Study on dating method of 32Si in marine sediments
-
摘要: 天然32Si是宇宙射线成因的,随着降水进入湖泊或海洋,被硅质生物摄取后最终存在于生物硅中。32Si来源单一,生产速率相对恒定,半衰期为150 a,可测年的时间尺度为100~1 000 a,是该时间尺度最合适的测年核素,填补了百年到千年时间尺度测年方法的空白。本文建立了海洋沉积物32Si的测量方法,主要步骤为:(1)样品前处理;(2)生物硅的分离与纯化;(3)生物硅样品中磷的分离与纯化;(4)32P的制样与β计数测量。全程通过硅钼蓝和磷钼蓝分光光度法监测实验过程硅和磷的损失情况,对南沙海域采集的沉积物岩心进行研究,得到南沙海域沉积物岩心32Si的平均活度为16.60 mBq/kg,范围值为8.39~33.34 mBq/kg;32Si在SiO2中的平均比活度为0.356 Bq/kg,32Si的核素丰度平均值为1.29×10-16(32Si/SiO2);根据岩心32Si活度估算得深水区(水深1 335~1 537 m)和浅水区(121~141 m)岩心的沉积速率分别为0.106 cm/a、0.191 cm/a;根据32Si活度计算32Si的平均沉降通量为2.14×10-6 Bq/(cm2·a),与参考文献的结果较为吻合。Abstract: 32Si generates from the spallation reaction of cosmic rays and argon in atmosphere, which is ingested by siliceous organisms such as diatoms after falling into the lakes and sea from atmosphere. The cosmogenic radioactive isotope 32Si, with a half-life of approximately 150 a, represents an excellent dating tool for the age range of approximately 100-1 000 a. 32Si, with a single source and a constant production rate, is of importance to the ancient environments and paleoclimatology. The method of determining 32Si activity in the marine sediments was established. The main steps were as follows:(1) sample pretreatment; (2) separating and purifying biogenic silica; (3) separating and purifying phosphorus from biogenic silica; (4) preparation of phosphorus and counting 32P by β counter. The experimental process was monitored by acidic silicomolybdenum blue spectrophotometry and phosphomolybdenum blue spectrophotometry to control loss of silicon and phosphorus during the process. The specific activity of 32Si in sediments from Nansha sea area varies from 8.39 mBq/kg to 33.34 mBq/kg, with 16.60 mBq/kg as the mean value. The average specific activity of 32Si in SiO2 is 0.356 Bq/kg. The average specific abundance of 32Si in biogenic silica is 1.29×10-16 (32Si/SiO2). Sedimentary rates of sediment cores from deep water (1 335-1 537 m) and shallow water (121-141 m) are 0.106 cm/a and 0.191 cm/a respectively. The average setting flux of 32Si is 2.14×10-6 Bq/(cm2·a), within the range of references.
-
Key words:
- 32Si /
- biogenic silica /
- dating /
- Nansha sea area /
- sediment core
-
Morgenstern U, Geyh M A, Kudrass H R, et al. 32Si dating of marine sediments from Bangladesh[J]. Radiocarbon, 2001, 43(2B):909-916. Morgenstern U, Ditchburn R G, Vologina E G, et al. 32Si dating of sediments from Lake Baikal[J]. Journal of Paleolimnology, 2013, 50(3):345-352. 刘广山. 海洋放射年代学[M]. 厦门:厦门大学出版社, 2016. Liu Guangshan. Marine Radiochronology[M]. Xiamen:Xiamen University Press, 2016. Morgenstern U, Fifield L K, Zondervan A. New frontiers in glacier ice dating:measurement of natural 32Si by AMS[J]. Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms, 2000, 172(1/4):605-609. Einloth S, Ekwurzel B, Eastoe C, et al. 32Si as a potential tracer for century-scale recharge in semi-arid regions[J]. Geophysical Research Abstracts, 2003, 5:13164. DeMaster D J. The half life of 32Si determined from a varved Gulf of California sediment core[J]. Earth and Planetary Science Letters, 1980, 48(1):209-217. DeMaster D J, Cochran K J. Particle mixing rates in deep-sea sediments determined from excess 210Pb and 32Si profiles[J]. Earth and Planetary Science Letters, 1982, 61(2):257-271. Nijampurkar V N, Rao D K, Oldfield F, et al. The half-life of 32Si:a new estimate based on varved lake sediments[J]. Earth and Planetary Science Letters, 1998, 163(1/4):191-196. Suckow A, Morgenstern U, Kudrass H R. Absolute dating of recent sediments in the cyclone-influenced shelf area off Bangladesh:comparison of gamma spectrometric (137Cs, 210Pb, 228Ra), radiocarbon, and 32Si ages[J]. Radiocarbon, 2001, 43(2B):917-927. 刘存富, 王佩仪, 周炼, 等. 河北山前平原地下水32Si年龄初探[J]. 水文地质工程地质, 1999, 26(2):1-3, 9. Liu Cunfu, Wang Peiyi, Zhou Lian, et al. 32Si dating of piedmont plain groundwater in Hebei[J]. Hydrogeology and Engineering Geology, 1999, 26(2):1-3, 9. 周炼, 刘存富, 王佩仪. 地下水32Si年龄的测定方法——液体闪烁计数法[J]. 岩矿测试, 2000, 19(2):97-100. Zhou Lian, Liu Cunfu, Wang Peiyi. Dating of the groundwater by 32Si-liquid scintillation counting method[J]. Rock and Mineral Analysis, 2000, 19(2):97-100. 刘广山. 海洋放射性核素测量方法[M]. 北京:海洋出版社, 2006. Liu Guangshan. Measurement Methods of Radionuclides in the Sea[M]. Beijing:China Ocean Press, 2006. 陈锦芳. 厦门沿岸海域磷循环的宇生32P、33P示踪研究[D]. 厦门:厦门大学, 2006. Chen Jinfang. Study on cosmic-ray-produced 32P, 33P of phosphorus circulation in coastal waters of Xiamen[D]. Xiamen:Xiamen University, 2006. 石健, 王东升, 杭喻文. 不同条件对活性硅酸聚合的影响[C]//2014中国环境科学学会学术年会论文集(第五章). 成都:中国环境科学学会, 四川大学, 2014:6. Shi Jian, Wang Dongsheng, Hang Yuwen. Effects of different conditions on active silicic acid polymerization[C]//Academic Annual Conference Proceedings of Chinese Society for Environmental Science (chapter 5). Chengdu:Chinese Society for Environmental Science, Sichuan University, 2014:6. 詹晓青, 胡盼盼, 刘广山, 等. 南沙海域沉积物岩心生物硅和碳酸盐研究[J]. 海洋科学前沿, 2015, 2(3):53-63. Zhan Xiaoqing, Hu Panpan, Liu Guangshan, et al. The study of biogenic silica and carbonate in the sediment cores from Nansha Sea area[J]. Advances in Marine Sciences, 2015, 2(3):53-63. Kharkar D P, Turekian K K, Scott M R. Comparison of sedimentation rates obtained by 32Si and uranium decay series determinations in some siliceous Antarctic cores[J]. Earth and Planetary Science Letters, 1969, 6(1):61-68. Somayajulu B L K, Rengarajan R, Lal D, et al. GEOSECS Atlantic 32Si Profiles[J]. Earth and Planetary Science Letters, 1987, 85(4):329-342. Martins J M, Meybecks M, Nijampurkar V N, et al. 210Pb, 226Ra and 32Si in Pavin Lake (Massif Central, France)[J]. Chemical Geology:Isotope Geoscience Section, 1992, 94(3):173-181. Kharkar D P, Lal D, Somayayjulu B L K. Investigations in marine environments using radioisotope produced by cosmic rays[C]//Proceedings of International Symposiums for Radioactive Dating. Athens:IAEA, 1963:175-187. Kharkar D P, Nijampurkar V N, Lal D. The global fallout of Si32 produced by cosmic rays[J]. Geochimica et Cosmochimica Acta, 1966, 30(6):621-631. Somayajulu B L K, Rengarajan R, Lal D, et al. GEOSECS Pacific and Indian ocean 32Si profiles[J]. Earth and Planetary Science Letters, 1991, 107(1):197-216. 周鹏, 李冬梅, 刘广山, 等. 应用宇生放射性同位素硅-32示踪海洋过程的研究[J]. 同位素, 2015, 28(1):7-19. Zhou Peng, Li Dongmei, Liu Guangshan, et al. Study on a cosmic-ray-produced silicon-32 as a tracer for ocean processes[J]. Journal of Isotopes, 2015, 28(1):7-19. Franke T, Fröhlich K, Gellermann R, et al. 32Si in precipitation of Freiberg/GDR/[J]. Journal of Radioanalytical and Nuclear Chemistry, 1986, 103(1):11-17. Nijampurkar V N, Rao D K. Polar fallout of radionuclides 32Si, 7Be and 210Pb and past accumulation rate of ice at Indian station, Dakshin Gangotri, East Antarctica[J]. Journal of Environmental Radioactivity, 1993, 21(2):107-117. Craig H, Somayajulu B L K, Turekian K K. Paradox lost:silicon 32 and the global ocean silica cycle[J]. Earth and Planetary Science Letters, 2000, 175(3/4):297-308. 詹晓青. 南沙海域沉积物岩心生物硅和32Si研究[D]. 厦门:厦门大学, 2017. Zhan Xiaoqing. Study on biogenic silica and 32Si in the sediment cores of Nansha Sea Area[D]. Xiamen:Xiamen University, 2017. Lal D, Peters B. Cosmic ray produced radioactivity on the earth[M]//Sitte K. Kosmische Strahlung Ⅱ/Cosmic Rays Ⅱ. Berlin, Heidelberg:Springer, 1967:551-612. Somayajulu B L K, Lal D, Craig H. Silicon-32 profiles in the South Pacific[J]. Earth and Planetary Science Letters, 1973, 18(2):181-188. Lal D, Nijampurkar V N, Rajagopalan G, et al. Annual fallout of 32Si, 210Pb, 22Na, 35S and 7Be in rains in India[J]. Proceedings of the Indian Academy of Sciences-Section A. Part 2, Earth and Planetary Sciences, 1979, 88(1):29-40. Lal D, Somayajulu B L K. Some aspects of the geochemistry of silicon isotopes[J]. Tectonophysics, 1984, 105(1/4):383-397.
点击查看大图
计量
- 文章访问数: 405
- HTML全文浏览量: 22
- PDF下载量: 193
- 被引次数: 0