中亚阿尔泰山南坡表土和泥炭沉积物GDGTs综合研究

INTEGRATED INVESTIGATION OF GDGTs IN SURFACE SOILS AND PEAT SEDIMENTS IN THE SOUTHERN ALTAI MOUNTAINS IN ARID CENTRAL ASIA

相对于我国季风区,西北内陆地区表土和泥炭沉积物的甘油二烷基甘油四醚化合物(GDGTs)现代过程研究结果报道较少。对中亚干旱区阿尔泰山南坡海拔梯度表土、高山泥炭地哈拉沙子和那仁夏周边坡地表土以及哈拉沙子表层泥炭沉积物进行了GDGTs分析,结果表明:1)其海拔梯度表土当中细菌来源支链结构GDGTs(brGDGTs)的分子分布特征主要响应于湿度的变化;2)同样主要由于湿度变化的影响,奇古菌的影响和贡献在相对低海拔地区更为明显,产甲烷古菌的影响和贡献在相对高海拔地区上升,导致古菌来源的类异戊二烯结构GDGTs(isoGDGTs)的TEX86参数随海拔上升具有显著的降低趋势;3)哈拉沙子和那仁夏泥炭地泥炭沉积物当中的brGDGTs和isoGDGTs都并非主要来自周边坡地土壤的异源输入,而主要都是泥炭地原地自生来源。这些研究结果,一方面为在该区域利用GDGTs开展古环境、古气候重建提供基础性参考;另一方面,也对其他区域相应研究结果形成有益补充。

Glycerol Dialkyl Glycerol Tetraethers(GDGTs)are considered to paly an important role in reconstructing paleoclimate in both continental and marine environments.Previous studies of GDGTs in the terrestrial environments focus primarily on the surface soil from the monsoonal humid China.However,the equivalent studies in arid inland China are rarely reported,especially on the sources of GDGTs in peat sediments.In order to further understand the main climate control factors of the molecular distribution characteristics of GDGTs in surface soils,as well as the major source(s)of GDGTs in peat sediments,we investigated the distribution of GDGTs of surface soils and surface peat sediments in the southern Altai Mountains in arid Central China(47°56'~48°48'N,86°55'~88°23'E).This region belongs to the typical temperate continental climate,with long cold winters and short summers.We collected 42 samples,including 13 surface soils along an altitudinal transect(ca.1100~2500 m a.s.l.),11 surface soils from surrounding slopes of the alpine Sahara sand peatland(SSP;48°06'N,88°21'E;2446 m a.s.l.),4 surface soils from surrounding slopes of the Narenxia peatland(NRX;48°48'N,86°55'E;1763 m a.s.l.)and 14 surface peat sediments in the SSP.GDGTs in above samples were analyed by using the high performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry(HPLC-APCI-MS).The results show that:(1)The molecular distributions of the branched GDGTs(brGDGTs)in altitudinal surface soils in southern Altai Mountains are primarily responded to the changes of humidity,resulting in no significant correlation between MBT'5ME and altitude.This implies it should be cautious to use the soil brGDGTs for paleotemperature reconstructions in cold regions.(2)TEX86 of the isoprenoid GDGTs(isoGDGTs)in altitudinal surface soils have a significant decreasing trend with the increasing altitudes.It is also mainly in response to changes in humidity,demonstrating that the influence and contribution of Thaumarchaeota and Methanogens to isoGDGTs are relatively more obvious in relatively lower and higher altitudes,respectively.(3)Both the brGDGTs and isoGDGTs in the peat sediments of SSP and NRX are not mainly sourced from the surface soils in the uplands,but are mainly sourced from in situ origins.This means that the GDGTs results from regional surface soils are not suitable modern references for the paleoclimatic interpretations of the peat GDGTsrelated records from the Altai Mountains.That is,the regional peat-specific modern GDGTs investigations are needed for the reliable paleoclimatic interpretations of the peat GDGTs-related records from the Altai Mountains.In general,all the results provide fundamental references for the applications of GDGTs in paleoclimatic studies in arid Central Asia.From another aspect,all the results are beneficial complements to the study results of GDGTs from other regions.