| 引用本文: | 史运坤，鄂崇毅，张晶，孙满平，李萍，彭强，徐春霞，谢丽倩，张兆康.2021.青海湖地区不同海拔黄土磁化率环境指示意义[J].地球环境学报,12(3):256-268 |
| SHI Yunkun, E Chongyi, ZHANG Jing, SUN Manping, LI Ping, PENG Qiang, XU Chunxia, XIE Liqian, ZHANG Zhaokang.2021.Environmental implications of magnetic susceptibility of the loess at different altitudes in Qinghai Lake area[J].Journal of Earth Environment,12(3):256-268 |
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| 摘要: |
| 青藏高原黄土蕴含丰富的古气候信息，但青海湖地区黄土中磁化率指示意义尚不明确，鉴于粒度指标意义明晰，对青海湖地区多个黄土剖面进行磁化率 — 粒度相关性研究，探究磁化率的指示意义，结果表明不同海拔磁化率存在差异：（1）低于3300 m时，磁化率和粒度对古环境指示作用较好，即气候暖湿，成壤作用增强，黏粒增加，强磁性矿物增加，磁化率升高，气候冷干时相反；海拔改变导致土壤环境变化，磁化率随海拔上升而增加。（2）高于3400 m时，粒度的古环境指示作用明确但磁化率不敏感，可能因为高海拔地区土壤易处于还原环境，强磁性矿物被溶解导致磁化率异常，磁化率随海拔上升而降低。 |
| 关键词: 青海湖 黄土 磁化率 粒度 海拔效应 |
| DOI：10.7515/JEE212006 |
| CSTR：32259.14.JEE212006 |
| 分类号: |
| 基金项目:国家自然科学基金项目（41761042，41361047）；青海省科技厅自然科学基金项目（2021-ZJ-918）；中国科学院“西部之光”项目（CAS-901）；青海省创新平台建设专项（2020-ZJ-Y06） |
| 英文基金项目:National Natural Science Foundation of China (41761042, 41361047); Natural Science Foundation of Qinghai Provincial Science and Technology Department (2021-ZJ-918); CAS “Light of West China” Program (CAS-901); Science and Technology Innovation Platform Project of Qinghai Province (2020-ZJ-Y06) |
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| Environmental implications of magnetic susceptibility of the loess at different altitudes in Qinghai Lake area |
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SHI Yunkun, E Chongyi, ZHANG Jing, SUN Manping, LI Ping, PENG Qiang, XU Chunxia, XIE Liqian, ZHANG Zhaokang
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1. Key Laboratory of Tibetan Plateau Land Surface Processes and Ecological Conservation (Ministry of Education), Qinghai Normal University, Xining 810008, China
2. Qinghai Province Key Laboratory of Physical Geography and Environmental Process, College of Geographical Science, Qinghai Normal University, Xining 810008, China
3. Academy of Plateau Science and Sustainability, People’s Government of Qinghai Province and Beijing Normal University, Xining 810008, China
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| Abstract: |
| Background, aim, and scope The loess deposit on the Qinghai-Tibet Plateau contains abundant information regarding climate evolution. The Qinghai Lake, the largest saline lake in China, is important to maintain the ecological security in the northeast of Qinghai-Tibet Plateau. The environmental significance of the grain size (GS) of loess is clear in Qinghai Lake area, but that of the magnetic susceptibility (MS) is equivocal. Therefore, in this study we aimed to explore the environmental significance of the MS of loess by analyzing the relationship between MS and GS. Materials and methods We selected seven typical loess profiles and tested the GS and MS of 301 samples; the correlation between these two indexes was analyzed using SPSS 25.0. Results The correlation between MS and GS of loess in Qinghai Lake area varies with altitude. At low altitudes (＜3300 m), there is a strong correlation between MS and clay (＜4 μm) component content area. MS increases with elevation; but at high altitudes (＞3400 m), the correlation is poor and MS decreases with elevation. Discussion The soil environment varies with altitude. At low altitudes, the temperature, precipitation and soil moisture content are suitable; thus, MS increases with elevation. Therefore, the paleoenvironmental significance of MS and GS are similar to the Central Loess Plateau. Under warm and humid climate conditions, the pedogenesis is strong, with the clay particles increasing and strongly magnetic minerals augmenting, which results in more fine particles being carried by wind; thus, MS increases. Under cold and dry climatic conditions, the wind carries more coarse particles, the sand content increases, and the clay content decreases. Moreover, the pedogenesis is restricted, and the increase of magnetic minerals is limited; thus, MS decreases. The correlation between MS and clay content is poor in high altitude area. This could be attributed to increased precipitation, lower temperature, lower evaporation, higher soil moisture content, longer freeze-thaw time, and reductive soil environment, that contribute to the dissolution of strongly magnetic minerals; thus, MS unexpectedly decreases with elevation, and is a weak environmental index. Conclusions In the loess deposits of the Qinghai Lake area, the MS and GS indexes of the low altitude profiles (＜3300 m) can better indicate paleoenvironmental changes; however, MS becomes an invalid environmental indicator in high altitude areas (＞3400 m) due to unsuitable soil environments in such altitudes. Recommendations and perspectives In the loess sections of Qinghai Lake area, there may be an “altitude effect” on the MS index. Therefore, when using the MS index to reconstruct the paleoclimate of the region, we should consider the influence of various factors such as soil moisture content. |
| Key words: Qinghai Lake loess magnetic susceptibility particle size altitudinal effect |
