湖泊水体微生物四醚膜脂化合物研究进展

来源于微生物膜脂的甘油二烷基甘油四醚类(GDGTs)化合物是近年来被广泛用于古环境定量重建研究的化合物之一,究其原因在于此类化合物对环境响应敏感,特别是温度与pH值等,据此而建立的一系列GDGTs指标有效定量重建海洋、湖泊、泥炭以及土壤等不同沉积载体的环境信息.目前已在全球范围广泛开展湖泊沉积物GDGTs的研究工作,相继建立的全球以及不同区域尺度的湖泊沉积物GDGTs校正方程,已被用于湖泊古环境的定量重建研究,有效记载古湖泊环境变迁信息.相较之下,基于湖泊水体GDGTs的调查工作则起步较晚,但越来越多的研究显示,不同类型湖泊水体普遍贡献GDGTs,然而究竟此类水生来源GDGTs是否与陆源以及湖泊沉积物GDGTs具有类似的分布,以及他们对环境因素的响应如何,这都为湖泊古温度定量重建研究带来不确定性.基于此,本文总结这10年来湖泊水体GDGTs研究工作的进展,首先阐述湖泊水体不同来源(古菌以及细菌)GDGTs的分布情况,研究发现水体不同层位GDGTs浓度以及各组分之间存在差异,并且水深在不同湖泊对GDGTs浓度以及各组分相对比例的影响存在差异.此外还总结湖泊水体中古菌来源isoGDGTs以及细菌来源brGDGTs的生物来源,并进一步分析环境因素对不同深度水体GDGTs分布的影响,虽然温度依然是影响水体中GDGTs分布的首要因素之一,然而湖泊水深、温度以及水体中溶解氧浓度等因素存在着一定的耦合关系,这些因素往往协同作用于水体GDGTs,因此会为评估环境因素对水体GDGTs的影响带来难度.

Occurrence and distribution of glycerol dialkyl glycerol tetraethers in lake water column: A review

Glycerol dialkyl glycerol tetraethers (GDGT) are membrane lipids that have become a useful tool in palaeoclimatology, the GDGT-based proxies have been applied to reconstruct paleoclimatic variation in marine, lake, peat bog and soils environments due to their sensitivity to environmental parameters, such as temperature and pH. Several calibrations based on the distribution of GDGTs in lake surface sediments have been established in global and regional lakes, they have been widely utilized to reconstructed environmental variation in paleolimnology. Compare to the ubiquitous occurrence of GDGTs in lake sediments, GDGTs analysis of the lake water column is limited, however, increasing evidence has demonstrated that the contribution of GDGTs from the lake water column to lake sediments is not negligible. It is thus vital to address the relationship between the distribution pattern of aquatic origin GDGTs within the lake water column and environmental factors before we apply the GDGT-based proxies in lake environments to reconstruct paleoclimate. In this paper, we first introduced the GDGTs distribution in the lake water column, to see whether there was a correlation between GDGTs distribution and water depth in terms of the GDGT concentration and the fractional abundance of individual GDGTs. We also reviewed the biological source of the archaea derived isoGDGTs and bacteria-derived brGDGTs of the lake water column, respectively. Further, we found that temperature was still one of the main controlling environmental factors that influence the fractional abundance of GDGTs and other related GDGT-based proxies in the lake water column, however, it is worth noting that the coupling relationship between temperature, water depth and dissolved oxygen in the lake could complicate the GDGTs distribution in the water column.