Evaluation of glycerol dialkyl glycerol tetraether proxies for reconstruction of the paleo-environment on the Qinghai-Tibetan Plateau

The uplift of the Qinghai-Tibetan Plateau has a great effect on local and global climate changes. Here we report the late Holocene climate change in the northern plateau by using a 3490-year sediment core record from Kusai Lake. Glycerol dialkyl glycerol tetraethers (GDGTs) collected from the core were examined in combination with other paleo-environmental proxies. The reconstructed mean annual air temperatures (MAAT) using branched GDGT (membrane lipids of certain bacteria) proxies are higher than the measured MAAT, but much closer to measured summer air temperatures, suggesting a possibility of a bias of the reconstructed MAAT towards summer temperatures. The pH values derived from a branched GDGT proxy show a negative correlation with TOC (a lake productivity indicator in arid regions). Furthermore, both CBT-pH and TOC show temporal cyclic changes, which suggest that the branched GDGT derived pH index may be useful in reconstructing paleo-pH values in a lacustrine system. Lastly, the composition of isoprenoid GDGTs (membrane lipids of archaea) shows a major shift around 1400 BP, which is in line with a large increase in sediment soluble salts at this time, but lags behind the onset of salt mineral precipitation by 600 yr, suggesting that change in archaeal community composition and salt mineral precipitation may require different threshold values of salinity. The results of this study demonstrate that useful paleo-climatic and paleo-environmental information can be extracted from the GDGTs preserved in lake sediments.