Distribution of glycerol dialkyl glycerol tetraethers in surface soils along an altitudinal transect at cold and humid Mountain Changbai: Implications for the reconstruction of paleoaltimetry and paleoclimate

Glycerol Dialkyl Glycerol Tetraethers(GDGTs)serve as important tools for the quantitative reconstruction of paleoclimate and paleoecology in both continental and marine environments.Previous studies of GDGTs in the terrestrial environments focused primarily on the soils from the relatively warm-humid or cold-dry regions.However,it is still unclear how GDGTs respond to environmental variables in the cold-humid regions.Here,we collected soils along an altitudinal transect of Mountain(Mt.)Changbai,which has a typical cold-humid climate,to investigate the distribution of GDGTs and the response of GDGT-based proxies to changes in climate along the transect.The shift in the distribution of archaeal isoprenoidal GDGTs(iso GDGTs)revealed that the archaeal community varied significantly along the transect,which can affect the relationship between TEX86and mean annual air temperature(MAT).In addition,the increased temperature seasonality at higher altitudes exerted a significant impact on TEX86.We proposed a global calibration of TEX86for the growing season temperature reconstruction in the soil environments:T=85.19×TEX86-46.30(R2=0.84,p<0.001).The methylation indices for 5-methyl branched GDGTs(br GDGTs)including MBT′5meand MBT5/6,showed correlation with soil water content but no relationship with MAT,indicating that MBT′5meand MBT5/6from cold-humid environments may be not suitable for temperature and altitude reconstruction.In contrast,the recently developed p H proxies,including MBT′6me(the methylation index for 6-methyl br GDGTs),CBT(Cyclisation index of Branched Tetraethers),IRIIa’(Isomer ratio of IIa′)and IRIIIa′(Isomer ratio of IIIa′)exhibited significant correlations with soil p H,suggesting these proxies can still be used for soil p H reconstruction in the coldhumid regions.The combination of MBT′5meand MBT′6mewas strongly related to different types of climate(cold-dry,warmhumid,cold-humid,and warm-dry).For example,MBT′5me<0.65 and MBT′6me>0.55 are diagnostic for the cold-humid climate.Thus,the combination of MBT′5meand MBT′6mehas the potential as a tool for the identification of different types of paleoclimate.