Calibration of the U 37 K′ index of long-chain alkenones with the in-situ water temperature in Lake Qinghai in the Tibetan Plateau

Abstract

Long-chain alkenones (LCAs) can potentially be used as indicators to understand past variations in lacustrine environments. Previous research has suggested that the relationship between the temperature and the unsaturation index of LCAs should be calibrated individually, because of the possible variations in the alkenone-producing algal species in the lacustrine environment. In this work, we have calibrated U 3 K 7 ′ of water filter samples against the in-situ water temperature in Lake Qinghai, Tibetan Plateau. There are significant relationships between U 3 7 ′ and the water temperature, a non-linear relationship was derived. Because the U 3 7 ′ values did not respond sensitively at lower temperatures, we suggested that a quadratic regression (U3 K 7 ′ =0.0011×T 2 –0.0201× T+0.1959, n=15, r 2 =0.74) was appropriate than linear regression to represent the relationship between the in-situ temperatures and U 3 K 7 ′ . Meanwhile, the U 3 K 7 correlation relationship was not more significant than U 3 7 ′ index in our study. Because of the C37:4 effects by salinity change, we suggest U3 7 is not as robust as the U3 7 ′ index as a temperature proxy, at least for the salt lake in the Tibetan Plateau. The calibration of the U 3 7 ′ index in this work has provided a new understanding of historic climatic changes in the Tibetan Plateau.