福建仙云洞现代次生碳酸盐团簇同位素特征与温度重建  

Clumped isotope characteristics and temperature reconstruction of carbonate in modern speleothems of Xianyun cave in Fujian

作　　者：杜垚华 李苗发 雷国良[1,2,3] 王芳[1,2] 于源[1,2] 江戈平[1,2] 姜修洋 蔡炳贵 DU Yaohua;LI Miaofa;LEI Guoliang;WANG Fang;YU Yuan;JIANG Geping;JIANG Xiuyang;CAI Binggui(Key Laboratory for Humid Subtropical Eco-geographical Processes of the Ministry of Education,Fujian Normal University,Fuzhou 350117,Fujian;School of Geographical Sciences,Fujian Normal University,Fuzhou 350117,Fujian;Stable Isotope Center,Fujian Normal University,Fuzhou 350117,Fujian)

机构地区：[1]福建师范大学湿润亚热带生态地理过程教育部重点实验室,福建福州350117 [2]福建师范大学地理科学学院,福建福州350117 [3]福建师范大学稳定同位素中心,福建福州350117

出　　处：《第四纪研究》2023年第5期1343-1353,共11页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41977390);云南省高原地理过程与环境变化重点实验开放基金项目(批准号:PGPEC201801)共同资助。

摘　　要：碳酸盐团簇同位素(Δ47)是基于碳酸盐中13C-18O丰度相较于其随机分布状态的偏离程度对温度进行估算的新型测温技术。洞穴石笋沉积过程复杂,部分石笋受动力分馏作用影响导致其碳酸盐Δ47偏离平衡体系,这些因素增大了利用石笋碳酸盐Δ47定量重建古温度的难度。本研究以典型东亚夏季风影响区的福建仙云洞为研究对象,通过对该洞现代次生碳酸盐样品的采集和稳定同位素组成的测定,探讨研究区现代次生碳酸盐Δ47特征及其重建温度的可靠性。研究结果表明:1)仙云洞5个现代次生碳酸盐样品的Δ47和δ18O结果均较为集中,而δ13C差异较大,这种样品间差异与共性并存的特征表明本研究所选样品具有代表性;2)仙云洞5个现代次生碳酸盐样品的Δ47值在0.702‰~0.720‰范围内波动,实测温度与基于平衡体系下建立的团簇同位素温度转换方程计算的温度结果较为一致,揭示出该洞穴现代次生碳酸盐Δ47接近热力平衡,不存在显著的动力分馏;3)基于洞穴次生碳酸盐的团簇同位素温度和δ18O值,推算出对应的滴水δ18O值介于-8.0‰~-7.6‰之间,这与长期监测的仙云洞滴水δ18O结果较为吻合,表明仙云洞现代次生碳酸盐氧同位素接近同位素平衡。本文研究结果为重建区域古温度和古降水提供了证据支撑。Carbonate clumped isotope thermometry is a relatively new paleotemperature tool based on measurements of the degree of ordering of 13C-18O bonding to each other in carbonate mineral lattices.Speleothems are important archives in continental paleoenvironment because they have the advantages of precise 230Th dating,high-resolution,long-spanning and so on.However,there is evidence that speleothems grow out of isotopic equilibrium due to a complex deposition process,and the application of clumped-isotope thermometry to speleothem records is currently limited by the scarcity of understanding of these isotopic disequilibrium.Here we reportΔ47 values measured in five modern natural speleothems from two locations in Xianyun cave(China),and attempt to understand the degree of speleothems out of thermodynamic equilibrium in Xianyun cave.Xianyun cave(25.55°N,116.98°E;968 m above sea level)is located in Longyan,Fujian Province,Southeastern China,which is a front area affected by the East Asian monsoon.It has only one entrance(ca.2 m in height,ca.1 m in width)with proven total length of about 2470 m and the distribution area of ca.15000 m2.The air temperature and relative humidity inside the cave are 17℃and ca.100%throughout the year,respectively.Five natural,actively growing speleothems were sampled from two settings within Xianyun cave in 2017.Three of them(CXYD-A,CXYD-B2 and XY-2)were obtained from ca.650 m behind the entrance to the southern branch of the cave,and their lengths were 4.5 cm,9.0 cm and 2.0 cm,respectively.The samples of XY-3 and XY-4 were collected at the bifurcation of two main cave branches,which are ca.170 m away from the entrance,and their thicknesses are 2 cm and 3 cm,respectively.In addition,drip water from CXYD-A,CXYD-B2 and XY-4 was also collected for stable isotope analyses of water oxygen.Theδ13C,δ18OC andΔ47 measurements were performed using a dual inlet mass spectrometry(IRMS,Thermo ScientificTM 253 Plus),and theδ18OW values of drip water were measured using a Picarro L2140-ICRDS.Theδ1

关 键 词：团簇同位素 氧同位素 仙云洞 洞穴次生碳酸盐 温度 

分 类 号：P597.2[天文地球—地球化学] X143[天文地球—地质学]