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Abstract:
Bacterial and archaeal lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs) and dialkyl glycerol
diethers, are increasingly used as proxies for specific environmental parameters, such as air temperature
and soil pH in lacustrine environments. Little is known, however, about the distribution and applicability
of bacterial and archaeal lipids on the Tibetan Plateau. We investigated nine different watersheds across
the plateau by way of sediments from lakes and rivers, as well as the surrounding soils. Our transect
study included a salinity gradient and focused on saline lakes, which are rarely examined. We analyzed
archaeal isoprenoid (i) and bacterial branched (b) GDGTs, as well as archaeol to trace their sources and
environmental factors, influencing their distributions. We could show that iGDGTs were produced
in situ and bGDGTs were primarily soil-derived although we could not exclude in situ production of
bGDGTs in the lakes. The most important environmental variables correlating with GDGT distributions
were temperature and salinity. Bacterial GDGT distributions correlated mainly with salinity, while archaeal
lipid distributions correlated with temperature. Based on the correlation of methylation (MBT0) and
cyclisation (CBT) indices of bGDGTs with pH and mean annual air temperature (MAAT), we established
local calibrations for the Tibetan lakes. TEX86 could also be applied to reconstruct temperature, which
was strongly biased towards measured summer lake water temperature, indicating enhanced production
of iGDGTs in the summer months. Existing proxies show, therefore, potential for palaeoclimate reconstruction on the Tibetan Plateau if local calibrations are applied.
