Exploring the Influences of Temperature on “H-Shaped” Glycerol Dialkyl Glycerol Tetraethers in a Stratigraphic Context: Evidence From Two Peat Cores Across the Late Quaternary

Unusual “H-Shaped” branched and isoprenoidal glycerol monoalkyl glycerol tetraethers (GMGTs, or H-GDGTs) have been found in peat, lake, and ocean sediments. A survey of recent samples from a modern global peat database suggested that there is a relationship between the abundance of H-GDGTs relative to regular GDGTs and temperature. However, this relationship has not been widely explored, including in a historical, stratigraphic or geological context. Here, we report the abundance and distribution of H-iso- and H-brGDGTs in two (Hani and Gushantun) peat cores from northeastern China through the late Quaternary (last 15 kyr) to examine whether the relationship between temperature and the relative abundance of H-GDGTs is preserved downcore. The results indicate that high relative abundances of H-brGDGTs are associated with high (or increasing) reconstructed mean annual air temperature (MAAT peat ), albeit with considerable divergence in some intervals. On the other hand, high relative abundances of H-isoGDGTs are generally associated with low (or decreasing) MAAT peat . These findings are partly inconsistent with the observations from the modern database of globally distributed peats, which showed that the abundance of both (br- and iso-) H-GDGTs is positively correlated with temperature. The deviation in the relationship between H-isoGDGTs and temperature suggests that additional factors, for example pH and shifts in archaeal community related to hydrology, exert an influence on the abundance of H-isoGDGTs on the long-term.