Understanding Microbial Lipid (GDGTs and 3-OH FAs) Responses Across Arctic Ecological Gradients

Lipid biomarkers such as glycerol dialkyl glycerol tetraethers (GDGTs) and 3-hydroxy fatty acids (3-OH FAs) are widely used proxies for paleoenvironmental reconstruction. To evaluate their applicability in high-latitude environments, we analyzed samples from seven soil trenches collected at 5 cm intervals to a depth of ~40 cm, fifteen surface soils, and nine fjord sediments from the Ny-Ålesund region of Svalbard. The datasets were compared to assess the relative performance of lipid-based proxies under Arctic conditions. Soils from Svalbard display higher proportion of 6-methyl branched GDGTs compared to most global soils. Although the overall concentrations of branched and isoprenoid GDGTs are relatively low, likely due to the cold climate and short growing season. The microbial lipid derived pH proxy, performs reliably in extreme setting. In contrast, the temperature index, MBT′_5ME values show substantial variability despite limited temperature variation, suggesting that temperature is not the sole factor affecting the lipid distribution. Depth-profile analyses of brGDGTs in moss-dominated soils reveal that moss-covered areas contribute significantly to brGDGT abundance. Moss-derived organic matter enhances bacterial activity and lowers the fungal-to-bacterial ratio within the microbial community. This interpretation is supported by stable carbon isotope (δ¹³C) and total organic carbon (TOC) data, which suggest that mosses are the primary source of organic carbon supporting brGDGT production. Overall, finding highlight the important role of moss cover in regulating microbial processes and GDGT distributions in Arctic soils, emphasizing the need to consider vegetation effects when applying lipid-based proxies in high-latitude paleoclimate reconstructions.