青藏高原及周边区域冰芯放射性同位素定年及近两百年来环境记录研究

发布时间：2018-01-14 00:23

本文关键词：青藏高原及周边区域冰芯放射性同位素定年及近两百年来环境记录研究　出处：《南京大学》2017年博士论文　论文类型：学位论文

【摘要】：冰芯是研究过去气候与环境变化的良好载体,中纬度地区的山地冰川更加接近人类活动密集区,该地区的冰芯记录能更好地揭示人类活动对于地球环境的影响。而冰芯定年是冰芯研究的基础,传统的数年层定年方法由于受冰芯减薄作用影响对冰芯下部样品不再适用,参考层位法能提供的参考年份有限,放射性210Pb定年的年龄上限为150年。基于上述定年方法的局限性,AMS14C定年的方法被应用到冰川定年中。本文通过提取冰芯样品中的不溶性有机碳质气溶胶,对青藏高原西昆仑216.61米崇测透底冰芯(35°14'56.58"N,81°5'27.7"E;海拔6105米)、135.8米崇测透底冰芯(35°14'6.11"N,81°6'50.62"E;海拔6010米)、57.6米庙儿沟透底冰芯(43°03'19"N,94°19'21"E;海拔4512米)和95.8米东绒布透底冰芯(28°01'05"N,86°57'52"E;海拔6518米)进行了底部AMS14C定年研究。并采用放射性210Pb定年和3H核试验参考层定年方法,对216.61米崇测冰芯上部进行了定年研究。另外对东天山庙儿沟冰芯1776-2004年间高分率的重金属元素Cd记录和1940-1975年全球核试验主要时期的人工核素239.240Pu和236U记录进行了分析。论文研究的主要结论如下:(1)216.61米崇测透底冰芯30-216米深度范围内22个AMS14C结果表明该支冰芯涵盖了距今4600多年的历史记录,其底部215.08-216.04米处14C年龄为4590±241 cal.a BP,与135.8米崇测透底冰芯的底部134.32-135.04米处14C年龄6253±227 cal.a BP具有可比性。57.6米庙儿沟透底冰芯底部样品的AMS14C年龄为5388±359 cal.a BP(对应深度56.2-57.1m),95.8米东绒布透底冰芯底部样品的AMS14C年龄为6724±430cal.a BP(对应深度95.4-95.8 m)。结合青藏高原已发表的普若岗日冰芯和敦德冰芯的底部14C年龄结果,显示目前青藏高原北、中、南部透底深冰芯的底部年龄均未超过7000 a BP,表明青藏高原地区可能保存的长时间尺度冰芯记录不超过全新世大暖期。(2)216.61米崇测冰芯3H核试验1963年峰值出现在冰芯21.4米处,峰值活度为3237±89TU。该地区表层210Pb比活度为236±33 mBq/kg,210Pb定年结果表明该支冰芯0-44米深度涵盖了过去122年(1891-2013年)的历史记录。3H核试验参考层位法的定年结果与210Pb定年结果一致。(3)20世纪40年代以来,庙儿沟冰芯中大气沉降的Cd主要来自于人类源的贡献,20世纪40年代以前,则主要来自于自然源的贡献。庙儿沟地区Cd的自然来源主要是土壤和岩石粉尘的影响。人类活动的影响在20世纪中后期尤为明显,主要源于庙儿沟上风向的东欧及中亚地区国家的矿业生产、金属冶炼制造等工业活动的影响。与北半球其他地区记录相比,庙儿沟冰芯Cd浓度在21世纪初的迅速增加,则源于我国能源和经济需求伴随着的新疆地区的工业活动的快速发展,进而向大气中排放了大量的含Cd物质。(4)大气核试验主要时期,庙儿沟冰芯的239Pu沉积总通量为1.55*109 atoms·cm-2,与世界上其他地区的大部分冰芯记录相比略高,符合人工核素Pu的全球沉降中纬度地区偏高的分布特征。北半球不同冰芯记录的239Pu沉积总通量分布具有差异性,原因是不同地区干湿沉降条件和后沉积环境有所差异以及不同研究区的贡献源区也不尽相同。240Pu/239Pu同位素比率的平均值为0.18±0.02,表明该地区的人工核素沉降来源于全球大气传输沉降的影响,其近源地区如我国的罗布泊核试验点没有影响到该地区。庙儿沟冰芯的236U沉积总通量为3.5*108 atoms·cm-2,与目前唯一已发表的北极Svalbard冰盖(79.83°N,24.02°E;海拔750米)地区的冰芯记录结果1.6*108atoms·cm-2具有可比性。庙儿沟冰芯236U/239Pu比率介于0.12-0.43之间(平均值0.27),与其他地区已发表的记录具有一致性。
[Abstract]:Ice core research on the past climate and environmental changes in good carrier, mid latitude mountain glaciers closer to the intensive areas of human activity, the area of the ice core records can better reveal the influence of human activity on the earth's environment. And the ice core dating is the foundation of the traditional ice core study, several years of dating methods due to ice layer the thinning effect is no longer applicable to lower ice core samples, reference horizon method can provide the reference year, radioactive 210Pb dating of the age limit is 150 years. The limitations of the dating method based on the method of AMS14C dating was applied in this paper. The glacier dating through the extraction of insoluble organic carbonaceous aerosol ice in the sample, in the western Kunlun plateau 216.61 meters high (35 degrees 14'56.58 measured through the end of the ice core "N, 81" 5'27.7 E "; at an elevation of 6105 meters, 135.8 meters high) measured through the end of ice (35" 14'6.11 "N, 81" 6'50.62 "E; 6010 meters above sea level) Miaoergou, 57.6 meters through the end of ice (43 "03'19" N, 94 "19'21" E; 4512 meters above sea level) and 95.8 meters (28 degrees 01'05 flannelette through the end of ice "N, 86" 57'52 "E; 6518 meters above sea level) was made in the paper at the bottom of the AMS14C. And using radioactive 210Pb dating and 3H the nuclear test reference layer dating methods, the dating of the 216.61 metre Chongce ice core. In addition to the upper Cd records of heavy metal elements in East Tianshan Miaoergou cores during 1776-2004 high rate and the main period of global nuclear test 1940-1975 artificial nuclide 239.240Pu and 236U records were analyzed. The main conclusions of this paper are as follows: (1) 216.61 meters 30-216 meters depth measurement through the end of the ice core worship in the range of 22 AMS14C results show that the ice cores covering 4600 years ago to the historical record, the bottom of 215.08-216.04 meters 14C age of 4590 + 241 cal.a BP, and 135.8 meters at the bottom of the 134.32-135.04 ice core Chong measured through the end of 14 meters The C age of 6253 + 227 cal.a BP comparable.57.6 m Miaoergou ice core samples of AMS14C through the end of the bottom age of 5388 + 359 cal.a BP (56.2-57.1m, 95.8 meters in depth) at the bottom of the ice core samples through the end of cloth AMS14C age of 6724 430cal.a BP (95.4-95.8 m in depth). Combined with the Tibetan Plateau have been published in general if the bottom of the 14C age results Kangri ice cores and Dunde ice core, showing the North Qinghai Tibet Plateau, and the southern end at the bottom of the deep ice core age was less than 7000 a BP, showed that long time scale ice core record Tibet Plateau area may save less than the Holocene Megathermal. (2) 216.61 meters Chongce ice core 3H the 1963 nuclear test peak in the ice 21.4 meters, the peak of activity was 3237 + 89TU. of the surface area of the specific activity of 210Pb was 236 + 33 mBq/kg, 210Pb dating results show that the ice core 0-44 meters depth covers over the past 122 years (1891-2013 years). The history of.3H nuclear test reference horizon method dating results and 210Pb dating results. (3) since 1940s, atmospheric deposition Cd Miaoergou in ice mainly from human sources, before 1940s, the main contribution comes from natural sources. Natural sources of the Miaoergou area is mainly Cd effect of soil and rock dust. The impact of human activities in late twentieth Century is particularly evident, the main source of mining production in the country on the Miaoergou direction of Eastern Europe and Central Asia, the influence of metal smelting and manufacturing industrial activities. Compared with other parts of the northern hemisphere ice core records, the Miaoergou Cd concentration increased rapidly in twenty-first Century at the beginning, the rapid development of economy and is derived from the energy demand of our country with the Xinjiang area of industrial activity, and emission of Cd containing a lot of material into the atmosphere. (4) the main period of atmospheric nuclear tests, Temple The 239Pu ice core ditch total sediment flux is 1.55*109 atoms cm-2, compared with most of the ice core records in other parts of the world is slightly higher in the high latitude region conforms to the global settlement distribution of radionuclide Pu. 239Pu deposition flux distribution in the northern hemisphere in different ice core records with differences. The reason is the average value of dry and wet deposition in different regions after the conditions and sedimentary environment differences and contributions of different source regions in the study area are not the same.240Pu/239Pu isotope ratio is 0.18 + 0.02, showed that the effect of artificial radioactive nuclide in the area of settlement from the global atmospheric transport sedimentation, the near source regions such as the Lop Nor nuclear test in China did not affect the temple area. Er Gou ice core deposition flux is 3.5*108 atoms 236U cm-2, and is currently the only published Svalbard in the Arctic ice cap (79.83 ~ N, 24.02 ~ E; 750 meters above sea level) in ice core records. The fruit 1.6*108atoms. Cm-2 has comparability. The 236U/239Pu ratio of the Mier gully ice core is between 0.12-0.43 (average value 0.27), which is consistent with the published records in other regions.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P597;P532

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