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 (isoGDGTs) revealed that the archaeal community varied significantly along the transect, which can affect the relationship between TEX 86 and mean annual air temperature (MAT). In addition, the increased temperature seasonality at higher altitudes exerted a significant impact on TEX 86 . We proposed a global calibration of TEX 86 for the growing season temperature reconstruction in the soil environments: T =85.19×TEX86−46.30 ( R 2 =0.84, p <0.001). The methylation indices for 5-methyl branched GDGTs (brGDGTs) including MBT′ 5me and MBT 5/6 , showed correlation with soil water content but no relationship with MAT, indicating that MBT′ 5me and MBT 5/6 from cold-humid environments may be not suitable for temperature and altitude reconstruction. In contrast, the recently developed pH proxies, including MBT′ 6me (the methylation index for 6-methyl brGDGTs), CBT (Cyclisation index of Branched Tetraethers), IR IIa ’ (Isomer ratio of IIa′) and IR IIIa ′ (Isomer ratio of IIIa′) exhibited significant correlations with soil pH, suggesting these proxies can still be used for soil pH reconstruction in the coldhumid regions. The combination of MBT′ 5me and MBT′ 6me was 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′ 5me and MBT′ 6me has the potential as a tool for the identification of different types of paleoclimate.