样品保存过程中降解对GDGTs环境代用指标的影响

微生物细胞膜脂甘油二烷基甘油四醚（GDGTs）样品在实验室冰箱储存过程中可能会遭受降解，进而对GDGTs各指标应用的准确性产生影响.了解GDGTs各类化合物抗降解能力的差异能够为指标的准确应用提供重要的判别手段.2017年，通过对2012年的石笋样品提取物（GDGTs）进行二次测试，发现GDGTs化合物绝对含量明显减少且各化合物的相对含量变化明显:细菌brGDGTs含量相对于古菌isoGDGTs含量变化较小，对应的干旱化指标R_i/b值略有减小，陆源输入指数BIT值增大，故细菌brGDGTs化合物在保存过程中更稳定；古菌isoGDGTs含环少的化合物变化较小，环化指数CBT值增加，表明少环的化合物在降解过程中更稳定；基于古菌isoGDGTs建立的古温度指标TEX₈₆值显著降低；基于细菌brGDGTs建立的甲基化指数MBT值增加，表明甲基越多的化合物越易降解. 

The Impact of Degradation on the Tetraether-Based Proxies during the Sample Storage

The glycerol dialkyl glycerol ether (GDGTs) may be subjected to degradation during the sample storage, which may have an effect on the application of GDGTs. Thus, it is important to understand the resistance of GDGTs compounds to degradation for the accurate application of GDGT derived proxies. In this study, the extractions (GDGTs) of stalagmite sample from the year of 2012 was reanalyzed in 2017. It is found that the absolute concentration of GDGTs has decreased and the relative content of each component has changed significantly. The change of the concentration of bacterial brGDGT is smaller than that of the archaeal isoGDGTs, which corresponds to the decreased R_i/b value and increased BIT values. Therefore, compared to the isoGDGTs, the brGDGTs are more stable during the processes of degradation. Smaller changes of the concentration of archaeal isoGDGTs of less-cyclic-moieties and increasing CBT values indicate that GDGTs with fewer rings tend to be more stable during the degradation processes. The isoGDGTs based TEX₈₆ values also decrease significantly. The increasing of the brGDGTs based MBT values show that GDGTs with more cyclopentyl moieties are more easily to be degraded.