湖泊摇蚊亚化石氧同位素:一种有效的古气候代用指标

OXYGEN ISOTOPE OF THE LACUSTRINE CHIRONOMID SUBFOSSILS:AN USEFUL PROXY FOR THE PALEOCLIMATIC RECONSTRUCTION

湖泊沉积物摇蚊亚化石的氧同位素作为一种新的指标,近来成为古气候重建的一种重要手段。本文在综述摇蚊亚化石氧同位素的来源特征、迁移过程及影响因素的基础上,揭示了其在古气候重建研究中的原理、优势、应用范围,并介绍了目前存在的实验技术瓶颈(生物体内氧同位素的提取)及其进展。本文着重涉及以下内容:(1)湖泊沉积物中摇蚊亚化石相较其它微体生物指标有易保存、个体大显著优势,方便提取足量的样品进行氧同位素分析;(2)摇蚊头壳氧同位素含量的影响因素众多,室内控制实验成果表明其幼虫体内约69%的氧都来自于栖息地的水中,而与食物中的氧同位素关系不显著,因此为摇蚊头壳中氧同位素信号的解释、历史气候条件的重建提供了重要的理论依据;(3)实验分析技术定量评估了不同实验方案(如化学处理、样品量大小、锡箔容器等)的误差;同时同位素质谱仪技术的发展极大的方便了测量过程。(4)摇蚊头壳氧同位素能较好地重建历史气温及降水的情况,但目前主要研究工作在欧美高山、极地地区展开。

As an new proxy, the oxygen isotope analysis based on chironomid subfossils in lake sediments has become an important tool to reconstruct paleoclimate. On the basis of summarizing the source, migration process and influen cing factors of the stable oxygen isotope in chironomid subfossils, this paper reveals its principle and application in pa- leoclimatic research and the existing experimental bottleneck. The main progresses include： （1） Chironomid subfos- sils are well preserved and of relatively large size in individual, which facilitate extracting enough samples for oxygen isotope analysis and has significant advantages over other microbiological indicators in lake sediments; （2） There are many factors affecting the oxygen isotope of chironomid. Previous research indicates about 69% of the oxygen in the larvae was from the habitat, which shows no significant relationship with the oxygen isotope in its food. Therefore, it provides important theoretical basis for interpreting the stable oxygen signal in chironomid head capsules and recon- structing the historical climate conditions; （3） The experimental technology has been greatly improved and relevant error of different experimental designs （such as chemical treatment, sample size and tin foil container, etc. ） has been evaluated quantitatively. At the same time, the development of isotope mass spectrometry technology has greatly fa- cilitated the measurement process. （4） Oxygen isotope signals in ehironomid subfossils provide a reliable means in pa- leoelimate reconstructions, particularly for temperature and precipitation, although most of those studies were based on alpine/arctic area in Europe and North America.