本文關鍵詞：青藏高原及周邊區(qū)域冰芯放射性同位素定年及近兩百年來環(huán)境記錄研究　出處：《南京大學》2017年博士論文　論文類型：學位論文

  更多相關文章： 青藏高原冰芯 放射性同位素定年(AMS~(14)C ~(210)Pb ~3H) 重金屬Cd 人工核素~(239 240)Pu~(236)U

【摘要】：冰芯是研究過去氣候與環(huán)境變化的良好載體,中緯度地區(qū)的山地冰川更加接近人類活動密集區(qū),該地區(qū)的冰芯記錄能更好地揭示人類活動對于地球環(huán)境的影響。而冰芯定年是冰芯研究的基礎,傳統(tǒng)的數(shù)年層定年方法由于受冰芯減薄作用影響對冰芯下部樣品不再適用,參考層位法能提供的參考年份有限,放射性210Pb定年的年齡上限為150年。基于上述定年方法的局限性,AMS14C定年的方法被應用到冰川定年中。本文通過提取冰芯樣品中的不溶性有機碳質氣溶膠,對青藏高原西昆侖216.61米崇測透底冰芯(35°14'56.58"N,81°5'27.7"E;海拔6105米)、135.8米崇測透底冰芯(35°14'6.11"N,81°6'50.62"E;海拔6010米)、57.6米廟兒溝透底冰芯(43°03'19"N,94°19'21"E;海拔4512米)和95.8米東絨布透底冰芯(28°01'05"N,86°57'52"E;海拔6518米)進行了底部AMS14C定年研究。并采用放射性210Pb定年和3H核試驗參考層定年方法,對216.61米崇測冰芯上部進行了定年研究。另外對東天山廟兒溝冰芯1776-2004年間高分率的重金屬元素Cd記錄和1940-1975年全球核試驗主要時期的人工核素239.240Pu和236U記錄進行了分析。論文研究的主要結論如下:(1)216.61米崇測透底冰芯30-216米深度范圍內22個AMS14C結果表明該支冰芯涵蓋了距今4600多年的歷史記錄,其底部215.08-216.04米處14C年齡為4590±241 cal.a BP,與135.8米崇測透底冰芯的底部134.32-135.04米處14C年齡6253±227 cal.a BP具有可比性。57.6米廟兒溝透底冰芯底部樣品的AMS14C年齡為5388±359 cal.a BP(對應深度56.2-57.1m),95.8米東絨布透底冰芯底部樣品的AMS14C年齡為6724±430cal.a BP(對應深度95.4-95.8 m)。結合青藏高原已發(fā)表的普若崗日冰芯和敦德冰芯的底部14C年齡結果,顯示目前青藏高原北、中、南部透底深冰芯的底部年齡均未超過7000 a BP,表明青藏高原地區(qū)可能保存的長時間尺度冰芯記錄不超過全新世大暖期。(2)216.61米崇測冰芯3H核試驗1963年峰值出現(xiàn)在冰芯21.4米處,峰值活度為3237±89TU。該地區(qū)表層210Pb比活度為236±33 mBq/kg,210Pb定年結果表明該支冰芯0-44米深度涵蓋了過去122年(1891-2013年)的歷史記錄。3H核試驗參考層位法的定年結果與210Pb定年結果一致。(3)20世紀40年代以來,廟兒溝冰芯中大氣沉降的Cd主要來自于人類源的貢獻,20世紀40年代以前,則主要來自于自然源的貢獻。廟兒溝地區(qū)Cd的自然來源主要是土壤和巖石粉塵的影響。人類活動的影響在20世紀中后期尤為明顯,主要源于廟兒溝上風向的東歐及中亞地區(qū)國家的礦業(yè)生產、金屬冶煉制造等工業(yè)活動的影響。與北半球其他地區(qū)記錄相比,廟兒溝冰芯Cd濃度在21世紀初的迅速增加,則源于我國能源和經濟需求伴隨著的新疆地區(qū)的工業(yè)活動的快速發(fā)展,進而向大氣中排放了大量的含Cd物質。(4)大氣核試驗主要時期,廟兒溝冰芯的239Pu沉積總通量為1.55*109 atoms·cm-2,與世界上其他地區(qū)的大部分冰芯記錄相比略高,符合人工核素Pu的全球沉降中緯度地區(qū)偏高的分布特征。北半球不同冰芯記錄的239Pu沉積總通量分布具有差異性,原因是不同地區(qū)干濕沉降條件和后沉積環(huán)境有所差異以及不同研究區(qū)的貢獻源區(qū)也不盡相同。240Pu/239Pu同位素比率的平均值為0.18±0.02,表明該地區(qū)的人工核素沉降來源于全球大氣傳輸沉降的影響,其近源地區(qū)如我國的羅布泊核試驗點沒有影響到該地區(qū)。廟兒溝冰芯的236U沉積總通量為3.5*108 atoms·cm-2,與目前唯一已發(fā)表的北極Svalbard冰蓋(79.83°N,24.02°E;海拔750米)地區(qū)的冰芯記錄結果1.6*108atoms·cm-2具有可比性。廟兒溝冰芯236U/239Pu比率介于0.12-0.43之間(平均值0.27),與其他地區(qū)已發(fā)表的記錄具有一致性。
[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foundation of the traditional ice core study, several years of dating methods due to ice layer the thinning effect is no longer applicable to lower ice core samples, reference horizon method can provide the reference year, radioactive 210Pb dating of the age limit is 150 years.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.

【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：P597;P532

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