Global distribution patterns of hydroxy glycerol dialkyl glycerol tetraethers

Archaea are ubiquitous in mesophilic and extremophilic environments. Variations in lipid composition of their unique tetraether membrane allow them to maintain integrity and permeability in moderate to extreme environmental conditions. The change in the number of cyclic moieties in their membrane lipids is argued to be an adaptation to ambient temperatures, which is used to estimate past water surface temperature via the TEX86 index. A new class of GDGTs with a hydroxylation in one of the alkyl chains has recently been described in marine sediments. Here we report that these hydroxy-GDGTs are widespread and abundant in mesophilic marine and lacustrine environments. Moreover we observe increasing hydroxy-GDGT contributions towards higher latitudes and lower water temperatures. A significant correlation between the relative abundance of hydroxy-GDGTs and temperature is observed in surface sediments. As these compounds are found both in modern and downcore samples we suggest that the hydroxy-GDGTs could be included in the GDGT paleoproxy tool kit.