?lling-Aller?d warm period, the Younger Dryas cold event, and the HWP. Specifically, this study has recovered the first magnetofossil record during the HWP in the semi-arid East Asia. Our findings suggest that magnetofossil abundance is a potential effective indicator of hyperthermal events in geological times, at least for the HWP. |
| 中文关键词 | 东亚季风边缘区 ; 环境磁学 ; 磁小体化石 ; 全新世暖期 ; 末次冰消期 |
| 英文关键词 | East Asian monsoon limit environmental magnetism magnetofossil Holocene Warm Period the last deglaciation |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 地球动力学 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287672 |
| 推荐引用方式 GB/T 7714 | 刘素贞. 内蒙古达里湖末次冰消期以来的环境磁学研究[D]. 中国科学院大学,2016. |
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