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Variations in geochemical characteristics of sedimentary deposits, also known as
geochemical climate proxies, are important tools for elucidating paleoclimatological variability.
Lipids of biological origin, which are preserved in sediments due to their recalcitrant nature,
form an important class of organic geochemical climate proxies and are being increasingly used
for paleoclimatological reconstructions. However, the lipid-based climate proxies can themselves
be influenced by various environmental and biological conditions, which may limit their
applicability. Investigation of such environmental and biological influences on various lipidbased
climate proxies is therefore important in order to avoid spurious paleoclimatological
reconstructions.
This study involves the investigation of various environmental and biological factors that
can influence two climate proxies based on lipids, namely, (1) hydrogen isotopic composition of
lipids, which is primarily used to infer variations in hydrological conditions in the geological
past, and (2) paleotemperature proxies based on the distribution of lipids known as glycerol
dialkyl glycerol tetraether (GDGT) in soils.
Results obtained from this study indicate that hydrogen isotope ratios of lipids are
influenced by the growth conditions of lipid-synthesizing organisms, in addition to the hydrogen
isotope ratios of ambient water. Significant variations in lipid hydrogen isotope ratios were
observed due to variations in carbon substrate, growth temperature and salinity of growth media.
Furthermore, the results also demonstrate that precipitation amount is a strong controlling factor
of the paleotemperature proxies based on soil GDGT lipids, in addition to mean annual
temperature. These findings will be crucial for proper application of these climate proxies for
obtaining better paleoclimatological reconstructions. |