共和盆地更尕海湖泊现代水环境与碳酸盐碳氧同位素组成变化  

Variations in carbon and oxygen isotopes of carbonate and water environments: A case study from Genggahai Lake, northeastern Qinghai-Tibetan Plateau

作　　者：金彦香[1] 强明瑞[1] 刘英英[1] 李渊[1] 李昊[1] 李丰山[1] 

机构地区：[1]兰州大学西部环境教育部重点实验室,兰州730000

出　　处：《科学通报》2015年第9期847-856,共10页Chinese Science Bulletin

基　　金：国家自然科学基金(41271219);国家重点基础研究发展计划(2012CB956102);高等学校博士学科点专项科研基金(20130211110035);兰州大学中央高校基本科研业务费专项(lzujbky-2014-259;lzujbky-2014-261)资助

摘　　要：通过分析更尕海轮藻碳酸盐结壳、软体动物壳体等碳氧同位素的季节变化,结合湖水溶解无机碳（DIC）碳同位素（δ13CDIC）和湖水氧同位素（δ18OLake）,探讨其与现代湖泊水体环境的关系.结果表明,5~8月,轮藻植物生长速率约为5~6 cm/月;期间,沉水植物强烈的光合作用和碳酸盐的析出导致湖水pH升高,同时湖水DIC和Ca2＋含量显著下降.结合流域水体氧同位素、气温和降水量等观测资料,指出更尕海湖泊水位季节变化是区域降水量与蒸发作用平衡的结果;湖水氧同位素组成主要受入湖水氧同位素组成、湖泊内蒸发过程和降水量等的影响.软体动物壳体氧、碳同位素组成可分别代表δ18OLake与δ13CDIC的年际变化.然而,轮藻结壳氧同位素与δ18OLake之间非平衡分馏效应显著,有待于进一步开展工作.Isotopes of authigenic carbonate from lake sediments have great potential to decipher climatic changes over geologic periods. However, the climatic significance of proxies needs further verification. Genggahai Lake is in the central Gonghe Basin on the northeastern Qinghai-Tibetan Plateau. The lake is currently dominated by various submerged plants and is favorable for the formation of biogenic carbonates. Over the past two years, we have monitored changes in chemical and physical properties of lake water and analyzed isotopic compositions of carbonates, including stem incrustations and mollusk shells. In combination with oxygen isotope changes of the lake water（δ18O Lake） and water bodies in the study area, seasonal changes in isotopes of carbonates were investigated. The growth of Chara spp. was found to be seasonal, with maximum growth rate in summer. From May through August, the growth rate of Chara spp. was 5–6 cm per month. During this period, p H values of lake water increased while dissolved inorganic carbon（DIC） and calcium ions（Ca2＋） decreased, as a result of intense photosynthesis and calcification during the growth season of submerged plants. Seasonal fluctuations of lake level were mainly controlled by regional rainfall and lake evaporation. Changes in δ18O Lake are attributed to variations of groundwater δ18O, evaporation processes, and/or regional precipitation. Because of the long growing season and slow calcification process of mollusk shells, oxygen stable isotope ratios in the shells（δ18O Shell） were mainly influenced by δ18O Lake. Carbon stable isotope ratios in the shells（δ13C Shell） were primarily affected by the carbon isotope of DIC（δ13C DIC）. There were no significant seasonal fluctuations in δ18O Shell and δ13C Shell. Therefore, δ18O Shell and δ13C Shell indicated annual variations of δ18O Lake and δ13C DIC, respectively. However, we observed extreme oxygen isotopic disequilibrium between the incrustations and lake water. Kinetic effects probably

关 键 词：碳酸盐 稳定同位素 轮藻结壳 软体动物壳体 水体环境 

分 类 号：P597[天文地球—地球化学]